Firing on the Move

The_Chieftain: Here. http://afvdb.50megs..../m1a1turret.jpg   If you look at the turret wall to the right of the gunner's position, you can see what almost looks like a backrest on the end of a long metal horizontal swing arm. This swings inward, to become parallel with the backrest, and essentially sandwiches the gunner in between the two of them. This holds him in place.