Friday, April 12, 2019

Mark 45 ASTOR Torpedo Myth

Mark 45 ASTOR Torpedo Myth
Copyright 2019 by Michael H. Maggelet

  One pervasive myth about the Mark 45 ASTOR (Anti-Submarine Torpedo) is that it had a kill ratio of two- the target and the launching sub. This is not true, the Mk 45 was wire guided and command detonated, and the W34 nuclear warhead was not armed until the torpedo had travelled at least 2050 yards (6150 feet) at 40 knots. The Mk 45 had a maximum range of 12,000 yards.


  The fastest conventionally armed wire guided torpedo the US Navy had at the time was the Mark 37 Mod 2, which by 1968 had a speed of 17 or 26 knots, with a seeker range of 1000 yards, and max range of 23,500 yards at low speed. This was not adequate to catch and destroy fast moving surface vessels nor the new generation of Soviet nuclear submarines like the November class (introduced 1958). While the Mk 37 with its 330 pound HBX-3 warhead was suitable for killing snorkeling submarines, and disabling slow merchants and some warships, the Navy sought to improve their torpedoes with the development of the Mark 48 (development started in 1965, fielded in 1972). In the meantime, the Mark 45 ASTOR would have to suffice during a potential confrontation with a nuclear armed superpower such as the USSR.

  The approximate kill radius of the estimated 10 kiloton Mk 34 warhead was 2500 feet (833 yards) from the underwater burst point. This information is derived from data from several shots, most notably the 1962 deep water Operation Dominic “Swordfish” ASROC proof test, and the 1958 Operation Hardtack Wahoo shot. Although the Swordfish W44/ASROC test was a deep subsurface burst, shot data and damage to shallow depth “Squaw” target hulls showed some interesting data. There are many variables regarding distance, depth, refraction, and hull strength, but the following data is presented-


Hardtack I, Wahoo shot- 9 kt, 500 feet DOB (deep ocean)

Hardtack I, Umbrella shot- 9 kt, 150 foot DOB (on seafloor), Mk 7 test device.

Squaw 29, 1600’ (533 yards) from burst zero, slight damage.

SSK-3 Bonita, 2900’ (966 yds) from burst, no damage.

Swordfish shot, 9 kt, 641 feet DOB (in deep ocean), W44 proof test.

USS Razorback, 13,800 feet (4600 yds) from burst zero at periscope depth, no damage.

  As shown above, the USS Razorback (SS-394), a Balao class submarine, was 4600 yards from the burst point at periscope depth during the Swordfish shot. Shaking was felt within the sub, due to the cascading water falling back after the burst.

Thus, with a burst more than 4600 yards away from the launching submarine, an attack sub launching the Mk 45 ASTOR from periscope depth (and avoiding the ensuing radioactive base surge and foam patch) was safe from any damage or destruction.

ASROC Nuclear Weapons Effects Test (DOE Historical Films)

References- Info on the Mk 45 torpedo from DOE Historical Films; info on Mk 37 from congressional testimony; shot data from Defense Nuclear Agency. Torpedo data, unless otherwise noted, from "A Brief History of US Navy Torpedo Development" by E.W. Jolie, Weapons Systems Department, Naval Underwater Systems Center, 15 September 1978. Unclassified.


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