GAU-21

Also known as

FN M3M
M3M
FN M3M (GAU-21)
Gun, Aircraft, Unit-21

The GAU-21 is FN Herstal's U.S. Navy designation for the M3M .50-caliber machine gun, a remote-fired rotary-wing gun for helicopter and aircraft mounts. FN says the design is an evolution of the M3 family, and DVIDS documents HH-60W testing with the weapon in 2022.

GAU-21, .50-caliber machine gun, Infantry Weapons

Image source: FN® M3M (GAU-21) | FN® Firearms

Profile / Specs

Profile

Origin: Belgium
Built by: FN Herstal
Type: .50-caliber machine gun
Service note: 2004-present
Designer: FN Herstal
Unit cost: Military pricing on request
Produced: 2004-present

Specifications

Caliber: 12.7x99 mm NATO / .50 BMG
Operation: Short-recoil, open-bolt
Rate of fire: 950-1,100 rounds per minute
Weight: 81.6 lb
Barrel length: 36 in
Effective range: Nearly 2,000 m
Capacity: 100-600 rounds
Mounting: Rotary-wing aircraft, other U.S. service mounts, and naval applications

Firing Platforms

DVIDS documented the GAU-21 on the HH-60W Jolly Green II during Air Force testing in 2022.

Firing weapon	Weapon type	Firing evidence
HH-60W Jolly Green II	Combat rescue helicopter	DVIDS says the 41st Rescue Squadron was the first in the U.S. Air Force to test the GAU-21 .50 caliber machine gun on the HH-60W Jolly Green II in March 2022. Sources: 41 RQS tests GAU-2C, GAU-21 weapon systems

Firing weapon

Weapon type

Firing evidence

HH-60W Jolly Green II

Combat rescue helicopter

DVIDS says the 41st Rescue Squadron was the first in the U.S. Air Force to test the GAU-21 .50 caliber machine gun on the HH-60W Jolly Green II in March 2022.

Sources: 41 RQS tests GAU-2C, GAU-21 weapon systems

Designation And Mounting

FN's product page identifies the GAU-21 as the U.S. Navy designation for the M3M and places it on rotary-wing aircraft mounts across U.S. service branches.

Designation	Weapon detail	Reader note
GAU-21	U.S. Navy designation for the FN M3M	FN says the designation was adopted in 2004.
Platform use	Rotary-wing aircraft mounts	FN says the gun is in operation on multiple rotary-wing platforms across the U.S. Navy, Marine Corps, and Air Force.
Operating method	Open-bolt, dual-recoil-buffer design	FN describes the gun as producing 1,100 rounds per minute through open-bolt operation and a dual recoil buffer system.

Service And Conflict Use

Service History

In service: U.S. Navy-designated GAU-21 service on rotary-wing aircraft and other U.S. service mounts since 2004.
Used by: United States Navy, United States Marine Corps, United States Air Force

Media