ventilating tube for submerged submarines, introduced in German U-boats during World War II. A basic problem of submarines powered by internal-combustion engines was that of recharging the batteries, which were used for propelling the boat when it was fully submerged. Because the generator (used for recharging the batteries) was powered by the internal-combustion engine, which required air, the submarine had to surface and so expose itself to detection if it wanted to recharge its batteries. The snorkel, raised while the submarine cruised just beneath the surface, permitted air intake and fume exhaust by the internal-combustion engine, so that the batteries could be recharged without the submarine having to surface.

Analogous tubes, also called snorkels, fitted to face masks permit swimmers to breathe while just below the surface of the water.