Mark 13 torpedo

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Mark 13 torpedo
Mark13-torpedo-on-Wasp.jpg
A Mark 13B torpedo being loaded onto a TBF Avenger aboard the Wasp in 1944; the torpedo is fitted with wooden breakaway nose and tail protection which is shed upon hitting the water
Type Aerial torpedo
Place of origin United States
Service history
In service 1936–1950[1]
Used by United States Navy
Wars World War II
Production history
Designer Bureau of Ordnance[2]
Bureau of Aeronautics
Designed 1925[2]
Manufacturer Naval Torpedo Station[1]
Pontiac Motor Division
Amertorp Corporation
International Harvester
Produced 1942-1945[2]
Number built 16,600[2]
Variants Mod 1[3]
Mod 2[3]
Mod 2A - Mod 13[4]
Specifications
Weight 2216 pounds[1]
Length 161 inches[1]
Diameter 22.5 inches[1]

Effective firing range 6300 yards[1]
Warhead Torpex[1]
Warhead weight 600 pounds[1]
Detonation
mechanism
Mk 8, contact[1]

Engine Turbine[1]
Speed 33.5 knots[1]
Guidance
system
gyroscope[1]
Launch
platform
Douglas TBD Devastator[2]
Grumman TBF Avenger

The Mark 13 torpedo was the U.S. Navy's most common aerial torpedo of World War II. It was the first American torpedo to be originally designed for launching from aircraft only.[3] They were also used on PT boats.

Design[edit]

Mark 13 torpedo's general arrangement, as published in a service manual
Douglas TBD Devastator making a practice drop with a Mark 13 torpedo, October 20, 1941

Originating in a 1925 design study, the Mark 13 was subject to changing USN requirements through its early years with resulting on-and-off development. Early models—even when dropped low to the water at slow speeds—were prone to running on the surface, or not running at all. By late 1944, the design had been modified to allow reliable drops from as high as 2,400 ft (730 m), at speeds up to 410 knots (760 km/h). The final Mark 13 weighed 2,216 lb (1,005 kg); 600 lb (270 kg) of this was the high explosive Torpex.[1]

The Mark 13 was designed with unusually squat dimensions for its type: diameter was 22.5 inches (570 mm) and length 13 feet 5 inches (4.09 m). In the water, the Mark 13 could reach a speed of 33.5 knots (62.0 km/h; 38.6 mph) for up to 6,300 yards (5,800 m).[2][3] The Mark 13 ran 12.8 knots (23.7 km/h; 14.7 mph) slower than the Mark 14 torpedo. 17,000 were produced during the war.[4]

Wartime development[edit]

The following quote gives a brief overview of wartime Mark 13 development:

Despite the complications that were attending the other phases of torpedo development, the Bureau of Ordnance considered the aircraft torpedo problem so important that it was assigned the highest priority at the Newport Station. The improvements and modifications of 1942 and 1943 still left the weapon unpopular, however, and production problems were as great as those stemming from incomplete development. In mid-1943 an analysis of 105 torpedoes dropped at speeds in excess of 150 knots showed clearly why aviators distrusted the Mark 13: 36 percent ran cold, 20 percent sank, 20 percent had poor deflection performance, 18 percent gave unsatisfactory depth performance, 2 percent ran on the surface, and only 31 percent gave a satisfactory run. The total in excess of 100 percent proved that many torpedoes were subject to more than one of the defects, just as the bulk of the problems were still due to the effects of poor air stabilization on water behavior. Better performance at reduced aircraft speeds was small comfort since aviators could not be held down by paper restrictions that imposed serious and dangerous handicaps in combat. And even when they accepted the limitations, the water entry behavior of the torpedo produced frequent hooking and broaching. Time promised to complicate the problem still further. Unsatisfactory for existing planes, the torpedo would certainly fail to utilize the potentialities of aircraft then under development.

Confronted with such a problem, the Bureau felt that it had two alternatives: it could accept the Mark 13 as an interim weapon with recognized tactical limitations and initiate the design of a new torpedo, or it could concentrate on eliminating the known defects in the existing weapon. To attempt both might spread effort too thin to assure success in either venture. The first alternative involved predictable delay, since the Bureau estimated that 2 years would be required to move a weapon from conception to production. On the other hand, 12 known defects seemed to preclude immediate success in converting the Mark 13 into an effective aircraft torpedo. Neither alternative was considered alone, so the Bureau decided to increase its resources and follow both at once. The National Defense Research Committee was appealed to for aid, and in late 1942 it accepted a double-barreled order from the Bureau. The Committee was given a blank check to produce a new aircraft torpedo, the Mark 25, for tactical use at 350 knots launching speed, and it agreed to aid the Bureau in making immediate improvements to the Mark 13.

