With no evidence or aerodynamic analysis, the Navy guessed that the big tail fins had been the key to the Japanese torpedo attack. These were again made of metal covered with wooden gloves that snapped off at water entry. The Navy also saw that there were two smaller fins near the front of the tail cones. These big wooden fins, which were fitted over smaller metal fins, broke off when the torpedo hit the water. They saw that the dropped torpedoes had big wooden fins at the back of their tail cones. Navy examined the remnants of Japanese torpedoes. 7, 1941, Japan proved that it had mastered shallow-water torpedo strikes. However, what this meant for Pearl Harbor, which was much shallower, was not clear.ДЇigure 1 : Water strike by a British aerial torpedo (aircraft is a Fairley Swordfish)ДЄ 1,600-lb. Kimmel warning that, contrary to previously sent information, successful attacks could take place in harbors less than 75 feet deep. A year earlier, the British had attacked Italian ships in Taranto Harbor, which was 60 to 75 feet deep where the British torpedoes launched. Pearl Harbor was only about 40 feet deep, so Japan needed to modify its tactics and torpedoes to attack successfully. In the open sea, JapanвЂ™s aerial torpedoes plunged 150 feet before climbing back to attack depth. When an aerial torpedo weighing almost two tons slams into the water at 200 mph, it barely slows down. Playing out from a drum attached to the airplane, the wire exerted upward resistance on the nose, keeping it from rotating downward too steeply. They attached a wire to the torpedoвЂ™s nose.

The British used an entirely different system for their shallow-water attack at Taranto Harbor a year earlier.It allowed the aircraft to drop their torpedoes from an altitude of 66 feet (20 m) and at a speed of 185 mph (160 kt, 300 km/h).This would not be possible if the torpedo were rolled when it hit the water. This allowed the torpedoвЂ™s horizontal rudders to be used to pitch the nose up immediately on impact with the water.They ensured that the torpedo dropped without roll. These were gyroscopically driven ailerons.The enabling innovation was small wooden fins near the front of the tail cone.The big stabilizing fins at the rear of the tail cone were an older modification unrelated to this problem.They needed to limit the initial plunge so that the torpedoes would not strike the bottom mud.The Japanese had to modify their Type 91 Modification 2 aerial torpedoes for the Pearl Harbor attack.By Ray Panko | | Pearl Harbor Aviation Museum JapanвЂ™s Type 91 Modification 2 Torpedo Fins at Pearl Harbor

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