JANA reports 6.9% stake in Mercury Systems

JANA Partners Management filed Amendment No. 4 to its Schedule 13D on Mercury Systems Inc., updating its ownership disclosure.

Rhea-AI Filing Summary

JANA Partners Management filed Amendment No. 4 to its Schedule 13D on Mercury Systems Inc., updating its ownership disclosure. Based on 60,014,632 common shares outstanding as of January 31, 2026, JANA reports beneficial ownership of 4,114,618 shares, or about 6.9% of the company.

The position includes deferred stock units granted to Board member Mr. Ostfeld: 4,832 DSUs from October 23, 2024 and 2,362 DSUs from October 22, 2025. These DSUs vest on the earlier of one year after grant or the next annual shareholder meeting and convert into shares when he leaves the Board, with all rights to the underlying shares assigned to JANA. JANA has sole voting and dispositive power over the reported shares, exercised by its principal, and recent transactions were executed in the open market through brokerage firms.

FAQ

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

What stake does JANA Partners report in Mercury Systems (MRCY)?

JANA Partners reports beneficial ownership of 4,114,618 Mercury Systems shares, representing about 6.9% of the outstanding common stock. This percentage is based on 60,014,632 shares outstanding as of January 31, 2026, as disclosed in Mercury’s latest quarterly report.

How is JANA Partners’ ownership percentage in MRCY calculated?

The 6.9% ownership is calculated using 4,114,618 shares JANA may be deemed to beneficially own divided by 60,014,632 Mercury Systems shares outstanding. The outstanding share count comes from Mercury’s Form 10-Q for the quarter ended December 26, 2025, filed February 3, 2026.

What role do deferred stock units play in JANA’s MRCY stake?

JANA’s stake includes deferred stock units granted to Board member Mr. Ostfeld: 4,832 DSUs from October 23, 2024 and 2,362 DSUs from October 22, 2025. These awards ultimately settle in shares assigned to JANA when Mr. Ostfeld ceases serving on the Board.

When do the Mercury Systems deferred stock units granted to Mr. Ostfeld vest?

The deferred stock units vest on the earlier of the first anniversary of each grant date and the next annual meeting of shareholders. After vesting, they do not convert into Mercury Systems shares until the date when Mr. Ostfeld is no longer a Board member.

Who has voting and dispositive power over JANA’s Mercury Systems shares?

JANA Partners has sole voting and sole dispositive power over 4,114,618 Mercury Systems shares. This authority is exercised by its principal, meaning JANA alone decides how these shares are voted and whether, when, and how they are sold.

How were JANA’s recent Mercury Systems share transactions executed?

Transactions in Mercury Systems shares during the past sixty days were executed in the open market through various brokerage entities. Specific trade details are listed in Schedule A of the filing, which is incorporated by reference into the updated ownership disclosure.

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

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Accepted by SEC EDGAR 03/04/2026 - 09:46 PM EST Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)

MERCURY SYSTEMS INC

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

Ele Klein & Adriana Schwartz
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)

03/03/2026

(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).

SCHEDULE 13D

CUSIP Number(s):

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 4,114,618.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 4,114,618.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

4,114,618.00

12

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

13

Percent of class represented by amount in Row (11)

6.9 %

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. 4 ("Amendment No. 4") 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. 4 amends Item 5 as set forth below. Capitalized terms used herein and not otherwise defined in this Amendment No. 4 have the meanings set forth in the Schedule 13D.
Item 5.	Interest in Securities of the Issuer
(a)	Item 5(a) of the Schedule 13D is hereby amended and restated in its entirety as follows: The aggregate percentage of Shares reported to be beneficially owned by the Reporting Person is based upon 60,014,632 Shares outstanding as of January 31, 2026, as reported in the Issuer's Quarterly Report on Form 10-Q for the quarterly period ended December 26, 2025, filed with the SEC on February 3, 2026. As of the close of business on the date hereof, JANA may be deemed to beneficially own 4,114,618 Shares, representing approximately 6.9% of the Shares outstanding. This includes 4,832 deferred stock units ("DSUs") granted to Mr. Ostfeld on October 23, 2024 and 2,362 DSUs granted to Mr. Ostfeld on October 22, 2025, for his service on the Board of Directors of the Issuer (the "Board"). The DSUs 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) of the Schedule 13D is hereby amended and restated in its entirety as follows: The Reporting Person has sole voting and dispositive power over 4,114,618 Shares, which power is exercised by the Principal.
(c)	Item 5(c) of the Schedule 13D is hereby amended and restated in its entirety as follows: Information concerning transactions in the Shares effected by the Reporting Person in the past sixty (60) days is set forth in Schedule A hereto and is incorporated herein by reference. All of the transactions in Shares listed therein were effected in the open market through various brokerage entities.

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:	03/04/2026