S-3 1 tm2523066d1_s3.htm FORM S-3

As filed with the Securities and Exchange Commission on August 13, 2025

Registration No. 333-

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Armata Pharmaceuticals, Inc.

(Exact name of registrant as specified in its charter)

Washington	91-1549568
(State or other jurisdiction	(I.R.S. Employer
of incorporation or organization)	Identification Number)

5005 McConnell Avenue

Los Angeles, California 90066

(310) 665-2928

(Address, including zip code, and telephone number,
including area code, of registrant’s principal executive offices)

Deborah L. Birx, M.D.

Chief Executive Officer

Armata Pharmaceuticals, Inc.

5005 McConnell Avenue

Los Angeles, California 90066

(310) 665-2928

(Name, address, including zip code, and telephone number,

including area code, of agent for service)

Copies to:

Jared N. Fertman

Andrew C. Marmer

Willkie Farr & Gallagher LLP

787 Seventh Avenue

New York, New York 10019

(212) 728-8000

(Approximate date of commencement of proposed sale to the public) From time to time after the effective date of this Registration Statement, as determined by the registrant.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box: ¨

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box: x

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ¨

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer	¨	Accelerated filer	¨
Non-accelerated filer	x	Smaller reporting company	x
		Emerging growth company	¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of Securities Act. ¨

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment that specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the U.S. Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where such offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED AUGUST 13, 2025

PROSPECTUS

$100,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

Units

From time to time, we may sell up to an aggregate of $100,000,000 of our common stock, preferred stock, debt securities, warrants or units in any combination of the foregoing, in amounts, at prices and on terms described in one or more supplements to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings.

Our common stock is traded on the New York Stock Exchange (the “NYSE”) American under the trading symbol “ARMP.” On August 11, 2025, the last reported sale price of our common stock on the NYSE American was $2.36.

The preferred stock, debt securities, warrants and units described in this prospectus have not been approved for listing on any market or exchange, and we have not made any application for such listing.

This prospectus describes the general terms of the securities we may offer and the general manner in which we may offer these securities. Each time we sell securities described herein, we will provide prospective investors with a supplement to this prospectus that will contain specific information about the terms of that offering, including the specific amounts, prices and terms of the securities offered. Such prospectus supplements may also add, update or change information contained in this prospectus. The applicable prospectus supplement will contain information, where applicable, as to any other listing on the NYSE American or any other securities market or other exchange with respect to the securities covered by such prospectus supplement.

Our principal executive offices are located at 5005 McConnell Avenue, Los Angeles, California 90066, and our telephone number at that address is (310) 665-2928.

You should read this prospectus and any prospectus supplement carefully before you invest.

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INVESTING IN OUR SECURITIES INVOLVES A HIGH DEGREE OF RISK. YOU SHOULD REVIEW CAREFULLY THE RISKS AND UNCERTAINTIES REFERENCED UNDER THE HEADING “RISK FACTORS” ON PAGE 8 OF THIS PROSPECTUS AND “ITEM 1A—RISK FACTORS” OF OUR MOST RECENT ANNUAL REPORT ON FORM 10-K OR QUARTERLY REPORT ON FORM 10-Q THAT IS INCORPORATED BY REFERENCE IN THIS PROSPECTUS, AS WELL AS THOSE CONTAINED IN THE APPLICABLE PROSPECTUS SUPPLEMENT AND ANY RELATED FREE WRITING PROSPECTUS, AND UNDER SIMILAR HEADINGS IN THE OTHER DOCUMENTS THAT ARE INCORPORATED BY REFERENCE INTO THIS PROSPECTUS.

This prospectus may not be used to offer or sell any securities unless accompanied by a prospectus supplement.

As of August 13, 2025, the aggregate market value of our outstanding common stock held by non-affiliates, or public float, was approximately $26.1 million, based on 11,077,705 shares of outstanding common stock held by non-affiliates as of the date of this prospectus, at a price of $2.36 per share, which was the last reported sale price of our common stock on the NYSE American on August 11, 2025. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell securities registered on the registration statement of which this prospectus is a part in a public primary offering with a value exceeding more than one-third of our public float in any 12-month period so long as our public float remains below $75.0 million. As of the date hereof, we have not offered any securities pursuant to General Instruction I.B.6 of Form S-3 during the 12 calendar months prior to and including the date of this prospectus.

The securities may be sold directly by us to investors, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. For additional information on the methods of sale, you should refer to the section entitled “Plan of Distribution” in this prospectus and in the applicable prospectus supplement. If any agents or underwriters are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such agents or underwriters and any applicable fees, commissions, discounts and options to purchase additional securities will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds that we expect to receive from such sale will also be set forth in a prospectus supplement.

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this Prospectus is , 2025.

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TABLE OF CONTENTS

ABOUT THIS PROSPECTUS	1
SUMMARY	2
RISK FACTORS	8
THE SECURITIES WE MAY OFFER	9
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	11
USE OF PROCEEDS	14
DESCRIPTION OF CAPITAL STOCK	15
DESCRIPTION OF THE DEBT SECURITIES	18
DESCRIPTION OF WARRANTS	20
DESCRIPTION OF UNITS	22
LEGAL OWNERSHIP OF SECURITIES	23
PLAN OF DISTRIBUTION	26
LEGAL MATTERS	28
EXPERTS	29
WHERE YOU CAN FIND MORE INFORMATION	30
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	31

We have not authorized anyone to provide you with information different from the information contained in or incorporated by reference in this prospectus, any applicable prospectus supplement and any related free writing prospectus that we may authorize to be provided to you. No dealer, salesperson or other person is authorized to give any information or to represent anything not contained or incorporated by reference in this prospectus, any applicable prospectus supplement or any related free writing prospectus that we may authorize to be provided to you. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. You should assume that the information in this prospectus, any applicable prospectus supplement or any related free writing prospectus is accurate only as of the date on the front of the document and that any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus, any applicable prospectus supplement or any related free writing prospectus, or any sale of our securities. Our business, financial condition, results of operations and prospects may have changed since that date.

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the U.S. Securities and Exchange Commission, or the SEC, using a “shelf” registration process. Under this shelf registration process, we may offer and sell, either individually or in combination, in one or more offerings, any combination of the securities described in this prospectus, for total gross proceeds of up to $100,000,000.

This prospectus provides you with a general description of the securities we may offer. Each time we offer securities under this prospectus, we will provide a prospectus supplement that will contain more specific information about the terms of those securities and the offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. We may also add, update or change in the prospectus supplement (and in any related free writing prospectus that we may authorize to be provided to you) any of the information contained in this prospectus or in the documents that we have incorporated by reference into this prospectus. We urge you to carefully read this prospectus, any applicable prospectus supplement and any related free writing prospectus, together with the information incorporated herein by reference as described under the headings “Where You Can Find More Information” and “Incorporation of Certain Information by Reference” before buying any of the securities being offered.

SUMMARY

The following summary highlights information contained elsewhere in this prospectus or incorporated by reference herein and does not contain all the information that may be important to purchasers of our securities. You should carefully read this prospectus, all documents incorporated by reference, any prospectus supplement and any related free writing prospectus, and the additional information described under the caption “Where You Can Find More Information” in this prospectus, before buying any of the securities being offered. References in this prospectus to “Armata,” the “Company,” “we,” “us” and “our” refer to Armata Pharmaceuticals, Inc. and its subsidiaries, on a consolidated basis, unless the context requires otherwise.

Our Company

We are a clinical-stage biotechnology company focused on the development of high-purity, pathogen-specific bacteriophage therapeutics for the treatment of antibiotic-resistant and difficult-to-treat bacterial infections using our proprietary bacteriophage-based technology. We have completed three Phase 2 clinical trials to date. We see bacteriophages as a potentially safer and effective alternative to antibiotics and an essential response to the growing bacterial resistance to current classes of antibiotics. Bacteriophages or “phages” have a powerful and highly differentiated mechanism of action that enables binding to and killing of specific targeted bacteria while uniquely preserving the normal human microbiome or “healthy bacteria”. This is in direct contrast to traditional broad-spectrum antibiotics which can alter the human microbiome increasing susceptibility to opportunistic pathogens, such as Clostridium difficile. We believe that phages represent a promising means to effectively treat bacterial infections as an alternative to broad-spectrum antibiotics, especially for patients with bacterial infections resistant to current standard of care therapies, including the multidrug-resistant or “superbug” strains of bacteria. We are a leading developer of clinical-stage phage therapeutics of high purity, and believe we are uniquely positioned to address the growing worldwide threat of antibiotic-resistant bacterial infections.

We are combining our proprietary approach and expertise in identifying, characterizing and developing both naturally occurring and engineered (synthetic) bacteriophages with our proprietary phage-specific host-engineered current Good Manufacturing Practices (“cGMP”) manufacturing capabilities to advance a target pipeline of high-quality bacteriophage product candidates for late-stage clinical development. Our optimized manufacturing processes significantly increase phage titers and improve production efficiency with the goal of ensuring commercial viability.

