United States of America
Information on Torpedoes
Updated 20 December 2010

Torpedo Nomenclature

The USN originally procured torpedoes by contracting with private manufacturers.  Each vendor was assigned their own Mark number series and was given a designation in metric or in metric and english dimensions specifying how large was the torpedo in both diameter and length and the manufacturing name.  For example, the first Bliss-manufactured torpedoes based upon the Whitehead torpedo patents were designated as the Whitehead 3.55m x 45cm Mark I.  The first Bliss-Leavitt torpedoes manufactured to their own design were designated as Bliss-Leavitt 5m x 21-inch Mark I.

In 1913, the practice of assigning a series of marks to each manufacturer was changed to a single series of marks covering all manufacturers and older torpedoes were redesignated.  Surviving 45 cm torpedoes were designated as Types A through C while the 21-inch torpedoes were designated as Mark I through Mark 4.  Details may be found in the Pre-World War II USA torpedo datapage.  From that time onwards, the Mark number alone, or in a few cases the Mark and Mod numbers, uniquely identifies each torpedo.

USA torpedoes since that time are simply designated with "Mark" followed by a Numeral and a "Mod" followed by a number representing the change made since the basic design.  For example, the Designation "Mark 12 Mod 2" means that the torpedo is the twelfth torpedo designed by the USN and that it has undergone two design revisions since the first model.

In 1922, all torpedoes prior to the Mark 7 were declared obsolete and removed from service.  As of that point, only the Mark 7 (17.7") and Marks 8, 9 and 10 (all 21") remained in service.

All USN 18 inch torpedoes are actually 17.7 inches (45.0 cm) in diameter.

During World War I production was at the Alexandria Torpedo Station at Alexandria, Virginia.  This station was closed shortly after the war ended.  Production prior to World War II was at the Naval Torpedo Station at Newport, Rhode Island.  Efforts to reopen the Alexandria Station prior to World War II were frustrated for political reasons for 11 years before it was finally reopened in July 1941.  In addition to these two, Bliss and the Pontiac Division of General Motors made torpedoes during World War II and Westinghouse developed the Mark 18 Electrical Torpedo.  After World War II, Honeywell and later General Dynamics were the primary manufacturers while General Electric made some of the acoustic ASW torpedoes.

Torpedo Engines
1885 to 1905

The first USN torpedo was the Howell which used a flywheel for power.  Although modestly successful, the Whitehead type using compressed air was adopted as it was suitable to improvements to increase range and warhead size.

World War I and World War II Torpedoes

Unlike other nations, the United States abandoned the Whitehead compressed air torpedoes in favor of turbine propulsion as early as November 1907.  Wet-heater propulsion systems were introduced to USN torpedoes during the 1920s and became the primary motive power for the next two decades.

For example, the Mark 13 airborne torpedo of the 1930s-1940s was an alcohol-fuelled freshwater wet-heater using a two-stage impulse type turbine with contra-rotating rotors, no stator and three nozzles.  More energetic fuel systems including ones using pure oxygen and hydrogen peroxide ("Navol") instead of air were tested in the 1930s but these developments were dropped due to technical difficulties.

Newport Station worked intermittently on electric torpedoes between the wars, but it was not until a captured German G7e was supplied by the British in 1941 that interest was aroused enough to place a development contract.  These torpedoes were very popular with the US Submarine force as they were essentially wakeless.  However, post-war analysis showed that Japanese merchantmen rarely noticed a wake and the rather slow speed of the Mark 18 resulted in the standard wet-heater torpedoes having a 17% better hit rate against merchant ships and 250% better against escort ships.

Experiments with Navol were revived during World War II with about 1,000 torpedoes being completed too late to see service.

Post war torpedoes have been mainly electrics and otto-fueled pistons.

Production during World War I

Between 01 January 1917 and 30 November 1918, a total of 5,910 Mark 7 and Mark 8 torpedoes were ordered with 1,982 being actually delivered during this time period.  However, the massive numbers of "flush-decker" destroyers completed during and after the war resulted in a total production of about 3,000 Mark 8 torpedoes.

Production during World War II

   Mark 13 (aircraft) - 17,000
   Mark 14 (submarine) - 13,000
   Mark 15 (surface) - 9,700
   Mark 16 (hydrogen peroxide) - 1,000
   Mark 18 (electric) - 9,600
   Mark 23 (a Mark 14 variant) - 9,600

The numbers above are rounded off and include all torpedoes produced during the 1930s.

Warhead Explosives
The earliest weapons used wet gun-cotton.  Just prior to World War I, this was replaced with TNT.  Torpex (TPX) was introduced in the Fall of 1942.  In the late 1940s Torpex was replaced by HBX, then H-6 in the 1960s and by PBX in the 1970s.

Approximately 1.9 lbs. (0.9 kg) of wet gun-cotton is equivalent to 1.0 lbs. (0.45 kg) of TNT.

Torpex is a mixture of 37-41% TNT, 41-45% RDX (cyclonite, cyclomethylene trinitramine) and 18% aluminum.  HBX and H-6 are also TNT based with additives to increase their explosive power or increase their stability.

Torpex is attractive because of the increased explosive energy and higher detonation velocity of RDX as compared to TNT and the prolongation of the pressure wave by the aluminum.  On a weight basis, Torpex is conservatively estimated to be about 50% more effective than TNT as an underwater explosive against ships.  However, Torpex is more sensitive than TNT and RDX is expensive and difficult to make safely.

Warhead Pistols
World War II Torpedoes

The failure of the US Magnetic Pistol and backup striker gear is well known.  Much of this was due to peacetime economies, but excessive secrecy and far too little communications between the Naval Torpedo Station and the Fleet were also to blame, as well as the reluctance of the Bureau of Ordnance to accept good evidence of defects.  The result was that it was not officially announced until August 1942 that the standard submarine torpedo Mark 14 ran 10 feet (3 m) below its depth setting and not until June 1943 that the magnetic pistol was ordered to be disabled.  However, long before this time, many submarine commanders were putting to sea per orders with activated pistols only to deactivate them once out of sight of land.  The contact exploder faults were finally rectified in September 1943 but magnetic exploders were distrusted as late as thirty years after the war ended.

The United States produced a total of 57,653 torpedoes between 1 January 1939 and 1 June 1946.  Newport built 18,751, Alexandria built 9,920, Westinghouse 8,250, Forest Park 8,391, St. Louis 6,257, Keyport 795, and Pontiac and International Harvester built 5,289.

Other information on US torpedoes may be found at the off-site links given on the previous page.

Data from
"Naval Weapons of World War Two" by John Campbell
"The Naval Institute Guide to World Naval Weapons 1991/92" and "US Naval Weapons" both by Norman Friedman
"U.S. Navy Bureau of Ordnance in World War II" by Lt. Cmdr. Buford Rowland, USNR, and Lt. William B. Boyd, USNR
"Ship Killers:  A History of the American Torpedo" by Thomas Wildenberg and Norman Polmar
Page History

05 November 2007 - Benchmark
20 December 2010 - Updated Nomenclature section