Mercury Systems: JANA reports roughly 6.4% ownership

The percentage calculation uses Mercury Systems’ 60,863,586 shares outstanding as of September 1, 2026.

Available on EDGAR 11/10/2026 - 09:00 PM EST Accepted by SEC EDGAR 11/10/2026 - 09:00 PM EST Learn about SEC filing dates

Rhea-AI Filing Summary

Mercury Systems Inc. disclosed that JANA Partners Management, LP may be deemed to beneficially own 3,880,671 shares, approximately 6.4% of the company’s outstanding shares. The reported amount includes 9,542 deferred stock units granted to Mr. Ostfeld for board service; rights to shares issuable under the award were assigned to JANA.

The shares were acquired at an aggregate purchase price of approximately $118 million. On November 10, 2026, JANA filed for early termination under the Hart-Scott-Rodino Act in light of the pending expiration of an existing antitrust clearance. JANA reported no share transactions during the preceding 60 days.

Filing Explained

JANA says the shares are held in commingled margin accounts that may extend credit, with the positions pledged against account debits; because other securities are held there, the filing cannot identify how much margin, if any, funded the $118 million purchase.

Key Figures

Beneficially owned shares: 3,880,671 shares Beneficial ownership: Approximately 6.4% Aggregate purchase price: Approximately $118 million +4 more

7 metrics

Beneficially owned shares 3,880,671 shares JANA’s reported position as of November 10, 2026

Beneficial ownership Approximately 6.4% Percentage based on shares outstanding as of September 1, 2026

Aggregate purchase price Approximately $118 million Purchase price for the reported shares

Shares outstanding 60,863,586 shares As of September 1, 2026

Deferred stock units 9,542 units Granted to Mr. Ostfeld for board service

Vested deferred stock units 7,194 units Of the 9,542 units included in the reported position

Deferred stock units granted 2,348 units Granted October 28, 2026

Key Terms

beneficially own, deferred stock units (DSUs), Hart-Scott-Rodino Antitrust Improvements Act of 1976, commingled margin accounts, +1 more

5 terms

beneficially own regulatory

"may be deemed to beneficially own 3,880,671 Shares"

Beneficially own means having the economic rights and risks of a security—such as the right to receive dividends, sell the shares, or profit from price changes—whether or not your name appears on the official share register. Think of it like renting a car: you use it and reap the benefits even if the title lists someone else. Investors care because beneficial ownership determines who truly controls value, must be disclosed under securities rules, and can signal potential influence or trading activity that affects a stock’s price.

deferred stock units (DSUs) financial

"9,542 deferred stock units ("DSUs") granted to Mr. Ostfeld"

Deferred stock units (DSUs) are a form of long-term pay that promises an employee or director future company shares or cash equal to the share value at a later date, usually after leaving the company or at a set vesting time. Think of them as a delayed paycheck tied to the stock: they align recipients’ interests with long-term share performance and matter to investors because they create potential future dilution and signal how management is rewarded and incentivized.

Hart-Scott-Rodino Antitrust Improvements Act of 1976 regulatory

"filed for early termination under the Hart-Scott-Rodino Antitrust Improvements Act of 1976"

commingled margin accounts financial

"held by the investment funds managed by JANA in commingled margin accounts"

margin borrowings financial

"investment funds in accounts managed by JANA and margin borrowings"

Margin borrowings are loans an investor takes from a brokerage using their existing cash or securities as collateral to buy additional investments. Think of it like using a down payment to borrow extra money to buy more of something: it can magnify gains if prices rise but also magnify losses, incur interest costs, and trigger forced sells if the collateral falls below required levels. Investors watch them because they increase both potential return and risk to a portfolio.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many MRCY shares does JANA report beneficially owning?

JANA Partners Management, LP may be deemed to beneficially own 3,880,671 shares, approximately 6.4% of Mercury Systems Inc. The reported percentage is based on 60,863,586 shares outstanding as of September 1, 2026.

What deferred stock units are included in JANA’s MRCY ownership?

The reported amount includes 9,542 deferred stock units granted to Mr. Ostfeld for board service: 7,194 vested units and 2,348 units granted October 28, 2026. The latter will vest on the earlier of the first anniversary of the grant date and the next annual meeting of shareholders. Mr. Ostfeld assigned to JANA all rights to shares issuable under the award.

