In the movie Pearl Harbor (and boy, did that ever make me root for the Japanese), Cuba Gooding’s character races on deck during the raid and begins firing an anti-aircraft gun at the Zeros. I noticed that there’s some kind of metal pipes that hoop over Gooding’s shoulders to apparently aid in steering the gun. In the movie Tora! Tora! Tora!, the same character as Gooding’s, fires an anti-aircraft gun at Zeros, but this time there’s one pipe and it hoops around his waist. What’s the hoop called, and which of the two guns are more historically accurate? If both of them were in use at that time, then what’s the difference between the two of them?
and here
I have seen both shoulder rests and hip rests used in WW2 pictures. Both aid in slewing the gun around, as it was unpowered and rather heavy. 
I can’t dig up a picture at the moment, but I associate the “hoop” with the .50 caliber machine gun which preceded the 20mm Oerlikon as the Navy’s short-range AA weapon. As silenus said, both devices served the same purpose: to provide leverage when it came time to maneuver the weapon (they also helped stabilize it).
Since my recollection is that the Oerlikon was just starting to be deployed at the time of Pearl Harbor, it’s almost certain that Tora! Tora! Tora! was more accurate. But you’re not surprised, are you?