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Type 91 Model 2
||17.7" by 18'0"
45cm by 5.486m
|Range||2200 yards (2000m) at 42 knots
|Warhead||452 lbs Type 97 explosive
205 kg Type 97 explosive
|Propulsion||Kerosene-air two-row eight-cylinder radial wet heater (210 bhp) driving contra-rotating four-blade propellers
The Model 1, produced up to April 1941, was
slightly shorter and had only a 331 lb (150 kg) charge.
The Model 3, produced after October 1941,
increased the charge to 529 lbs (240 kg).
The Model 3 Improved, produced from 1943,
could be launched at 300 knots.
The Model 3 Strong, introduced in 1944,
sacrificed range (1640 yards or 1500m at 42 knots) for a launch speed
of 350 knots.
The Model 4 Strong, introduced later in
1944, increased the charge to 538 lbs (244 kg).
The Model 7 Strong, introduced in late
1944, increased the charge to 926 lb (420 kg) at the cost of a knot in
The Type 91 was the principal aircraft torpedo of the Japanese Navy. Unlike most other Japanese torpedoes, it did not use pure oxygen. Although the Japanese had experimented with a pure oxygen aircraft torpedo (Type 94) the complications and hazards involved were eventually judged not worth the increase in performance.
This torpedo was nonetheless a good weapon, reliable
and with a high maximum launch speed. However, contrary to Japanese
expectations, a single hit was not capable of penetrating the torpedo protection of American battleships. In the attack on Pearl Harbor, Nevada was hit by a single Type 91 Mod 2 that split seams and caused leaks, but did not penetrate the holding bulkhead. California was hit by two Type 91 Mod 2 torpedoes that deflected the holding bulkhead inwards but left it intact. California sank only because the hatches to the void spaces of the underwater protection system
had been left open for an upcoming inspection, allowing extensive
flooding that would not have taken place had the ship beenin watertight condition.
The warhead was fitted with a 0.4" (1 cm) protective rubber sheath which shattered on impact with the water. The Japanese believed this to be superior to the wooden nose shroud used on American Mark 13 torpedoes. However, the Japanese did use plywood tail appendages to help stabilize the torpedo after it was dropped. These broke away on impact with the water. The earliest models of the Type 91 were stabilized against rolling by leaving the warhead only partially filled, and much of the increase in explosive charge in later models came from improved anti-roll flippers that allowed the warhead to be completely filled.
When dropped from low altitude at very high speed, the
Type 91 sometimes buckled around the engine chamber. The Strong models
corrected this problem and permitted a greater launch speed.
Branfill-Cook (2014) describes a Type 4 torpedo, which may be identical
from the Type 91 Mod 4 Strong, which could be launched at up to 400
The Japanese experimented with a shaped charge
warhead, the "V" warhead, for the Type 91. Tests demonstrated that this
could punch completely through the underwater protection of a Colorado-class battleship. However, only three saw use in combat.
The Japanese also developed and began deploying an antisubmarine
variant of the Type 91, the QR, that was set to circle and descend after
being dropped. The diameter of the circle was 300 yards (290m) and the
maximum depth was 320' (100m). Only fifty were produced and there is no
record of operational use.
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