We remain committed to our mission to evaluate phage-based therapeutics in randomized controlled clinical trials that evaluate safety and efficacy required to support potential regulatory approval and commercialization of our phage products as alternatives to traditional antibiotics, providing a potential method of treating patients suffering from drug-resistant and difficult-to-treat bacterial infections. To date, we have completed three critical Phase 2 trials, utilizing two distinct phage cocktails against two different bacterial pathogens with the potential to treat chronic pulmonary disease complicated by bacterial infection, as well as acute systemic bacterial infection. We believe that we are uniquely advancing our two lead candidates, referred to as AP-PA02 and AP-SA02, to address both chronic and acute bacterial infections.

Pseudomonas aeruginosa Phage Product Candidate, AP-PA02

Clinical Development of AP-PA02 in Cystic Fibrosis: Completed Phase 1b/2a Study

Our first phage candidate, inhaled AP-PA02, is focused primarily on the treatment of chronic pulmonary infections due to Pseudomonas aeruginosa (“P. aeruginosa”). On October 14, 2020, we received the approval to proceed from the U.S. Food and Drug Administration (the “FDA”) for our Investigational New Drug (“IND”) application for AP-PA02. In the first quarter of 2023, we announced positive topline results from the completed “SWARM-P.a.” study – a Phase 1b/2a, multicenter, double-blind, randomized, placebo-controlled, single ascending dose and multiple ascending dose clinical trial to evaluate the safety and tolerability of inhaled AP-PA02 in subjects with cystic fibrosis and chronic pulmonary P. aeruginosa infection. Data indicate that AP-PA02 was well-tolerated with a treatment emergent adverse event profile similar to placebo. Pharmacokinetics findings confirm that AP-PA02 can be effectively delivered to the lungs through nebulization with minimal systemic exposure, with single ascending doses and multiple ascending doses resulting in a proportional increase in exposure as measured in induced sputum. AP-PA02 exposures were generally consistent across subjects. Additionally, bacterial levels of P. aeruginosa in the sputum measured at several timepoints suggest improvement in bacterial load reduction for subjects treated with AP-PA02 at the end of treatment as compared to placebo after ten days of dosing. In addition, a correlation was seen between increasing phage dose (higher AP-PA02 exposures) and reduction in the bacterial load, supporting the biologic plausibility of a bacterial specific mechanism of action and creating the opportunity for phage as a therapeutic alternative to inhaled antibiotics. This study was supported by the Cystic Fibrosis Foundation (the “CFF”), which granted us a Therapeutics Development Award of $5.0 million. We received the full award’s amount, including the final payment of $0.3 million, in January 2024. Following the promising Phase 1b/2a results of favorable safety and tolerability profile and plausible mechanism of action, an additional confirmatory Phase 2 trial was initiated in non-cystic fibrosis bronchiectasis (“NCFB”) patients with similar chronic pulmonary disease with infections due to P. aeruginosa.

Clinical Development of AP-PA02 in Non-Cystic Fibrosis Bronchiectasis: Completed Phase 2 Study

On February 22, 2022, Armata announced that it had received from the FDA the approval to proceed for our IND application for AP-PA02, in a second indication, NCFB. On December 19, 2024, Armata announced encouraging results from the completed “Tailwind” study – a Phase 2 multicenter, double-blind, randomized, placebo-controlled study to evaluate the safety, phage kinetics, and efficacy of inhaled AP-PA02 in subjects with NCFB and chronic pulmonary P. aeruginosa infection. Data indicated that inhaled AP-PA02 provides a durable reduction of P. aeruginosa in the lung, with a favorable safety and tolerability profile. The Tailwind study was conducted in two cohorts running in parallel: subjects in one cohort (cohort A) received inhaled AP-PA02 as monotherapy, while subjects in another cohort (cohort B) received inhaled AP-PA02 in combination with inhaled anti-pseudomonal antibiotic treatment. Subjects in both cohorts were dosed at home by nebulization with study drug administered every 12 hours for 10 days and were followed for approximately four weeks after receiving their last dose of study drug. The primary efficacy endpoint was the reduction in P. aeruginosa colony forming units (“CFUs”) in lung sputum at one week following completion of dosing (day 17) compared to baseline. Per the statistical analysis plan, efficacy analysis of each independent cohort showed no significant difference between subjects treated with AP-PA02 and placebo due to small numbers of subjects in each cohort. Notably, a post-hoc intent-to-treat analysis (n=33 active and n=15 placebo; all subjects from both cohorts) demonstrated a statistically significant reduction of P. aeruginosa CFUs in the lung at day 17 (AP-PA02 vs. placebo; P=0.05). The reduction in P. aeruginosa CFUs persisted two weeks following completion of dosing with AP-PA02 when compared with placebo at day 24 (AP-PA02 vs. placebo; P=0.015). Additionally, paired analysis of P. aeruginosa CFU density at baseline compared to day 10 (P=0.03), day 11 (P=0.01), day 17 (P=0.003) and day 24 (P=0.018) was significant in the AP-PA02-treated cohort. We believe the data suggest that AP-PA02 alone is as effective as the combination therapy of phage and antibiotics in reducing P. aeruginosa CFUs in the lung. Additionally, approximately one-third of subjects treated with phage monotherapy exhibited at least a 2-log CFU reduction in P. aeruginosa compared to no reduction in placebo treated subjects. Safety data indicate that inhaled AP-PA02 was well-tolerated with treatment-emergent adverse events mild and self-limiting. There was one possibly related serious adverse event that was linked to an acute pulmonary event requiring hospitalization that was responsive to antibiotics. We believe the safety and tolerability of AP-PA02 offers a promising profile for treating chronically infected NCFB patients.

Results from the Phase 2 Tailwind study demonstrate the potential of Armata’s high-purity phage cocktail, AP-PA02, as a new monotherapy treatment alternative for chronic pulmonary disease caused by P. aeruginosa infection, including drug-resistant bacteria, and indicate the potential for phage therapy to reduce reliance on chronic antibiotic use. The Phase 2 Tailwind study represents the second successful clinical trial for AP-PA02, Armata’s lead pulmonary candidate, which was first evaluated in people with cystic fibrosis in the Phase 1b/2a SWARM-P.a. trial that completed in 2023. We believe the learnings on dose-schedule regimens gained from the two completed Phase 2 studies position us to define a safe and promising biologic correlation for a Phase 3 definitive trial to evaluate inhaled AP-PA02 as an alternative to antibiotics in chronic pulmonary P. aeruginosa infection.

Contingent upon securing sufficient additional funding, we may at the appropriate time in the future resume clinical development of AP-PA02 for NCFB, which may include the execution of a definitive Phase 3 clinical trial. We are also actively exploring potential strategic partnerships as a means to further advance this important program.

Additional Clinical Indications for AP-PA02

The current Pseudomonas phage cocktail formulated for inhalation (AP-PA02) is prepared with the same high potency and purity of our injectable phage cocktail for Staphylococcus aureus (“S. aureus”) (AP-SA02). Based on the AP-SA02 clinical findings, we are exploring the potential development of our Pseudomonas phage cocktail for acute ventilator-associated pneumonia and severe infections due to multidrug-resistant P. aeruginosa.

Staphylococcus aureus Phage Product Candidate, AP-SA02

Clinical Development of AP-SA02 in Bacteremia: Completed Phase 1b/2a Study

In parallel to developing novel phage therapeutics that target chronic bacterial infections, we have an acute bacterial infection clinical development plan focused on S. aureus bacteremia, a difficult-to-treat and often life-threatening human infection that can result in high morbidity and mortality and for which bacterial resistance to antibiotics is growing.

A key advantage of our phage manufacturing expertise is the purity profiles of our phage products, including AP-SA02, our phage product candidate for S. aureus; this has enabled us to pursue treatment of complicated S. aureus bacteremia, where repetitive intravenous dosing is required. On June 15, 2020, we entered into an agreement (the “MTEC Agreement”) with the Medical Technology Enterprise Consortium (“MTEC”), pursuant to which we received a $15.0 million award and entered into a multi-year program administered by the U.S. Department of Defense (the “DoD”) through MTEC and managed by the Naval Medical Research Command – Naval Advanced Medical Development with funding from the Defense Health Agency and Joint Warfighter Medical Research Program. On September 29, 2022, the MTEC Agreement was modified to increase the total award by $1.3 million to $16.3 million and extend the term into the second half of 2024. On July 29, 2024, the MTEC Agreement was modified to increase the total award by $5.3 million to $21.6 million and extend the term into the third quarter of 2025. On April 29, 2025, we received $4.65 million of additional non-dilutive award funding through MTEC, thereby increasing the total MTEC award to $26.2 million, and the MTEC Agreement was modified to extend the term to September 30, 2025. On July 2, 2025, the MTEC Agreement was modified to extend the term to March 31, 2026. We are using the award to partially fund a Phase 1b/2a, multicenter, randomized, double-blind, placebo-controlled dose escalation study to assess the safety, tolerability and efficacy of our phage-based candidate, AP-SA02, for the treatment of adults with S. aureus (the “diSArm” study) and to support activities required for an end-of-Phase 2 meeting with the FDA.

On November 17, 2021, we announced that we had received approval from the FDA to proceed with our IND application for AP-SA02.

