 Unreliable torpedoes caused many problems for the American submarine force in the early years of the war, primarily in the Pacific Theater.One possible exception to the pre-war neglect of torpedo development was the 45-cm calibre, 1931-premiered Japanese Type 91 torpedo, the sole aerial torpedo ("Koku Gyorai") developed and brought into service by the Japanese Empire before the war.The Type 91 had an advanced PID controller and jettisonable, wooden "Kyoban" aerial stabilizing surfaces which released upon entering the water, making it a formidable anti-ship weapon; Nazi Germany considered manufacturing it as the "Luftorpedo LT 850" after August 1942..