Mark 21 Mod 0 torpedo

The Mark 21 torpedo, designated Mark 21 Mod 0 was a passive acoustic homing torpedo designed in 1943 by Westinghouse Electric Corporation. The Mark 21 successfully passed launching tests in 1943, however, due to difficulties encountered by Westinghouse, the project was abandoned after a few development models had been built.

It used the widely-used Mark 13 torpedo as a basis, with the addition of passive acoustic homing. Propulsion was switched to electric, but weight restrictions limited the speed available.