There have been a number of 21-inch torpedoes in service with the United States.
These have been used on ships and submarines of the U.S. Navy.
American 21-inch torpedoes are 533 millimeters (21 in) in diameter.
Ship classes that carried 21-inch torpedoes include: Mod.3: 801 lb (363 kg) TNT or 825 lb (374 kg) HBX Mod.0: 1,260 lb (570 kg) Torpex Mod.1 and 3: 746 lb (338 kg) Torpex or HBX (later used HBX-3) 960 lb (440 kg) Torpex (later used HBX) Mod.8: 1,260 lb (570 kg) HBX Mod.3:Range: 13,700 yd (12,500 m)Mod.8: same range as Mod.1 or Mod.3