bubblehead

(military slang, derogatory) A submariner.

Military slang — specifically US Navy inside humor — for a submariner: someone who serves aboard submarines. Surface sailors use it as a lighthearted dig at the sub service, playing on the image of someone living in an air bubble deep underwater, cut off from the real world. Submariners often wear the label with a mix of pride and irony, since the sub community's insularity is both a running joke and a genuine point of culture. It can also mean an airhead, but the military sense is the sharper one.

(slang) A member of a navy; a sailor; a fisherman.