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The Type 91 was an aerial torpedo of the Imperial Japanese Navy which was designed to be launched from an aircraft. It was used in naval battles in World War II. The Type 91 aerial torpedo had two unique characteristics: * Wooden attachments on the tail fins, that acted as aerodynamic stabilizers, which were shed upon water entry. * An angular acceleration control system (PID controller) to control rolling movements, which was very advanced for its time. This system made it possible to release the Type 91 not only at a cruising speed of 180 knots (or 333 km/h, 207 mile/h) at an altitude of 20 m (66 ft), but also in a power-glide torpedo-bombing run at the Nakajima B5N2 ''Kate'''s maximum speed of 204 knots (or 378 km/h, 234 mile/h). The Type 91 torpedo was 450 mm (17¾ in) diameter. There were five models put into service, with high explosive warheads weighing 213.5 kg to 526.0 kg (or 470.7 lb to 1160 lb) and having effective ranges of 1,500 m to 2,000 m (or 1,640 yd to 2,187 yd) at 42 knots (77.8 km/h or 48.34mph). Since the Type 91 torpedo was the only practical aerial torpedo of the Imperial Japanese Navy, it was simply known as the ''Koku Gyorai'', or aerial torpedo. Surface warships and submarines used other types of torpedo, namely the Type 93 and Type 95 respectively, while the Type 97 torpedo was designed for use by midget submarines. ==Thunder fish== The Thunder fish, type 91 torpedo (modification 2), was a shallow water aerial torpedo that was designed for and used in the attack on Pearl Harbor in 1941. Conventional torpedoes when launched from aircraft would dive to 100 ft before turning up to hit their targets. The waters of the lagoon at Pearl Harbor were much shallower so wooden fins were added to allow for shallow launching at low altitude. The name Thunder fish is a literal translation of the Japanese ''gyorai'', meaning "torpedo" (''gyo'' = fish, ''rai'' = thunder). The tactic was practised at a bay on Kyūshū island which resembled Pearl Harbor before being used in the attack in December 1941, launched from "Kate" B5N torpedo bombers.〔 The plan for attack was designed by naval air strategist Minoru Genda for Admiral Isoroku Yamamoto in the face of opposition from the majority Japanese navy view that victory could be achieved by the "The Great All-Out Battle" tactic of luring United States battleships into a major action at sea.〔 〕 The torpedo measured in length, with a diameter of , and weighed , with an explosive charge of . It had a range of and a speed of 42 knots. A slight variant was used to sink HMS Prince of Wales and HMS Repulse, launched from "Betty" G4M bombers in an action in the South China Sea three days after Pearl Harbor on December 10, 1941.〔 (【引用サイトリンク】title=Japan Torpedoes of World War II ) 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Type 91 torpedo」の詳細全文を読む スポンサード リンク
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