New planes outdated Torpedo Mark 13, but drag rings and stabilizers renewed its usefulness. Throughout 1943 torpedo performance remained poor,but the following year witnessed a revolution in the behavior of the Mark 13. Minor changes to the propeller blades and a reduction in gyro damage helped, but the greatest improvement resulted from the stabilizing effects of two appendages--the drag ring and the shroud ring. The first assembly, known familiarly as the pickle barrel, was readied for use by 1944. Early experiments with parachutes attached to aircraft torpedoes had demonstrated that a drag had a beneficial effect on the airflight characteristics of the weapon. While parachutes did not appear the solution to the problem, discovery of the principle involved led to the development of the drag ring. Constructed of plywood, the ring was attached to the head of a torpedo and served as a stabilizer for the period that the weapon was airborne. Oscillations were reduced and the ring effected a 40 percent deceleration in air speed, then acted as a shock absorber when the torpedo struck water. Better water entry, a byproduct of air stabilization, reduced damage so substantially that pilots were able to increase the heights and speeds at which torpedoes were released.

The drag ring went a long way toward making the Mark 13 a reliable torpedo, but underwater performance still called for improvement. By midsummer 1944, however, the shroud ring developed by the California Institute of Technology completed the torpedo revolution that had seemed so remote the year before. Almost an exact duplicate of an assembly developed by Newport in 1871, the shroud ring was made to fit over the tail blades of the torpedo. Known to pilots as the ring tail, it produced a steady water run by reducing hooks and broaches and eliminating much of the water roll which characterized the Mark 13. Speed and range were reduced but slightly. Early tests showed that ring-tailed torpedoes took too deep an initial dive, but readjustments of controls soon remedied that last obstacle. Hot, straight, and normal runs approached 100 percent, and the once critical battle reports soon became enthusiastic in praise of the Mark 13. Even psychologically, the appendages contributed to success,since the external design of the torpedo equipped with a pickle barrel and ring tail and the improved appearance of its underwater travel caught the fancy of the airmen.

To speed the availability of the modified torpedo the Bureau built tail assemblies with the shroud ring attached, then sent them to the fleet as substitutes for the equipment on hand. By the fall of 1944 the revamped weapon had a wide distribution. As a result of the new improvements, torpedo drops at altitudes up to 800 feet and at speeds up to 300 knots were authorized. Experience soon indicated that these limits could be extended even further. On one occasion in early 1945, 6 Mark 13 torpedoes were released from altitudes between 5000 and 7000 feet; 5 out of the 6 were observed to run hot, straight, and normal. Combat use increased rapidly and the new effectiveness seemed out of all proportion to the changes made. On one air strike on April 7, 1945. Mark 13's sent to the bottom the 45,000 ton battleship Yamato, a light cruiser, and several destroyers. Months before the end of the war the Mark 13 was universally accepted as the best aircraft torpedo owned by any nation.[5]

See also[edit]

References[edit]

  1. ^ a b c d e f g h i j k l "Torpedo History: Torpedo Mk 13". Retrieved 2013-06-05. 
  2. ^ a b c d e Jolie, E.W. (15 September 1978). "A Brief History of U.S. Navy Torpedo Development". Retrieved 2014-10-29. 
  3. ^ a b c Torpedo Mark 13, OP 629(A), Description, Adjustment, Care, and Operation. United States Navy. July 1942. 
  4. ^ "United States of America Torpedoes Pre-World War II". Retrieved 24 June 2013. 
  5. ^ Rowland, Buford. "U.S. Navy Bureau of Ordnance in World War II". Retrieved 2013-06-05. 

Notes[edit]

  1. ^ National Museum of the United States Air Force. Mark 13 Torpedo". Archived on July 9, 2006.
  2. ^ NavWeaps (18 February 2005). "USA Torpedoes of WWII". Retrieved 2 August 2005.
  3. ^ Milford, Frederick J. U. S. Navy Torpedoes; Part One: The great torpedo scandal, 1941–43. The Submarine Review, April 1996. Archived on October 14, 2007.
  4. ^ Milford, Frederick J. U. S. Navy Torpedoes; Part Two: The great torpedo scandal, 1941–43. The Submarine Review, October 1996. Archived on December 10, 2005.

External links[edit]