Mark 13 torpedo

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.

At the close of the war, the Mark 13 was considered one of the most reliable air-dropped torpedoes available, "universally accepted as the best aircraft torpedo owned by any nation." They were also used on PT boats.

Design
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&mdash;even when dropped low to the water at slow speeds&mdash;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 2400 ft, at speeds up to 410 knots. The final Mark 13 weighed 2216 lb; 600 lb of this was the high explosive Torpex.

The Mark 13 was designed with unusually squat dimensions for its type: diameter was 22.4 in and length 13 ft. In the water, the Mark 13 could reach a speed of 33.5 kn for up to 6300 yards. The Mark 13 ran 12.8 kn slower than the Mark 14 torpedo. 17,000 were produced during the war.

The Mark 13 was very similar in design to the Mark 14 and Mark 15 torpedoes which suffered from problems such as submerged running approximately ten feet lower than set, contact exploder duds and magnetic trigger premature explosions. The Mark 13 design avoided these problems with its larger diameter, lesser mass, lesser negative buoyancy, slower running speed and the lack of a magnetic influence feature in its Mark IV exploder.