さすが日本人のアイディアをパクっただけあって性能が良くなったな
「The idea of the shroud ring ironically came from the Imperial Japanese Navy. In order to get their Type 91 aerial torpedoes to enter at the proper angle, the IJN added a wood box-shaped tail design to shear off when the torpedo entered the water and ensure it fired at the correct depth. This modification was used to excellent effect during their attack on Pearl Harbor on December 7th, 1941, but the US Navy first observed it May 8th, 1942. On this date during the Battle of the Coral Sea, Captain Fredrick of the USS Lexington noticed the addition of the wooden shroud rings on Type 91 torpedoes from B5N “Kate” torpedo bombers. As the Mark 13’s planned replacement, the Mark 25 was still undergoing development, the Mark 13-6 was built as an interim solution to improve the aerial torpedoes of the US Navy. Further improvements to the design led to the later Mk. 13-6 Case. 」