On May 19, 2025, we announced positive topline data from the Phase 1b/2a diSArm study of intravenously administered AP-SA02 in complicated S. aureus bacteremia. The diSArm study (NCT05184764) was a Phase 1b/2a, multicenter, randomized, double-blind, placebo-controlled, multiple ascending dose escalation study of the safety, tolerability, and efficacy of intravenous AP-SA02 in addition to best available antibiotic therapy (BAT) compared to BAT alone (placebo) for the treatment of adults with complicated SAB. All doses of AP-SA02 were dosed intravenously every six hours for five days. The primary clinical efficacy endpoint for the Phase 2a portion of the diSArm study was clinical outcome (responder rate) in subjects with complicated bacteremia, measured at (i) Test of Cure (TOC) for AP-SA02, defined as one week following the end of IV treatment with AP-SA02 (day 12), (ii) TOC for BAT, defined as one week following the end of IV BAT, and (iii) end of study (EOS), defined as four weeks following the end of IV BAT. Clinical outcome was evaluated by both the blinded investigators and a blinded Clinical Efficacy Adjudication Committee (CEAC) in the intent-to-treat (ITT) population.

Safety and efficacy were assessed in the ITT population, which included all subjects (n=50) who received at least one dose of AP-SA02 or placebo. AP-SA02 was well-tolerated with no serious adverse events related to the study drug. Two subjects had adverse events that were possibly related to the study drug: one with transient liver enzyme elevation and one with hypersensitivity that resolved with discontinuation of vancomycin.

A statistically significant increase in investigator-assessed responder rate was observed at TOC for AP-SA02 (day 12) in AP-SA02 treated subjects (88%) versus placebo (58%) (p = 0.047). At TOC for BAT and at EOS, 100% of the AP-SA02 treated subjects had clinically responded (p = 0.017) versus 25% of placebo subjects considered non-responsive due to either relapse or treatment failure, consistent with the non-responder rate reported in the literature for recent phase 3 trials. Of note, the clinical response with AP-SA02 occurred regardless of whether subjects were infected with methicillin-sensitive S. aureus (MSSA) or methicillin-resistant S. aureus (MRSA). All subjects infected with MRSA and treated with AP-SA02 and BAT cleared their infection by TOC for BAT with no evidence of relapse through EOS, as compared to the relapse rate of BAT alone as noted above. Supporting the investigator assessment, clinical outcome was assessed by the CEAC, who agreed that subjects who received placebo had a 22% and 25% non-responder rate at TOC with BAT and at EOS, respectively, while 100% of the subjects who received AP-SA02 clinically responded (p = 0.025: TOC BAT; p = 0.020: EOS).

Additionally, faster time to a negative blood culture and decline of key predictors of mortality and complications in SAB, including interleukin-10 and C-reactive protein, support the improved responder rates in subjects treated with AP-SA02.

We previously demonstrated the persistence of AP-SA02 in the IV space on multiple days one hour post IV push. These trial results support AP-SA02 homing to different sites of infection, presumably penetrating biofilms, and infecting and lysing the target S. aureus bacteria, independent of antibiotic resistance patterns and site of infection.

The results from our Phase 1b/2a diSArm study are an important step forward in our effort to confirm the potent antimicrobial activity of phage therapy and the completion of the study represents a significant milestone in the development of AP-SA02, moving us one step closer to introducing an effective new treatment option to patients suffering from complicated S. aureus bacteremia. This is the first clear evidence in a randomized controlled trial of the efficacy of phage against a serious systemic pathogen that is responsible for significant morbidity and mortality in the United States.

Findings from the Phase 1b/2a study, including the favorable safety and tolerability profile of AP-SA02, inform the design of a larger definitive efficacy study to demonstrate superiority of AP-SA02 in treating complicated S. aureus bacteremia, and form the basis for an end-of-Phase 2 meeting with the FDA which the Company plans to hold in the second half of 2025. We are committed to developing a superiority pivotal trial focused on phage as an alternative to broad-spectrum antibiotics and/or antibiotic sparing to decrease the utilization of broad-spectrum antibiotics and their detrimental impact on the normal human microbiome.

Additional Clinical Indications for AP-SA02

On August 1, 2022, we announced FDA approval to proceed with our IND application for AP-SA02 in a second indication, prosthetic joint infections (“PJI”) with S. aureus. We had planned to initiate a Phase 1b/2a trial; however, in light of the growing concerns of both PJI and wound infections, we are considering revising the protocol to include both indications. Driven by data from the bacteremia study, and with sufficient funding, we may in the future initiate a Phase 1b/2a trial to assess the safety and tolerability of intravenous and intra-articular AP-SA02 as an adjunct to standard of care antibiotics in adults undergoing treatment of periprosthetic joint infections and/or wound infections caused by S. aureus.

Corporate History and Reorganization

Armata was created as a result of a business combination of AmpliPhi Biosciences Corporation, a bacteriophage development stage company (“AmpliPhi”) with C3J Therapeutics, Inc. (“C3J”), where Ceres Merger Sub, Inc., a wholly-owned subsidiary of AmpliPhi, merged with and into C3J (the “Merger”). On May 9, 2019, immediately prior to the closing of the Merger, AmpliPhi changed its name to Armata Pharmaceuticals, Inc.

C3J’s predecessor, C3 Jian, Inc., was incorporated under the laws of the State of California on November 4, 2005. On February 26, 2016, as part of a reorganization transaction, C3 Jian, Inc. merged with a wholly-owned subsidiary of C3J, and as part of this process, C3 Jian, Inc. was converted to a limited liability company organized under the laws of the State of California named C3 Jian, LLC. Prior to the Merger, C3J was privately held and was financed principally through a series of equity financings.

AmpliPhi was incorporated under the laws of the State of Washington in March 1989 as a wholly-owned subsidiary of Immunex Corporation and began operations as an independent company in 1992 as Targeted Genetics Corporation. In January 2011, AmpliPhi completed the acquisition of Biocontrol Ltd, an antimicrobial biotechnology company based in the United Kingdom, with the goal of developing their phage therapy programs using funding from the sale of our legacy gene therapy assets. In November 2012, AmpliPhi completed the acquisition of Special Phage Holdings Pty Ltd, a company based in Australia, with the goal of continuing research addressing the rapidly escalating problem of antibiotic resistance through the development of a series of bacteriophage-based treatments.

Pipeline

The following chart summarizes the status of our phage product candidate development programs and partners:

Risks Associated with Our Business and this Offering

Our business and our ability to implement our business strategy are subject to numerous risks, as more fully described in the section of this prospectus entitled “Risk Factors.” You should read these risks before you invest in our securities. We may be unable, for many reasons, including those that are beyond our control, to implement our business strategy. In particular, risks associated with our business include:

There is substantial doubt about our ability to continue as a going concern, which may affect our ability to obtain future financing and may require us to curtail our operations. We will need substantial additional financing to develop our product candidates and implement our operating plans, including to support one or more pivotal trials in 2025 and beyond. If we fail to obtain additional financing, we may be delayed or unable to complete the development and commercialization of our product candidates.

We have incurred losses since our inception and anticipate that we will continue to incur significant losses for the foreseeable future, and our future profitability is uncertain.

If we fail to develop and maintain proper and effective processes and operating procedures as a non-traditional government contractor, our ability to adhere to the DoD and related entity standards could impact our ongoing and future development financing awards from the U.S. government;

We are seeking to develop antibacterial agents using bacteriophage and synthetic phage technology, a novel approach, which makes it difficult to predict the time and cost of development. No bacteriophage products have been approved in the United States or elsewhere.

Results from interim, “topline,” and preliminary data, or preclinical studies and Phase 1 or 2 clinical trials of our product candidates or from single-patient expanded access treatments may not be predictive of the results of later stage clinical trials and are subject to audit and verification procedures that could result in material changes in the final data.

We must continue to develop manufacturing processes for our product candidates and any delay in or our inability to do so would result in delays in our clinical trials.

We rely on third parties to conduct our clinical trials and to obtain materials or supplies necessary to conduct trials or to manufacture our product candidates, and their failure to perform their obligations in a timely or competent manner may delay development and commercialization of our product candidates.

We face potential risks associated with future changes in laws and policies, including the availability of government funding for grants, staffing and funding of regulatory agencies.

The use or anticipated use of artificial intelligence (“AI”) technologies, including generative AI, by us or third parties, may increase or create new operational risks.

Our business operations and current and future relationships with clinical site investigators, healthcare professionals, consultants, third-party payors, patient organizations, and customers will be subject to applicable healthcare regulatory laws, which could expose us to penalties.

If you purchase securities in an offering, you may incur dilution.

We will have broad discretion in the use of the net proceeds from an offering and may not use them effectively.

Innoviva, Inc. (“Innoviva”) our principal stockholder, beneficially owns greater than 50% of our outstanding shares of common stock, which causes us to be deemed a “controlled company” under the rules of the NYSE. In addition, Innoviva’s interests in our business may be different than our other stockholders.

