The Type 93 (酸素魚雷, designated for Imperial Japanese calendar year 2593) was a 610 mm (24 in)-diameter torpedo of the Imperial Japanese Navy (IJN), launched from surface ships. It is commonly referred to as the Long Lance by most modern English-language naval historians, a nickname given to it after the war by Samuel Eliot Morison, the chief historian of the U.S. Navy, who spent much of the war in the Pacific Theater. In Japanese references, the term Sanso gyorai (酸素魚雷, lit. "oxygen torpedo") is also used, in reference to its propulsion system. It was the most advanced naval torpedo in the world at the time.