Junyo, first of a class of two 24,100-ton aircraft carriers, was built at Nagasaki, Japan. She was begun as the civilian passenger liner Kashiwara Maru but was taken over by the Japanese Navy in 1940, while still on the shipways, and converted to a carrier. Completed in May 1942, early in June she participated in the attacks on U.S. Alaskan bases that accompanied the Battle of Midway. As one of four large aircraft carriers remaining after the Midway action, Junyo was an important unit of the Japanese fleet during the next two years, even though she had a lower speed (about 23 knots) and smaller air group (about fifty planes) than built-for-the-purpose fleet carriers.
In late October 1942, during the intense Guadalcanal Campaign, Junyo took part in the Battle of the Santa Cruz Islands. In that action, her planes attacked the U.S. carrier Enterprise, battleship South Dakota and light cruiser San Juan, scoring hits on the latter two. In mid-November, she played a covering role in the three-day-long Naval Battle of Guadalcanal. The following Spring, her planes were sent to Rabaul, with those of other Japanese carriers, for land-based attacks on the Allied forces gathering at Guadalcanal. In June 1943, Junyo helped protect a important convoy sent to reinforce the Japanese garrison on Kiska, in the Aleutian Islands.
A year later, as the U.S. assaulted the Mariana Islands, Junyo joined the rest of Japan's aircraft carriers in the sortie that produced Battle of the Philippine Sea on 19-20 June 1944. After that action, her air group was so depleted that she was unable to participate in the great Battle of Leyte Gulf in October. While operating off southern Japan on 9 December 1944, Junyo was badly damaged by torpedoes from the U.S. submarines Redfish (SS-395) and Sea Devil (SS-400). Since Japan's strategic situation was now so bad as to eliminate any need for a carrier fleet, she was not repaired for seagoing service. At the end of the Pacific War, Junyo was moored at Sasebo, where she was scrapped in 1947.
Hiyō was a Junyo-class aircraft carrier of the Imperial Japanese Navy. Begun as an ocean liner in 1939, she was purchased by the Navy Ministry in 1941 for conversion to an aircraft carrier. Completed shortly after the Battle of Midway in June 1942, she participated in the Guadalcanal Campaign in October and missed the Battle of the Santa Cruz Islands later that month because of an electrical generator fire. Her aircraft were disembarked several times and used from land bases in a number of battles in the South West Pacific. Hiyō was torpedoed in mid-1943 and spent three months under repair. She spent most of the next six months training and ferrying aircraft before returning to combat. She was sunk by a gasoline vapor explosion caused by an American torpedo hit during the Battle of the Philippine Sea in mid-1944.