Common Stock, par value $0.01 per share

MERCURY SYSTEMS INC

50 MINUTEMAN ROAD, ANDOVER, MA, 01810

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.

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.

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.