submarines. Germany disrupted the supply lines to Britain largely by use of submarine torpedoes, though submarines also extensively used guns. Britain and its allies also used torpedoes throughout the war. U-boats themselves were often targeted, twenty being sunk by torpedo. Two Royal Italian Navy torpedo boats scored a success against an Austrian-Hungarian squadron, sinking the battleship with two torpedoes. The Royal Navy had been experimenting with ways to further increase the range of torpedoes during World War 1 using pure oxygen instead of compressed air, this work ultimately leading to the development of the oxygen-enriched air 24.5 in. Mk. I intended originally for the s and battleships of 1921, both being cancelled due to the Washington Naval Treaty. Initially, the Imperial Japanese Navy purchased Whitehead or Schwartzkopf torpedoes but by 1917, like the Royal Navy, they were conducting experiments with pure oxygen instead of compressed air. Because of explosions they abandoned the experiments but resumed them in 1926 and by 1933 had a working torpedo. They also used conventional wet-heater torpedoes. World War II In the inter-war years, financial stringency caused nearly all navies to skimp on testing their torpedoes. Only the British and Japanese had fully tested torpedoes (in particular the Type 93, nicknamed Long Lance postwar by the US official historian Samuel E. Morison) at the start of World War II. 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 caliber, 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. The Royal Navy's 24.5-inch oxygen-enriched air torpedo saw service in the two battleships although by World War II the use of enriched oxygen had been discontinued due to safety concerns. In the final phase of the action against , fired a pair of 24.5-inch torpedoes from her port-side tube and claimed one hit. According to Ludovic Kennedy, "if true, [this is] the only instance in history of one battleship torpedoing another". The Royal Navy continued the development of