Marines with Marine Heavy Helicopter Squadron 462 conducted a GAU-21 weapons shoot from CH-53E Super Stallions.

 

https://youtu.be/mZ5s-VEmXGk

FN M3M (GAU-21)

The FN M3M (GAU-21) is a .50 caliber (12.7x99mm) single barrel rapid-fire machine gun suitable for rotary-wing aircraft applications providing defensive firepower ranging out to nearly 2000 meters.