[Llarry]

The current lightweight (500-800 pounds) ASW torpedoes are greatly improved over the old WW2 FIDO. The FIDO had a max speed of 12 knots for 10 minutes; this in an era when the underwater speed of a submarine was typically less than 10 knots. Modern submarines have underwater speeds of 20 knots or more, with the nukes doing 30+ knots. A homing torpedo had better have a good turn of speed.

The USN currently uses three different lightweight ASW torpedoes -- all have a diameter of 12.75 inches (324 mm): The oldest is the Mark 46. The Mark 46 became operational in the early 1960s and in the U.S. Navy is fired from triple torpedo tubes on surface combatants and air-dropped by parachute from helicopters or patrol planes. It is credited with a speed of 40 or more knots and has a range of 11 km.

The Mark 46 was not up to the task of killing the most advanced Soviet submarines of the Cold War and the Mark 50 was to be its replacement. Developed in the '90s, the Mark 50 torpedo had good performance and was deeper diving but was deemed too expensive to be bought in quantity. It is in the fleet but in smaller numbers.

The Mark 54 is a hybrid of the Mark 50 guidance section with the propulsion system of the older Mark 46 and is in wide use, replacing the Mark 46.

These U.S. torpedoes are also used by many allies. There are also similar torpedoes produced by the UK (Sting Ray) and France and Italy (Mu90).

The latest innovation in ASW torpedo delivery is the dropping of a torpedo from a Boeing P-8A from higher altitude as a winged glider.