RISK FACTORS

Investing in our securities involves a high degree of risk. Prior to making a decision about investing in our securities, you should carefully consider the specific risk factors discussed in the sections entitled “Risk Factors” contained in our annual report on Form 10-K for the fiscal year ended December 31, 2024 under the heading “Item 1A. Risk Factors,” and as described or may be described in any subsequent quarterly report on Form 10-Q under the heading “Item 1A. Risk Factors,” as well as in any applicable prospectus supplement and contained or to be contained in our filings with the SEC and incorporated by reference in this prospectus, together with all of the other information contained in this prospectus, or any applicable prospectus supplement. For a description of these reports and documents, and information about where you can find them, see “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.” If any of the risks or uncertainties described in our SEC filings or any prospectus supplement or any additional risks and uncertainties actually occur, our business, financial condition and results of operations could be materially and adversely affected.

In that case, the trading price of our securities could decline and you might lose all or part of the value of your investment.

THE SECURITIES WE MAY OFFER

We may offer up to $100,000,000 of shares of our common stock, preferred stock, debt securities, warrants or units in any combination of the foregoing, under this prospectus at prices and on terms to be determined by market conditions at the time of offering. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities.

A prospectus supplement and any related free writing prospectus that we may authorize to be provided to you also may add, update or change information contained in this prospectus or in documents we have incorporated by reference.

This prospectus may not be used to offer or sell securities unless it is accompanied by a prospectus supplement.

We may sell the securities directly to or through agents, underwriters or dealers. We, and our agents, dealers or underwriters, reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities through agents or underwriters, we will include in the applicable prospectus supplement:

the name of those agents or underwriters;

applicable fees, discounts and commissions to be paid to them;

details regarding options to purchase additional securities, if any; and

the net proceeds to us.

Common Stock.

We may issue shares of our common stock from time to time. Holders of our common stock are entitled to one vote per share on all matters submitted to a vote of shareholders. Subject to any preferences of any of our preferred stock that may be outstanding, holders of our common stock are entitled to dividends when and if declared by our board of directors.

Preferred Stock.

Our board of directors has the authority, subject to limitations prescribed by Washington law, to issue preferred stock in one or more series, to establish from time to time the number of shares to be included in each series, and to fix or alter the rights, preferences and privileges of the preferred stock, along with any limitations or restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences of each class or series of preferred stock.

Each series of preferred stock, if issued, will be more fully described in the particular prospectus supplement that will accompany this prospectus, including redemption provisions, rights in the event of our liquidation, dissolution or winding-up, voting rights and rights to convert into common stock.

Warrants.

We may issue warrants for the purchase of common stock or preferred stock, in one or more series, from time to time. We may issue warrants independently or together with common stock, preferred stock or debt securities, and the warrants may be attached to or separate from our common stock, preferred stock or debt securities. In this prospectus, we have summarized certain general features of the warrants. We urge you, however, to read the applicable prospectus supplement (and any free writing prospectus that we may authorize to be provided to you) related to the particular series of warrants being offered, as well as the complete warrant agreement and warrant certificate that contain the terms of the warrants. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant agreement, including a form of warrant certificate, that describes the terms of the particular series of warrants we are offering before the issuance of the related series of warrants.

We will evidence each series of warrants by warrant certificates that we will issue. Warrants may be issued under an applicable warrant agreement that we enter into with a warrant agent. We will indicate the name and address of the warrant agent, if applicable, in the prospectus supplement relating to the particular series of warrants being offered.

Debt Securities.

We may offer secured or unsecured obligations in the form of one or more series of debt securities, which may be senior, senior subordinated or subordinated obligations. Any subordinated debt securities generally will be entitled to payment only after payment of our senior debt. Senior debt generally includes all debt for money borrowed by us, except debt that is stated in the instrument governing the terms of that debt to be not senior to, or to have the same rank in right of payment as, or to be expressly junior to, the subordinated debt securities. We may issue debt securities that are convertible into shares of our common stock or preferred stock.

The debt securities will be issued under an indenture, as supplemented by a resolution of our board of directors, an officer’s certificate or a supplemental indenture, between us and a trustee. We have summarized the general features of the debt securities to be governed by the indenture. The indenture has been filed as an exhibit to the registration statement of which this prospectus forms a part. We encourage you to read the indenture. Instructions on how you can get copies of this document are provided under the heading “Where You Can Find More Information.”

Units

We may issue units comprised of one or more of the other classes of securities issued by us as described in this prospectus in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference herein contain forward-looking statements. The forward-looking statements are contained principally in the sections entitled “Prospectus Summary” and “Risk Factors” in this prospectus or the documents incorporated herein by reference. These statements relate to future events or to our future financial performance and involve known and unknown risks, uncertainties and other factors which may cause our actual results, performance or events to be materially different from any future results, performance or events expressed or implied by the forward-looking statements. Forward-looking statements include, but are not limited to, statements regarding:

our estimates regarding anticipated operating losses, capital requirements and needs for additional funds;

our ability to raise additional capital when needed and to continue as a going concern;

our ability to manufacture, or otherwise secure the manufacture of, sufficient amounts of our product candidates for our preclinical studies and clinical trials;

our clinical development plans, including planned clinical trials;

our research and development plans;

our ability to select combinations of phages to formulate our product candidates;

our development of bacteriophage-based therapies;

the potential use of bacteriophages to treat bacterial infections;

the potential future of antibiotic resistance;

the ability for bacteriophage therapies to disrupt and destroy biofilms and restore sensitivity to antibiotics;

the potential for bacteriophage technology being uniquely positioned to address the global threat of antibiotic resistance;

our planned development strategy, presenting data to regulatory agencies and defining planned clinical studies;

the expected timing of additional clinical trials, including Phase 1b/Phase 2 or registrational clinical trials;

our ability to manufacture and secure sufficient quantities of our product candidates for clinical trials;

the drug product candidates to be supplied by us for clinical trials;

the safety and efficacy of our product candidates;

our anticipated regulatory pathways for our product candidates;

the activities to be performed by specific parties in connection with clinical trials;

our ability to successfully complete preclinical and clinical development of, and obtain regulatory approval of our product candidates and commercialize any approved products on our expected timeframes or at all;

our pursuit of additional indications;

the content and timing of submissions to and decisions made by the FDA and other regulatory agencies;

our ability to leverage the experience of our management team and to attract and retain management and other key personnel;

the capacities and performance of our suppliers, manufacturers, contract research organizations and other third parties over whom we have limited control;

our ability to staff and maintain our Los Angeles production facility under fully compliant cGMP;

the actions of our competitors and success of competing drugs or other therapies that are or may become available;

our expectations with respect to future growth and investments in our infrastructure, and our ability to effectively manage any such growth;

the size and potential growth of the markets for any of our product candidates, and our ability to capture share in or impact the size of those markets;

the benefits of our product candidates;

the potential market growth and market and industry trends;

maintaining collaborations with third parties including our partnerships with the CFF and the DoD;

potential future collaborations with third parties and the potential markets and market opportunities for product candidates;

our ability to achieve our vision, including improvements through engineering and success of clinical trials;

our ability to meet anticipated milestones in the development and testing of the relevant product;

our ability to be a leader in the development of phage-based therapeutics;

the expected use of proceeds from the $26.2 million DoD award;

the effects of government regulation and regulatory developments, and our ability and the ability of the third parties with whom we engage to comply with applicable regulatory requirements;

the accuracy of our estimates regarding future expenses, revenues, capital requirements and need for additional financing;

our expectations regarding future planned expenditures;

our ability to achieve and maintain effective internal control over financial reporting in accordance with Section 404 of the Sarbanes-Oxley Act;

our ability to obtain, maintain and successfully enforce adequate patent and other intellectual property protection of any of our products and product candidates;

our ability to protect our intellectual property, including pending and issued patents;

our ability to operate our business without infringing the intellectual property rights of others;

our ability to advance our clinical development programs;

the effects of ongoing conflicts between Ukraine and Russia and in the Middle East, the recent and potential future bank failures or other geopolitical events;

the potential economic and regulatory impacts on the biotechnology, pharmaceutical and drug manufacturing industries;

the effects of artificial intelligence on our business and the industry as a whole; and

statements of belief and any statement of assumptions underlying any of the foregoing.

In some cases, you can identify these statements by terms such as “anticipate,” “believe,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “will,” “would” or the negative of those terms, and similar expressions. These forward-looking statements reflect our management’s beliefs and views with respect to future events and are based on estimates and assumptions as of the date of this prospectus and are subject to risks and uncertainties. Moreover, we operate in a very competitive and rapidly changing environment. New risks emerge from time to time. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this prospectus, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain. Given these uncertainties, you should not place undue reliance on any of the forward-looking statements included in this prospectus. In addition, this prospectus also contains estimates, projections and other information concerning our industry, our business, and the markets for our product candidates, as well as data regarding market research, estimates and forecasts prepared by our management. Information that is based on estimates, forecasts, projections, market research or similar methodologies is inherently subject to uncertainties and actual events or circumstances may differ materially from events and circumstances reflected in this information. These statements are based upon information available to us as of the date hereof, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information.

You should carefully read this prospectus, the documents that we incorporate by reference into this prospectus and the documents we reference in this prospectus and have filed as exhibits to the registration statement, of which this prospectus is a part, completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in this prospectus by these cautionary statements.

Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to update the reasons actual results could differ materially from those anticipated in any forward-looking statements, whether as a result of new information, future events or otherwise.

USE OF PROCEEDS

Except as described in any prospectus supplement or in any related free writing prospectus that we may authorize to be provided to you, we currently intend to use the net proceeds from the sale of securities under this prospectus for general corporate purposes, including manufacturing expenses, clinical trial expenses, research and development expenses and general and administrative expenses. We may also use a portion of the net proceeds to in-license, invest in or acquire businesses or technologies that we believe are complementary to our own, although we have no current plans, commitments or agreements with respect to any acquisitions. As of the date of this prospectus, we cannot specify with certainty all of the particular uses of the proceeds from the sale of securities under this prospectus. Accordingly, we will retain broad discretion over the use of such proceeds. Pending the use of the net proceeds from the sale of securities under this prospectus as described above, we intend to invest the net proceeds in investment-grade, interest-bearing instruments.

DESCRIPTION OF CAPITAL STOCK

Our articles of incorporation authorize us to issue up to 217,000,000 shares of common stock, par value $0.01 per share, and 10,000,000 shares of preferred stock, par value $0.01 per share. As of August 11, 2025, we had 36,229,842 shares of common stock outstanding and no shares of preferred stock outstanding.

The following summary description of our capital stock is based on the provisions of our articles of incorporation and bylaws and the applicable provisions of the Washington Business Corporation Act (“WBCA”). This information is qualified entirely by reference to the applicable provisions of our articles of incorporation, bylaws and the WBCA. For information on how to obtain copies of our articles of incorporation and bylaws, which are exhibits to the registration statement of which this prospectus is a part, see “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

Common Stock

Voting

Our common stock is entitled to one vote for each share held on all matters submitted to a vote of the shareholders, including the election of directors, except for matters that are voted on exclusively by a separate class or series of our shareholders and not by the holders of common stock, and does not have cumulative voting rights. Accordingly, the holders of a majority of the shares of our common stock entitled to vote in any election of directors can elect all of the directors standing for election.

Dividends

Subject to preferences that may be applicable to any then-outstanding preferred stock, the holders of common stock are entitled to receive dividends, if any, as may be declared from time to time by our board of directors out of legally available funds.

Liquidation

In the event of our liquidation, dissolution or winding-up, holders of our common stock will be entitled to share ratably in the net assets legally available for distribution to shareholders after the payment of all our debts and other liabilities, subject to the satisfaction of any liquidation preference granted to the holders of any outstanding shares of preferred stock.

Rights and Preferences

Holders of our common stock have no preemptive, conversion or subscription rights, and there is no redemption or sinking fund provisions applicable to our common stock. The rights, preferences and privileges of the holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of our preferred stock that are outstanding or that we may designate and issue in the future.

Fully Paid and Nonassessable

All of our outstanding shares of common stock are, and the shares of common stock to be issued in any offering under this prospectus will be, fully paid and nonassessable.

Preferred Stock

Our board of directors has the authority, without further action by the shareholders, to issue up to 10,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each such series, to fix the rights, preferences and privileges of the shares of each wholly unissued series and any qualifications, limitations or restrictions thereon and to increase or decrease the number of shares of any such series, but not below the number of shares of such series then outstanding.

Our board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of the common stock. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring or preventing a change in our control that may otherwise benefit holders of our common stock and may adversely affect the market price of the common stock and the voting and other rights of the holders of common stock.

There currently are no provisions under our amended and restated articles of incorporation or under any other contractual obligations whereby we are required to issue or sell shares of preferred stock and we have no present plans to issue any shares of preferred stock.

Anti-Takeover Effects of Provisions of Our Articles of Incorporation, Our Bylaws and Washington Law

Provisions in our articles of incorporation, our bylaws and under Washington law may delay or prevent an acquisition of us or a change in our management, including transactions in which shareholders might otherwise receive a premium for their shares or transactions that our shareholders might otherwise deem to be in their best interests. Certain of the provisions of our articles of incorporation and bylaws with an anti-takeover effect are summarized below. These provisions may frustrate or prevent any attempts by our shareholders to replace or remove our current management by making it difficult for shareholders to replace members of our board of directors, which is responsible for appointing the members of our management.

Additionally, because we are incorporated in Washington, we are governed by the provisions of Chapter 23B.19 of the WBCA, which, among other things, prohibits a “target corporation,” with certain exceptions, from engaging in certain “significant business transactions” for a period of five years after the share acquisition by an “acquiring person”, unless (a) the significant business transaction is approved by a majority of the members of the target corporation’s board of directors prior to the time of the acquiring person’s share acquisition or (b) the significant business transaction was approved by both the majority of the members of the target corporation’s board of directors and approved at a shareholder meeting by at least two-thirds of the outstanding voting shares (excluding the acquiring person’s shares or shares over which the acquiring person has voting control) at or subsequent to the acquiring person’s share acquisition. An “acquiring person” is defined as a person or group of persons which beneficially owns 10% or more of the voting securities of the target corporation. Such significant business transactions may include, among other things:

any merger or consolidation with, disposition of assets to, or issuance or redemption of stock to or from, the acquiring person;

any termination of 5% or more of the employees of the target corporation as a result of the acquiring person’s acquisition of 10% or more of the shares; or

allowing the acquiring person to receive any disproportionate benefit as a shareholder.

After the five-year period, a significant business transaction may take place as long as it complies with certain fair price provisions of the statute or is approved by a majority of the votes entitled to be counted within each voting group entitled to vote separately on the transaction (excluding the acquiring person’s shares or shares over which the acquiring person has voting control) at an annual or special meeting of shareholders.

Articles of Incorporation and Bylaws

The provisions of our articles of incorporation and bylaws may delay or discourage transactions involving an actual or potential change in our control or change in our management, including transactions in which shareholders might otherwise receive a premium for their shares or transactions that our shareholders might otherwise deem to be in their best interests. Therefore, these provisions could adversely affect the price of our common stock. Among other things, our articles of incorporation and bylaws, as applicable:

permit our board of directors to issue up to 10,000,000 shares of preferred stock, with any rights, preferences and privileges as they may designate (including the right to approve an acquisition or other change in our control);

provide that shareholders seeking to present proposals before a meeting of shareholders or to nominate candidates for election as directors at a meeting of shareholders must provide advance notice in writing in a timely manner and also specify requirements as to the form and content of a shareholder’s notice;

provide that directors may be removed only for cause by the holders of not less than two-thirds of the shares entitled to elect the director or directors whose removal is sought;

require the vote of the holders of at least two-thirds of the issued and outstanding shares to amend or repeal certain provisions of our articles of incorporation;

require the vote of the holders of at least two-thirds of the issued and outstanding shares to approve a “Business Combination” (as defined in our articles of incorporation) that is not approved by the “Continuing Directors”;

require the approval of a majority of the Continuing Directors to adopt, amend or repeal the bylaws that may be amended or repealed by the board of directors and require the approval of the holders of not less than two-thirds of the outstanding shares to adopt, amend or repeal our bylaws; and

does not provide for cumulative voting rights.

NYSE American Listing

Our common stock is listed on the NYSE American under the symbol “ARMP.”

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A. The transfer agent and registrar’s address is 150 Royall Street, Canton, MA 02021.

DESCRIPTION OF THE DEBT SECURITIES

As of the date of this prospectus, we have no debt securities issued and outstanding.

The following description, together with the additional information we include in any applicable prospectus supplement, summarizes the material terms and provisions of the debt securities that we may offer under this prospectus. While the terms we have summarized below will apply generally to any future debt securities we may offer, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement. The terms of any debt securities we offer under a prospectus supplement may differ from the terms we describe below.

We will issue notes under an indenture, which we will enter into with the trustee named in the indenture. Any indenture will be qualified under the Trust Indenture Act of 1939. You should read the summary below, the applicable prospectus supplement and the provisions of the applicable indenture and any related security documents, if any, in their entirety before investing in our debt securities.

We will describe in each prospectus supplement the following terms relating to a series of debt securities:

the title;

the principal amount being offered, and if a series, the total amount authorized and the total amount outstanding;

any limit on the amount that may be issued;

whether or not we will issue the series of debt securities in global form, and if so, the terms and who the depository will be;

the maturity date;

the principal amount due at maturity, and whether the debt securities will be issued with an original issue discount;

whether and under what circumstances, if any, we will pay additional amounts on any debt securities held by a person who is not a United States person for tax purposes, and whether we can redeem the debt securities if we have to pay such additional amounts;

the annual interest rate, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

the terms of the subordination of any series of subordinated debt;

the place where payments will be payable;

restrictions on transfer, sale or other assignment, if any;

our right, if any, to defer payment of interest and the maximum length of any such deferral period;

the date, if any, after which the conditions upon which, and the price at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemptions provisions;

the date, if any, on which, and the price at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder’s option to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

whether the indenture will restrict our ability to pay dividends, or will require us to maintain any asset ratios or reserves;

whether we will be restricted from incurring any additional indebtedness, issuing additional securities, or entering into a merger, consolidation or sale of our business;

a discussion of any material or special United States federal income tax considerations applicable to the debt securities;

information describing any book-entry features;

provisions for a sinking fund purchase or other analogous fund, if any;

any provisions for payment of additional amounts for taxes and any provision for redemption, if we must pay such additional amount with respect to any debt security;

whether the debt securities are to be offered at a price such that they will be deemed to be offered at an “original issue discount” as defined in paragraph (a) of Section 1273 of the Internal Revenue Code;

the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;

the terms on which a series of debt securities may be convertible into or exchangeable for our common stock, any other of our securities or securities of a third party, and whether conversion or exchange is mandatory, at the option of the holder or at our option;

events of default;

whether we and/or the debenture trustee may change an indenture without the consent of any holders;

the form of debt security and how it may be exchanged and transferred;

descriptions of the debenture trustee and paying agent, and the method of payments; and

any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, including any additional events of default or covenants provided with respect to the debt securities, and any terms which may be required by us or advisable under applicable laws or regulations.

