The two were built for the Imperial Japanese Navy (IJN) during World War II. Both ships of the class, and , were originally laid down as luxury passenger liners before being acquired by the IJN for conversion to aircraft carriers in 1941. Jun'yō was the first of the sister ships to be completed in May 1942 and the ship participated in the invasion of the Aleutian Islands the following month. Both ships participated in several battles during the Guadalcanal Campaign in late 1942. Their aircraft were disembarked several times and used from land bases in a number of battles in the South West Pacific. Hiyō was torpedoed in June 1943 and Jun'yō in November; both ships spent about three months under repair. They spent most of the time after their repairs training and ferrying aircraft before returning to combat. Hiyō was sunk by a gasoline vapor explosion caused by an American aerial torpedo hit during the Battle of the Philippine Sea in mid-1944 while Jun'yō was damaged by several bombs. Lacking aircraft, she was used as a transport in late 1944 and was torpedoed in December. The ship was under repair until March 1945 when the repairs were deemed uneconomical. Jun'yō was then effectively hulked for the rest of the war. After the surrender of Japan in September, the Americans deemed the ship not worth her repair costs; she was broken up in 1946–1947. Design and description The ships were ordered as the fast luxury passenger liners Izumo Maru and Kashiwara Maru by Nippon Yusen Kaisha (Japan Mail Steamship Company-NYK) in late 1938. In exchange for a 60% subsidy of their building costs by the Navy Ministry, they were designed to be converted to aircraft carriers. To facilitate this process, they were fitted with a double hull, additional fuel oil capacity, provisions for the fitting of additional transverse and longitudinal bulkheads, installation of a longitudinal bulkhead to separate the turbine rooms, a strengthened main deck, more height between decks, rearrangement of the superstructure and passenger accommodations to facilitate the installation of aircraft elevators and hangars, more space for additional wiring, installation of a bulbous bow and the addition of aviation gasoline storage tanks fore and aft of the machinery spaces. NYK was only interested in a maximum speed of to save fuel, but the Navy wanted a maximum speed of no less than so they compromised by limiting the performance