Mark 13 torpedo

Mark 13 torpedo
A Mark 13B torpedo being loaded onto a Grumman 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
Used by	United States Navy
Wars	World War II
Production history
Designer	Bureau of Ordnance Bureau of Aeronautics
Designed	1925
Manufacturer	Naval Torpedo Station Pontiac Motor Division Amertorp Corporation International Harvester
Produced	1942-1945
Number built	16,600
Variants	Mod 1 Mod 2 Mod 2A - Mod 13
Specifications
Weight	2216 pounds
Length	161 inches
Diameter	22.5 inches
Effective firing range	6300 yards
Warhead	Torpex
Warhead weight	600 pounds
Detonation mechanism	Mk 8, contact
Engine	Turbine
Speed	33.5 knots
Guidance system	gyroscope
Launch platform	Douglas TBD Devastator Grumman TBF Avenger Curtiss SB2C Helldiver Mark 1 Lightweight Rack

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. They were also used on PT boats.

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 (470 mph). The final Mark 13 weighed 2,216 lb (1,005 kg); 600 lb (270 kg) of this was the high explosive Torpex.

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). 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.

By 1942, poor combat performance had made it apparent that there were problems with the Mark 13, as 40 out of 44 torpedo bombers were lost at the Battle of Midway without scoring a single hit:

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.