Mercury Systems CEO granted 23,629 restricted stock units

Mercury Systems’ CEO reports an omitted three-year restricted stock unit grant and updated direct and indirect share holdings in an amended Form 4.

This filing corrects an earlier one, and you can read the original Form 4 if you want to see what changed.

Rhea-AI Filing Summary

MERCURY SYSTEMS INC (symbol: MRCY) is the issuer of record for a Form 4/A filing submitted to the SEC. Ballhaus William L reported acquisition or exercise transactions in this Form 4 filing.

MERCURY SYSTEMS INC (MRCY) reports that Chairman, President and CEO William L. Ballhaus received a grant of 23,629 shares of common stock in the form of restricted stock units on August 17, 2026, which this amended filing states had been inadvertently omitted from the original report.

The restricted stock units vest in equal annual installments over three years after the grant date. Following this grant, Ballhaus holds 324,782.325 shares of common stock directly, plus 1,403 shares through a retirement savings plan and 7,066.173 shares through Milestone Road Holdings, LLC, all as reported in this filing. No Rule 10b5‑1 trading plan is reported.

Insider Trade Summary

Grant/Award: 23,629 shares

Grant/Award 3 txns

Insider Ballhaus William L

Role Chairman, President & CEO

Type	Security	Shares	Price	Value
Grant/Award	Common Stock F1	23,629	$0.00	$0.00
holding	Common Stock	--	--	--
holding	Common Stock	--	--	--

Holdings After Transaction: Common Stock — 324,782.325 shares (Direct); Common Stock — 1,403 shares (Indirect, 401K Plan); Common Stock — 7,066.173 shares (Indirect, By Milestone Road Holdings, LLC)

Footnotes (1)

1. F1. Represents restricted stock units that vest in equal annual increments over the three-year period following the grant date.

Key Figures

Restricted stock units granted: 23,629 shares Direct common shares after grant: 324,782.325 shares Indirect shares via 401(k) plan: 1,403 shares +2 more

5 metrics

Restricted stock units granted 23,629 shares Grant to William L. Ballhaus on August 17, 2026

Direct common shares after grant 324,782.325 shares Direct holdings of William L. Ballhaus following the August 17, 2026 grant

Indirect shares via 401(k) plan 1,403 shares Indirect holdings for William L. Ballhaus through a retirement savings plan

Indirect shares via Milestone Road Holdings, LLC 7,066.173 shares Indirect holdings for William L. Ballhaus through Milestone Road Holdings, LLC

Transaction price per share $0.00 per share Grant of 23,629 restricted stock units on August 17, 2026

Key Terms

restricted stock units, vest, 401K Plan, indirect

4 terms

restricted stock units financial

"Represents restricted stock units that vest in equal annual increments over the three-year period following the grant date."

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

vest financial

"Represents restricted stock units that vest in equal annual increments over the three-year period following the grant date."

A vest is the process by which an employee earns the right to receive certain benefits or ownership interests, such as stock or retirement funds, over time. It’s similar to earning a reward gradually, ensuring that the benefit becomes fully yours only after a set period or meeting specific conditions. This makes it important for investors because it determines when they can actually claim or use those benefits.

401K Plan financial

"401K Plan"

A 401(k) plan is an employer-sponsored retirement savings account that lets workers set aside part of their paycheck into investments, often with tax breaks and sometimes with matching contributions from the employer. Think of it as a workplace piggy bank that grows through employee contributions, optional company top-ups, and market returns; it matters to investors because it shapes household retirement security, drives large flows of money into public markets, and affects a company’s compensation costs and ability to attract and keep talent.

indirect financial

"By Milestone Road Holdings, LLC"

FAQ

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

What insider transaction did MRCY disclose in this amended Form 4/A?

The company reports that its Chairman, President and CEO, William L. Ballhaus, received a grant of 23,629 restricted stock units of common stock on August 17, 2026, which had been inadvertently omitted from his prior ownership report.

How do the restricted stock units granted to the MRCY CEO vest?

The filing states that the 23,629 restricted stock units vest in equal annual increments over three years following the August 17, 2026 grant date.

What are William L. Ballhaus’s direct share holdings in MRCY after this grant?

After the grant, William L. Ballhaus is reported to hold 324,782.325 shares of Mercury Systems common stock directly.

What indirect MRCY share holdings are reported for the CEO?

The filing reports 1,403 shares held through a 401(k) plan and 7,066.173 shares held indirectly through Milestone Road Holdings, LLC for William L. Ballhaus.

Was a Rule 10b5-1 trading plan involved in this MRCY insider transaction?

No. The filing’s plan-status disclosure indicates no Rule 10b5-1 trading plan is reported in connection with this restricted stock unit grant.

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

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Available on EDGAR 09/15/2026 - 06:06 PM Accepted by SEC EDGAR 09/15/2026 - 06:06 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Ballhaus William L

(Last) (First) (Middle)

50 MINUTEMAN ROAD

(Street)

ANDOVER MASSACHUSETTS 01810

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
MERCURY SYSTEMS INC [ MRCY ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chairman, President & CEO

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
08/17/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)
08/18/2026

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	08/17/2026		A		23,629(1)	A	$0	324,782.325	D
Common Stock								1,403	I	401K Plan
Common Stock								7,066.173	I	By Milestone Road Holdings, LLC

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. Represents restricted stock units that vest in equal annual increments over the three-year period following the grant date.

Remarks:

This amendment is being filed to correct the inadvertent omission of the grant of restricted stock units to the reporting person on August 17, 2026.

	/s/ Douglas Munro, attorney-in-fact	09/15/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)