Specific indentures will contain additional important terms and provisions and will be incorporated by reference as an exhibit to the registration statement that includes this prospectus, or as an exhibit to a report filed under the Exchange Act, incorporated by reference in this prospectus.

DESCRIPTION OF WARRANTS

We may issue warrants for the purchase of common stock or preferred stock, in one or more series. We may issue warrants independently or together with common stock, preferred stock or debt securities, and the warrants may be attached to or separate from our common stock, preferred stock or debt securities. While the terms summarized below will apply generally to any warrants that we may offer, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. The terms of any warrants offered under a prospectus supplement may differ from the terms described below.

We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant agreement, including a form of warrant certificate, that describes the terms of the particular series of warrants we are offering before the issuance of the related series of warrants. The following summaries of material provisions of the warrants and the warrant agreements are subject to, and qualified in their entirety by reference to, all the provisions of the warrant agreement and warrant certificate applicable to the particular series of warrants that we may offer under this prospectus. We urge you to read the applicable prospectus supplements related to the particular series of warrants that we may offer under this prospectus, as well as any related free writing prospectuses, and the complete warrant agreements and warrant certificates that contain the terms of the warrants.

General

We will describe in the applicable prospectus supplement the terms of the series of warrants being offered, including:

the offering price and aggregate number of warrants offered;

the currency for which the warrants may be purchased;

if applicable, the number of warrants issued with each share of common stock or preferred stock, or with the principal amount of any debt security;

if applicable, the date on and after which the warrants and the related shares will be separately transferable;

the number of shares of common stock or preferred stock purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;

the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreements and the warrants;

the terms of any rights to redeem or call the warrants;

any provisions for changes to or adjustments in the exercise price or number of shares issuable upon exercise of the warrants;

the dates on which the right to exercise the warrants will commence and expire;

the manner in which the warrant agreements and warrants may be modified; and

any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

Before exercising their warrants, holders of warrants will not have any of the rights of holders of common stock or preferred stock purchasable upon such exercise, including the right to receive dividends, if any, or payments upon our liquidation, dissolution or winding up, or to exercise voting rights.

Exercise of Warrants

Each warrant will entitle the holder to purchase the number of shares of common stock or preferred stock that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. Unless we otherwise specify in the applicable prospectus supplement, holders of the warrants may exercise the warrants at any time up to the specified time on the expiration date that we set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

Holders of the warrants may exercise the warrants by delivering the warrant certificate representing the warrants to be exercised together with specified information, and paying the required amount to the warrant agent in immediately available funds, as provided in the applicable prospectus supplement. We will set forth on the reverse side of the warrant certificate and in the applicable prospectus supplement the information that the holder of the warrant will be required to deliver to the warrant agent.

Upon receipt of the required payment and the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement, we will issue and deliver the shares purchasable upon such exercise. If fewer than all of the warrants represented by the warrant certificate are exercised, then we will issue a new warrant certificate for the remaining amount of warrants. If we so indicate in the applicable prospectus supplement, holders of the warrants may surrender securities as all or part of the exercise price for warrants.

Governing Law

Unless we provide otherwise in the applicable prospectus supplement, the warrants and warrant agreements will be governed by and construed in accordance with the laws of the State of New York.

Enforceability of Rights by Holders of Warrants

Each warrant agent will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.

DESCRIPTION OF UNITS

We may issue units comprised of one or more of the other classes of securities described in this prospectus in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The units may be issued under unit agreements to be entered into between us and a unit agent, as detailed in the prospectus supplement relating to the units being offered. The prospectus supplement will describe:

the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances the securities comprising the units may be held or transferred separately;

a description of the terms of any unit agreement governing the units;

a description of the provisions for the payment, settlement, transfer or exchange of the units;

a discussion of material federal income tax considerations, if applicable; and

whether the units if issued as a separate security will be issued in fully registered or global form.

The descriptions of the units in this prospectus and in any prospectus supplement are summaries of the material provisions of the applicable unit agreements. These descriptions do not restate those unit agreements in their entirety and may not contain all the information that you may find useful. We urge you to read the applicable unit agreements because they, and not the summaries, define your rights as holders of the units. For more information, please review the forms of the relevant unit agreements, which will be filed with the SEC promptly after the offering of units and will be available as described in the section titled “Where You Can Find More Information.”

LEGAL OWNERSHIP OF SECURITIES

We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depository or warrant agent maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities.

As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a book-entry security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not holders, of the securities.

Street Name Holders

We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in “street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so.

Special Considerations for Indirect Holders

If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your bank, broker or other financial institution to find out:

how it handles securities payments and notices;

whether it imposes fees or charges;

how it would handle a request for the holders’ consent, if ever required;

whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;

how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and

if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.

Global Securities

A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, the Depository Trust Company (“DTC”), will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under “Special Situations When a Global Security Will Be Terminated.” As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a holder of the security, but only an indirect holder of a beneficial interest in the global security.

If the prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations for Global Securities

As an indirect holder, an investor’s rights relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

If securities are issued only in the form of a global security, an investor should be aware of the following:

An investor cannot cause the securities to be registered in his or her name and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below.

An investor will be an indirect holder and must look to his or her own bank, broker or other financial institution for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above.

An investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form.

An investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective.

The depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in a global security. We and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in a global security. We and the trustee also do not supervise the depositary in any way.

The depositary may, and we understand that DTC will, require that those who purchase and sell interests in a global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well.

Financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities. There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When a Global Security Will Be Terminated

In a few special situations described below, the global security will terminate, and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks, brokers or other financial institutions to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

The global security will terminate when the following special situations occur:

if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;

if we notify any applicable trustee that we wish to terminate that global security; or

if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

The applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

PLAN OF DISTRIBUTION

We may sell our securities covered by this prospectus in any of three ways (or in any combination):

to or through underwriters or dealers;

directly to one or more purchasers; or

through agents.

We may distribute the securities:

from time to time in one or more transactions at a fixed price or prices, which may be changed from time to time;

“at the market” offerings, as defined in Rule 415 under the Securities Act of 1933, as amended, (the “Securities Act”), at negotiated prices, at prices prevailing at the time of sale or at prices related to such prevailing market prices, including sales made directly on a national securities exchange or sales made through a market maker other than on an exchange or other similar offerings through sales agents; or

at negotiated prices.

Each time we offer and sell securities covered by this prospectus, we will provide a prospectus supplement or supplements that will describe the method of distribution and set forth the terms of the offering, including:

the name or names of any underwriters, dealers or agents;

the amounts of securities underwritten or purchased by each of them;

the purchase price of securities and the proceeds we will receive from the sale;

any option under which underwriters may purchase additional securities from us;

any underwriting discounts or commissions or agency fees and other items constituting underwriters’ or agents’ compensation;

the public offering price of the securities;

any discounts, commissions or concessions allowed or reallowed or paid to dealers; and

any securities exchange or market on which the securities may be listed.

Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may be changed from time to time. We may determine the price or other terms of the securities offered under this prospectus by use of an electronic auction. We will describe how any auction will determine the price or any other terms, how potential investors may participate in the auction and the nature of the obligations of the underwriter, dealer or agent in the applicable prospectus supplement.

Underwriters or dealers may offer and sell the offered securities from time to time in one or more transactions, including negotiated transactions, at a fixed public offering price or at varying prices determined at the time of sale. If underwriters or dealers are used in the sale of any securities, the securities will be acquired by the underwriters or dealers for their own account and may be resold from time to time in one or more transactions described above. The securities may be either offered to the public through underwriting syndicates represented by managing underwriters, or directly by underwriters or dealers. Generally, the underwriters’ or dealers’ obligations to purchase the securities will be subject to certain conditions precedent. The underwriters or dealers will be obligated to purchase all of the securities if they purchase any of the securities, unless otherwise specified in the prospectus supplement. We may use underwriters with whom we have a material relationship. We will describe the nature of any such relationship in the prospectus supplement, naming the underwriter.

We may sell the securities through agents from time to time. The prospectus supplement will name any agent involved in the offer or sale of the securities and any commissions we pay to them. Generally, any agent will be acting on a best efforts basis for the period of its appointment. We may authorize underwriters, dealers or agents to solicit offers by certain purchasers to purchase the securities from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. The contracts will be subject only to those conditions set forth in the prospectus supplement, and the prospectus supplement will set forth any commissions we pay for solicitation of these contracts.

