Japan’s Type 91 Modification 2 Torpedo Fins
- The Japanese had to modify their Type 91 Modification 2 aerial torpedoes for the Pearl Harbor attack.
- They needed to limit the initial plunge so that the torpedoes would not strike the bottom mud.
- The big stabilizing fins at the rear of the tail cone were an older modification unrelated to this problem.
- The enabling innovation was small wooden fins near the front of the tail cone
- These were gyroscopically driven ailerons. They ensured that the torpedo dropped without roll.
- This allowed the torpedo’s horizontal rudders to be used to pitch the nose up immediately on impact with the water. This would not be possible if the torpedo were rolled when it hit the water.
- This reduced the initial plunge.
- 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).