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National Archives #80-G-284708.
Cropped by author.
||22.4" by 13'5"
56.9cm by 4.089m
|Range||6300 yards (5760m) at 33.5 knots
|Warhead||600 lbs Torpex
262 kg Torpex
|Propulsion||Alcohol-air two-stage impulse turbine|
||17,000 during the war
The Mark 13 was the standard aircraft torpedo throughout the war. It was developed in 1936 and entered service two years later. Compared with the aircraft torpedoes of other powers, such as the Japanese Type 91, the Mark 13 was short, fat, slow, and long-ranged. It was also initially highly unreliable, requiring a drop at 50 feet (15m) at 110 knots and still often malfunctioning. Its one bright spot was that the contact detonator was reasonably reliable at the relatively slow speed (33 knots) of the Mark 13.
According to Branfill-Cook (2014), Captain Frederick Sherman of Lexington observed that Japanese B5N Kates launched their Type 91 torpedoes at high speed, and that the torpedo on a Kate that had been shot down had a wooden
box around its rudder. This prompted the Americans to revise their
aerial torpedo design. Modifications to the air tails and the addition
of nose drag rings
allowed high speed drops from 1000 feet (300m) by February 1944 and
from 2400 feet (730m) and 410 knots by the end of the war. Pilots were
trained that the optimum drop was from 800' (240m) at 260 knots from a
distance of 1400 yards (1300m). This yielded a water entry angle of
about 28 degrees after a fall of 7 seconds over a horizontal distance of
1000 yards (900 m), plus an additional water run of 400 yards (370m).
The nose drag
ring slowed the fall of the torpedo, while the air tail prevented the
torpedo from oscillating as it fell, which could cause the torpedo to
hit the water at an unfavorable angle, damaging the torpedo or causing
it to roll and be thrown off course. The engine was started using
compressed air during the air drop, to avoid burning out the turbines,
and fuel was not fed to the combustion chamber until impact with the
water sheared a control wire. These modifications reduced the range to
4000 yards, which mattered little in typical tactical settings.
The Mark 13 began to replace the Mark
8 on PT boats in
early 1944. Since the Mark 13 could be launched by simply rolling it
over the side of the boat, the boats were able to replace their heavy
torpedo tubes with enhanced machine gun and cannon armament.
Wildenberg and Polmar (2010)
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