Why did JANA file for early termination under the HSR Act?

JANA filed for early termination under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 on November 10, 2026, in light of the pending expiration of an existing antitrust clearance.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 5)

MERCURY SYSTEMS INC

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

589378108

(CUSIP Number)

Ele Klein & Brandon Gold
McDermott Will & Schulte LLP, 919 Third Avenue
New York, NY, 10022
212-756-2000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

11/10/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 589378108

1

Name of reporting person

JANA Partners Management, LP

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 3,880,671.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 3,880,671.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

3,880,671.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

6.4 %

14

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.01 per share
(b)	Name of Issuer: MERCURY SYSTEMS INC
(c)	Address of Issuer's Principal Executive Offices: 50 Minuteman Road, Andover, MASSACHUSETTS , 01810.
Item 1 Comment: This Amendment No. 5 ("Amendment No. 5") amends and supplements the statement on Schedule 13D filed with the SEC on September 22, 2022 (as amended from time to time, the "Schedule 13D") with respect to the Shares of the Issuer. This Amendment No. 5 amends Items 3, 4, and 5(a) - (c) as set forth below. Capitalized terms used herein and not otherwise defined in this Amendment No. 5 have the meanings set forth in the Schedule 13D.
Item 3.	Source and Amount of Funds or Other Consideration
	Item 3 of the Schedule 13D is hereby amended and restated in its entirety as follows: The 3,880,671 Shares reported herein as beneficially owned by JANA were acquired at an aggregate purchase price of approximately $118 million. Such Shares were acquired with investment funds in accounts managed by JANA and margin borrowings described in the following sentence. Such Shares are held by the investment funds managed by JANA in commingled margin accounts, which may extend margin credit to JANA from time to time, subject to applicable federal margin regulations, stock exchange rules and credit policies. In such instances, the positions held in the margin accounts are pledged as collateral security for the repayment of debit balances in the account. The margin accounts bear interest at a rate based upon the broker's call rate from time to time in effect. Because other securities are held in the margin accounts, it is not possible to determine the amounts, if any, of margin used to purchase the Shares reported herein.
Item 4.	Purpose of Transaction
	Item 4 of the Schedule 13D is hereby amended and supplemented by the addition of the following: On November 10, 2026, in light of the pending expiration of an existing antitrust clearance, the Reporting Person filed for early termination under the Hart-Scott-Rodino Antitrust Improvements Act of 1976. This filing is not related to any disagreement or dispute with the Issuer, its management, or the Board on any matter relating to the Issuer's operations, policies, or practices.
Item 5.	Interest in Securities of the Issuer
(a)	Item 5(a) is hereby amended and restated in its entirety as follows: See rows (11) and (13) of the cover page to this Schedule 13D for the aggregate number of Shares and percentage of Shares beneficially owned by the Reporting Person. The percentage of Shares reported to be beneficially owned by the Reporting Person is based upon 60,863,586 Shares outstanding as of September 1, 2026, as reported in the Issuer's proxy statement on Schedule 14A, filed with the SEC on September 17, 2026. As of the date hereof, JANA may be deemed to beneficially own 3,880,671 Shares, representing approximately 6.4% of the Shares outstanding. This includes 9,542 deferred stock units ("DSUs") granted to Mr. Ostfeld for his service on the Board, 7,194 of which have vested and 2,348 of which were granted on October 28, 2026 and will vest on the earlier of the first anniversary of the grant date and the next annual meeting of shareholders. Vested DSUs do not convert into Shares until the date on which Mr. Ostfeld ceases to be a member of the Board. Mr. Ostfeld has assigned all rights to any Shares issuable pursuant to the grant to the Reporting Person. Pursuant to the assignment, settlement of the award on vesting will be made to the Reporting Person.
(b)	Item 5(b) is hereby amended and restated in its entirety as follows: See rows (7) through (10) of the cover page to this Schedule 13D for the number of Shares as to which the Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition.
(c)	Item 5(c) is hereby amended and restated in its entirety as follows: No transactions in the Shares have been effected by the Reporting Person during the past sixty (60) days.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

JANA Partners Management, LP

Signature:	/s/ Jennifer Fanjiang
Name/Title:	Jennifer Fanjiang, Partner, Chief Legal Officer and Chief Compliance Officer
Date:	11/10/2026