This is a TDU. Trash disposal unit from a Submarine. Rare item since most of these end up on the bottom of the ocean!
Disposing of trash, like many other activities that are relatively straightforward ashore, require special arrangements in a submarine. Trash is tightly compacted in a cylindrical steel mesh container. A 7-lb (3.2 kg) weight ensures that it sinks to the bottom of the sea. Since the end of the Cold War, submarines operate under stricter rules about when and where they can discharge trash overboard, and some materials, like plastics, can no longer be discharged at all. TDU operation can be relatively noisy. When a submarine is rigged for quiet running, trash can accumulate on board for days or even weeks, lest the sounds of disposal alert a potential foe.