Agents, dealers and underwriters may be entitled to indemnification by us against certain civil liabilities, including liabilities under the Securities Act, or to contribution with respect to payments which the agents, dealers or underwriters may be required to make in respect thereof. Agents, dealers and underwriters may engage in transactions with, or perform services for us in the ordinary course of business.

All securities we may offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities.

Any underwriter may engage in over-allotment, stabilizing transactions, short covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. Over-allotment involves sales in excess of the offering size, which create a short position. This short sales position may involve either “covered” short sales or “naked” short sales. Covered short sales are short sales made in an amount not greater than the underwriters’ over-allotment option to purchase additional securities in the relevant offering. The underwriters may close out any covered short position either by exercising their over-allotment option or by purchasing securities in the open market. To determine how they will close the covered short position, the underwriters will consider, among other things, the price of securities available for purchase in the open market, as compared to the price at which they may purchase securities through the over-allotment option. Naked short sales are short sales in excess of the over-allotment option. The underwriters must close out any naked short position by purchasing securities in the open market. A naked short position is more likely to be created if the underwriters are concerned that, in the open market after pricing, there may be downward pressure on the price of the securities that could adversely affect investors who purchase securities in the offering. Stabilizing transactions permit bids to purchase the underlying security for the purpose of fixing the price of the security so long as the stabilizing bids do not exceed a specified maximum. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a covering transaction to cover short positions.

Any underwriters who are qualified market makers on the NYSE American may engage in passive market making transactions in our common stock, preferred stock, warrants and debt securities, as applicable on the NYSE American in accordance with Rule 103 of Regulation M, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the securities. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded.

Similar to other purchase transactions, an underwriter’s purchase to cover the syndicate short sales or to stabilize the market price of our securities may have the effect of raising or maintaining the market price of our securities or preventing or mitigating a decline in the market price of our securities. As a result, the price of our securities may be higher than the price that might otherwise exist in the open market. The imposition of a penalty bid might also have an effect on the price of the securities if it discourages resales of the securities.

Neither we nor any underwriter makes any representation or prediction as to the effect that the transactions described above may have on the price of the securities. If such transactions are commenced, they may be discontinued without notice at any time.

LEGAL MATTERS

The validity of the securities being offered by this prospectus will be passed upon for us by Willkie Farr & Gallagher LLP, New York, New York, and Ballard Spahr LLP, Seattle, Washington.

EXPERTS

Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2024, as set forth in their report (which contains an explanatory paragraph describing conditions that raise substantial doubt about Armata Pharmaceuticals, Inc.’s ability to continue as a going concern as described in Note 2 to the consolidated financial statements) which is incorporated by reference in this prospectus and elsewhere in the registration statement. Our consolidated financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on Form S-3 under the Securities Act, with respect to the securities being offered by this prospectus. This prospectus does not contain all of the information in the registration statement and its exhibits. For further information with respect to us and the securities offered by this prospectus, we refer you to the registration statement and its exhibits. Statements contained in this prospectus as to the contents of any contract or any other document referred to are not necessarily complete, and in each instance, we refer you to the copy of the contract or other document filed as an exhibit to the registration statement. Each of these statements is qualified in all respects by this reference. The SEC maintains a website that contains reports, proxy statements, and other information about registrants, like us, that file electronically with the SEC. The address of that website is www.sec.gov. The information contained in, or that can be accessed through, the SEC’s website is not incorporated by reference in, and is not part of, this prospectus or any prospectus supplement.

We are subject to the information and periodic reporting requirements of the Exchange Act, and we file periodic reports, proxy statements and other information with the SEC. We maintain a website at https://www.armatapharma.com/. You may access our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act with the SEC free of charge at our website as soon as reasonably practicable after such material is electronically filed with, or furnished to, the SEC. The information contained in, or that can be accessed through, our website is not incorporated by reference in, and is not part of, this prospectus.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is an important part of this prospectus. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus, while information that we file later with the SEC will automatically update and supersede the information in this prospectus to the extent that a statement contained in this prospectus or free writing prospectus provided to you in connection with this offering, or in any other document we subsequently file with the SEC that also is incorporated by reference in this prospectus, modifies or supersedes the original statement.

The following documents, which we have filed with the SEC are incorporated by reference in this prospectus:

our Annual Report on Form 10-K for the fiscal year ended December 31, 2024, filed with the SEC on March 20, 2025;

our quarterly reports on Form 10-Q for the quarters ended March 31, 2025 and June 30, 2025 filed with the SEC on May 14, 2025 and August 12, 2025, respectively;

our Current Reports on Form 8-K, filed with the SEC on March 12, 2025, April 2, 2025, May 1, 2025, June 13, 2025, and August 12, 2025 (only with respect to information filed under items 1.01, 2.03 and 9.01);

the portions of our Definitive Proxy Statement on Schedule 14A that are deemed to have been “filed” with the SEC on April 28, 2025;

the description of our common stock contained in our registration statement on Form 8-A, filed with the SEC on August 18, 2015, including all amendments and reports filed for the purpose of updating such description.

All documents subsequently filed by us pursuant to Sections 13(a), 13(c), 14, and 15(d) of the Exchange Act after the date of this prospectus and prior to the termination of all offerings covered by this prospectus hereby shall be deemed to be incorporated by reference in this prospectus and to be part hereof from the date of filing of such documents; provided, however, that documents or information deemed to have been furnished and not filed in accordance with SEC rules shall not be deemed incorporated by reference into this prospectus.

Any statement contained herein or in a document, all or a portion of which is incorporated or deemed to be incorporated by reference herein, shall be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained herein or in any other subsequently filed document which also is or is deemed to be incorporated by reference herein modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or amended, to constitute a part of this prospectus.

We will furnish without charge to you, on written or oral request, a copy of any or all of the documents incorporated by reference, including exhibits to these documents. You should direct any requests for documents by writing us at 5005 McConnell Avenue, Los Angeles, California 90066, Attention: SVP Finance, or telephoning us at (310) 665-2928.

The SEC maintains a website that contains reports, proxy and information statements, and other information regarding issuers that file electronically with the SEC (http://www.sec.gov). In addition, we maintain a website at www.armatapharma.com/. Information contained in our website does not constitute a part of this prospectus.

PART II

INFORMATION NOT REQUIRED IN THE PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.

The following table sets forth the costs and expenses, other than the underwriting discounts and commissions, payable by the registrant in connection with the offering of the securities pursuant to this registration statement:

SEC registration fee	$	15,310
Accounting fees and expenses		*
Legal fees and expenses		*
Printing and miscellaneous expenses		*
Total	$	15,310

These fees and expenses depend on the securities offered and the number of issuances, and accordingly cannot be estimated as of the date of this prospectus.

Item 15. Indemnification of Officers and Directors.

The registrant is incorporated under the laws of the State of Washington. Under certain circumstances, Sections 23B.08.510 and 23B.08.570 of the Washington Business Corporation Act (the “WBCA”) authorize Washington corporations to indemnify directors and officers against expenses and liabilities incurred in legal proceedings in which they are involved by reason of being a director or officer, as applicable. Under certain circumstances, Sections 23B.08.520 and 23B.08.570 obligate Washington corporations to indemnify directors and officers against reasonable expenses incurred in legal proceedings in which they are involved by reason of being a director or officer, as applicable. Sections 23B.08.560 and 23B.08.570 of the WBCA authorizes a Washington corporation, if authorized by its articles of incorporation, by a provision in the corporation’s bylaws adopted or ratified by its shareholders, or a resolution adopted or ratified by its shareholders, to indemnify or agree to indemnify a director or officer made a party to a proceeding, or obligate itself to advance or reimburse expenses incurred in a proceeding, without regard to the limitations imposed by Sections 23B.08.510 through 23B.08.550; provided, however, that no such indemnity shall indemnify any director or officer (to the same extent as a director) from or on account of (a) acts or omissions of the director or officer finally adjudged to be intentional misconduct or a knowing violation of law, (b) conduct of the director or officer finally adjudged to be in violation of Section 23B.08.310 of the WBCA (which section relates to unlawful distributions) or (c) any transaction with respect to which it was finally adjudged that such director personally received a benefit in money, property or services to which the director was not legally entitled.

Article 11 of the registrant’s articles of incorporation, provides that, to the fullest extent that the WBCA permits the limitation or elimination of the liability of a director, a director shall not be liable to the registrant or its shareholders for monetary damages for conduct as a director. Section 10 of the registrant’s amended and restated bylaws requires the registrant to indemnify every present or former director or officer against expenses, liabilities and losses incurred in connection with serving as a director or officer, as applicable, and to advance expenses of such director or officer incurred in defending any proceeding covered by the indemnity.

