Chrysler tank arsenal. This is a milling operation. The four-pound metal piece with the aperture is actually the turret for a 37 mm anti-aircraft gun, part of the equipment for an M-3 tank. Extreme accuracy is required in the milling of these parts, because it is important that they be able to move freely. The gun is designed for straight away shooting, as well as serial shooting. The twenty-eight ton M-3 tanks are made in Detroit, at the huge Chrysler tank arsenal