T3 Defense Inc.

As filed with the Securities and Exchange Commission on September 3, 2026.

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORMS-1

REGISTRATION STATEMENT

UNDER THE SECURITIES ACT OF 1933

(Exact name of registrant as specified in its charter)

(646) 257-4214

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

Menachem Shalom

Chief Executive Officer

(646) 257-4214

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Robert Cohen

McDermott Will & Schulte LLP

333 SE 2nd Avenue, Suite 4500

Miami, Florida 33131

(561) 287-7096

Approximate date of commencement of proposed sale to the public:

As soon as practicable after the effective date hereof.

If any 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, check the following box. ☒

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 post-effective amendment filed pursuant to Rule 462(d) 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. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, 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.

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 the 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 which specifically states that this registration statement shall thereafter become effective in accordance with section 8(a) of the Securities Act of 1933 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. The selling stockholder may not sell these securities until the registration statement filed with the 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 or jurisdiction where the offer or sale is not permitted.

PRELIMINARY PROSPECTUS

SUBJECT TO COMPLETION, DATED SEPTEMBER 3, 2026

Up to 10,000,000 Shares of Common Stock

This prospectus relates to the potential offer and sale from time to time of up to 10,000,000 shares (the “Shares”) of our common stock, par value $0.0001 per share (the “Common Stock”), of T3 Defense Inc., a Delaware corporation (the “Company” or “T3”) by Esousa Group Holdings, LLC (the “Selling Stockholder” or “Esousa”). See “Selling Stockholder” for more information about the Selling Stockholder. The shares of Common Stock to which this prospectus relates will or may be issued by us to the Selling Stockholder pursuant to a common stock purchase agreement dated September 19, 2025 (the “Purchase Agreement”). Under the applicable rules of The Nasdaq Stock Market LLC (“Nasdaq”), in no event may we issue to the Selling Stockholder shares of our Common Stock representing more than 19.99% of the total number of shares of Common Stock outstanding immediately prior to the execution of the Purchase Agreement, unless we obtain the approval of the issuance of such shares by our stockholders in accordance with the applicable stock exchange rules, which we obtained at a special meeting of stockholders held on December 16, 2025 (the “Special Meeting”). See the section entitled “Esousa Committed Equity Financing” for a description of the Purchase Agreement and the transactions contemplated thereby.

Such shares of Common Stock consist of shares that we may, in our sole discretion, elect to sell to the Selling Stockholder, from time to time after the date of this prospectus, pursuant to the Purchase Agreement.

The actual number of shares of our Common Stock to be issued pursuant to the terms of the Purchase Agreement will vary depending on the market price of our Common Stock on the date we elect to sell shares of our Common Stock to the Selling Stockholder under the Purchase Agreement. Such number will not exceed the number of shares covered by this prospectus unless we file an additional registration statement under the Securities Act of 1933, as amended (the “Securities Act”), with the Securities and Exchange Commission (“SEC”).

We are not selling any shares of Common Stock being offered by this prospectus and will not receive any of the proceeds from the sale of such shares by the Selling Stockholder. However, the Purchase Agreement provides that we may sell up to an aggregate of $250,000,000 of our Common Stock (the “Purchase Shares”) to the Selling Stockholder from time to time in our discretion after the date the registration statement, of which this prospectus forms a part, is declared effective, but limited to the amount of shares covered by this prospectus, and after satisfaction of other conditions in the Purchase Agreement. As of the date of this prospectus, we have sold 360,762 Purchase Shares to the Selling Stockholder and its assignees.

The Selling Stockholder may sell or otherwise dispose of the shares of Common Stock included in this prospectus in a number of different ways and at varying prices. Although the Selling Stockholder is obligated to purchase shares of our Common Stock under the terms and subject to the conditions and limitations of the Purchase Agreement to the extent we choose to sell such shares of our Common Stock to it (subject to certain conditions), the timing and amount of any sales of Common Stock by the Selling Stockholder are within the sole discretion of the Selling Stockholder. There can be no assurances that we will choose to sell any shares of our Common Stock to the Selling Stockholder, or that the Selling Stockholder will sell any or all of the shares of our Common Stock, if any, purchased under the Purchase Agreement pursuant to this prospectus. See the section titled “Plan of Distribution” for more information about how the Selling Stockholder may sell or otherwise dispose of the Common Stock being offered in this prospectus. We will pay the expenses of registering the shares of Common Stock offered by this prospectus, but all selling and other expenses incurred by the Selling Stockholder will be paid by the Selling Stockholder. The Selling Stockholder acknowledges that it is disclosed as an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act.

On July 20, 2026, the Company effected a reverse stock split of its issued and outstanding shares of Common Stock at a ratio of 1-for-125 (the “Reverse Stock Split”). Unless noted otherwise, all share and price per share information in this prospectus for all periods presented reflect the Reverse Stock Split.

You should read this prospectus, any applicable prospectus supplement and any related free writing prospectus carefully before you invest. Our Common Stock is presently listed on the Nasdaq Global Market (“Nasdaq”) under the symbol “DFNS.” The closing price for our Common Stock on September 2, 2026, as reported by Nasdaq, was $9.26 per share.

We are an “emerging growth company” as the term is used in the Jumpstart Our Business Startups Act of 2012 and, as such, have elected to comply with certain reduced public company reporting requirements for this prospectus and future filings.

Investing in our securities involves a high degree of risk. You should carefully consider the risks and uncertainties described under the heading*“Risk Factors”* beginning on page 13 of this prospectus before making a decision to purchase our securities.

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The date of this prospectus is , 2026

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