The registrant maintains a policy of directors’ and officers’ liability insurance that insures the directors and officers against the cost of defense, settlement or payment of a judgment under certain circumstances. The registrant has also entered into indemnification agreements with its executive officers and directors that provide for the indemnification of directors and executive officers to the fullest extent permitted by the Washington Business Corporation Act against expenses reasonably incurred by such persons in any threatened, pending or completed action, suit, investigation or proceeding in connection with their service as (i) a director or officer or (ii) a director, officer, employee or agent of another corporation or of a partnership, joint venture, trust or other enterprise, including service with respect to employee benefit plans, at the registrant’s request. In addition, the indemnification agreements provide the registrant with the obligation to advance expenses under certain circumstances and provide for procedural protections, including a determination by a reviewing party as to whether the indemnitee is permitted to be indemnified under applicable law. In addition, the registrant acknowledges that it will be the indemnitor of first resort should the indemnitee have rights to indemnification provided by other persons.

The registrant may enter into one or more underwriting agreements which provides that the underwriters are obligated, under some circumstances, to indemnify the registrant’s directors, officers and controlling persons against specified liabilities, including liabilities under the Securities Act.

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Item 16. Exhibits

See the Exhibit Index on the page immediately following the signature page to this registration statement for a list of exhibits filed as part of this registration statement, which Exhibit Index is incorporated herein by reference.

Item 17. Undertakings

(a)

The undersigned registrant hereby undertakes:

(1)

To file, during any period in which offers or sales are being made, a post-effective amendment to this Registration Statement:

(i)

To include any prospectus required by Section 10(a)(3) of the Securities Act;

(ii)

To reflect in the prospectus any facts or events arising after the effective date of the Registration Statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the Registration Statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the SEC pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20 percent change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective Registration Statement.

(iii)

To include any material information with respect to the plan of distribution not previously disclosed in the Registration Statement or any material change to such information in the Registration Statement;

provided, however, that paragraphs (1)(i), (1)(ii) and (1)(iii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the SEC by the registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), that are incorporated by reference in the Registration Statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the Registration Statement.

(2)

That, for the purpose of determining any liability under the Securities Act, each such post-effective amendment shall be deemed to be a new Registration Statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3)

To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(5)

That, for the purpose of determining liability under the Securities Act to any purchaser:

(A)

Each prospectus filed by the registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the Registration Statement as of the date the filed prospectus was deemed part of and included in the Registration Statement; and

(B)

Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a Registration Statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii), or (x) for the purpose of providing the information required by section 10(a) of the Securities Act shall be deemed to be part of and included in the Registration Statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the Registration Statement relating to the securities in the Registration Statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof. Provided, however, that no statement made in a Registration Statement or prospectus that is part of the Registration Statement or made in a document incorporated or deemed incorporated by reference into the Registration Statement or prospectus that is part of the Registration Statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the Registration Statement or prospectus that was part of the Registration Statement or made in any such document immediately prior to such effective date;

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(6)

That, for the purpose of determining liability of the registrant under the Securities Act to any purchaser in the initial distribution of the securities: the undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to this Registration Statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(i)

Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

(ii)

Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

(iii)

The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

(iv)

Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

(b)

The undersigned registrant hereby undertakes that, for purposes of determining any liability under the Securities Act, each filing of the registrant’s annual report pursuant to section 13(a) or section 15(d) of the Exchange Act (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to section 15(d) of the Exchange Act) that is incorporated by reference in the Registration Statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(h)

Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

(i)

The undersigned registrant hereby undertakes that:

(1)

For purposes of determining any liability under the Securities Act, the information omitted from the form of prospectus filed as part of this Registration Statement in reliance upon Rule 430A and contained in the form of prospectus filed by the registrant pursuant to Rule 424(b)(l) or (4) or 497(h) under the Securities Act shall be deemed to be a part of the Registration Statement as of the time it was declared effective.

(2)

For the purpose of determining any liability under the Securities Act, each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(j)

The undersigned registrant hereby undertakes to file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of section 310 of the Trust Indenture Act (the “Act”) in accordance with the rules and regulations prescribed by the Commission under section 305(b)(2) of the Act.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Los Angeles, State of California, on August 13, 2025.

	ARMATA PHARMACEUTICALS, INC.

	By:	/s/ Deborah L. Birx, M.D.
		Deborah L. Birx, M.D.
		Chief Executive Officer

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POWER OF ATTORNEY

KNOW ALL BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints Deborah L. Birx and David House, and each of them, as his or her true and lawful attorneys-in-fact and agents, each with the full power of substitution, for him or her and in his or her name, place or stead, in any and all capacities, to sign any and all amendments to this registration statement (including post-effective amendments), and to sign any registration statement for the same offering covered by this registration statement that is to be effective upon filing pursuant to Rule 462(b) promulgated under the Securities Act, and all post-effective amendments thereto, and to file the same, with exhibits thereto and other documents in connection therewith, with the U.S. Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities and on the dates indicated.

Signature	Title	Date

/s/ Deborah L. Birx, M.D.	Chief Executive Officer and	August 13, 2025
Deborah L. Birx, M.D.	Member of the Board of Directors
	(Principal Executive Officer)

/s/ David House	Senior Vice President, Finance	August 13, 2025
David House	(Principal Financial and Accounting Officer)

/s/ Robin C. Kramer	Chairman of the Board of Directors	August 13, 2025
Robin C. Kramer

/s/ Jules Haimovitz	Member of the Board of Directors	August 13, 2025
Jules Haimovitz

/s/ Odysseas D. Kostas, M.D.	Member of the Board of Directors	August 13, 2025
Odysseas D. Kostas, M.D.

/s/ Joseph M. Patti, Ph.D.	Member of the Board of Directors	August 13, 2025
Joseph M. Patti, Ph.D.

/s/ Todd C. Peterson, Ph.D.	Member of the Board of Directors	August 13, 2025
Todd C. Peterson, Ph.D.

/s/ Sarah J. Schlesinger, M.D.	Member of the Board of Directors	August 13, 2025
Sarah J. Schlesinger, M.D.

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EXHIBIT INDEX

Exhibit Number		Description of Document
1.1^		Form of Underwriting Agreement
4.1		Amended and Restated Articles of Incorporation of the Company, as amended (incorporated by reference to Exhibit 3.1 to the Company’s Quarterly Report on Form 10-Q, filed with the SEC on November 16, 2015).
4.2		Articles of Amendment to Articles of Incorporation of the Company (incorporated by reference to Exhibit 3.1 to the registrant’s Current Report on Form 8-K (File No. 001-37544), filed with the SEC on April 24, 2017).
4.3		Articles of Amendment to Articles of Incorporation of the Company (incorporated by reference to Exhibit 3.2 to the Company’s Quarterly Report on Form 10-Q, filed on November 8, 2018).
4.4		Articles of Amendment to Amended and Restated Articles of Incorporation of the registrant (incorporated by reference to Exhibit 3.1 to the Current Report on Form 8-K (File No. 001-37544), filed with the SEC on May 10, 2019).
4.5		Articles of Merger, dated as of May 9, 2019 (incorporated by reference to Exhibit 3.2 to the Current Report on Form 8-K (File No. 001-37544), filed with the SEC on May 10, 2019).
4.6		Articles of Amendment to Articles of Incorporation of the registrant, dated as of December 10, 2019 (incorporated herein by reference to Exhibit 3.1 to the Current Report on Form 8-K (File No. 001-37544), filed with the SEC on December 11, 2019).
4.7		Articles of Amendment to Articles of Incorporation of the Company (effective March 26, 2020) (incorporated herein by reference to Exhibit 3.1 to the Current Report on Form 8-K (File No. 001-37544), filed with the SEC on March 30, 2020).
4.8		Amended and Restated Bylaws of the registrant (incorporated by reference to Exhibit 3.5 to the Quarterly Report on Form 10-Q (File No. 001-37544), filed with the SEC on August 14, 2019).
4.9		Amendment to Amended and Restated Bylaws of the registrant (December 10, 2019) (incorporated herein by reference to Exhibit 3.2 to the Current Report on Form 8-K (File No. 001-37544), filed with the SEC on December 11, 2019).
4.10		Amendment to Amended and Restated Bylaws of the registrant (February 24, 2020) (incorporated herein by reference to Exhibit 3.1 to the Current Report on Form 8-K (File No. 001-37544), filed with the SEC on February 26, 2020).
4.11		Specimen Common Stock Certificate of the Company (incorporated by reference to Exhibit 4.1 to the Current Report on Form 8-K, filed on May 10, 2019).
4.12		Form of Indenture.
4.13^		Form of Debt Security.
4.14^		Form of Certificate of Designation.
4.15^		Form of Preferred Stock Certificate.
4.16^		Form of Warrant Agreement.
4.17^		Form of Unit Certificate.
5.1		Opinion of Ballard Spahr LLP.
5.2		Opinion of Willkie Farr & Gallagher LLP.
23.1		Consent of Ballard Spahr LLP (included in Exhibit 5.1).

23.2		Consent of Willkie Farr & Gallagher LLP (included in Exhibit 5.2).
23.3		Consent of Independent Registered Public Accounting Firm.
24.1		Power of Attorney (included on signature page).
25.1*		Form T-1 Statement of Eligibility of Trustee under the Indenture
101		Interactive Data File.
107		Filing Fee Table.

* To be filed by amendment to this registration statement.

^ To be filed by amendment or incorporated by reference in connection with the offering of a particular class or series of securities