That is the Quad 50 Calibre Machine Gun. Actually it's four of John Brownings finest machine guns (M2, aka "Ma Duce") mounted and operated in one frame. The M2 was originally used during WW2 as an aircraft weapon on planes such as the P47, and the P51 Mustang.
As you see, it is not a small round. The bullet is a half-inch round and two inches long. The casing is three-quarters inch round and four inches long. It's a powerful round. PS: that's a souveigner casing without powder, note the holes drilled in the side of it.
There were four Quads at French Fort, one on each corner of the compound. There was a gun crew assigned to each unit. The effective range was about 1.2 miles. They were very impressive for perimeter defense.
There was a can of ammo feeding each gun, a crew man on each side of the gun fed the ammo. It could shoot at 600- 1,200 rounds per minute. It did not sustain that rate very long as the barrels would get red hot and start to sag.
The upright plates you see were there to protect the ammo man. He was a prized target for the enemy because without him the gun would stop firing. This four barrel configuration was originally devised as an anti-aircraft gun, but it worked fine for perimeter defense.
The gun turrent swivelled up and down and turned left and right for a complete field of fire. It was all done with electric motors. The gunner had a steering wheel sort of like an aircraft wheel, with thumb triggers in it.
The gunner is in the cockput, and the ammo man is finishing loading.
The yellow spots in the center of the photo are tracer rounds. On belt ammo every fifth round was a tracer. Helped you see what your were hitting during night fire.
