The two Hiyō-class aircraft carriers (飛鷹型航空母艦, Hiyō-gata kōkūbokan) were built for the Imperial Japanese Navy (IJN) during World War II.

Both ships of the class, Hiyō and Jun'yō, were originally laid down as luxury passenger liners before being acquired by the IJN for conversion to aircraft carriers in 1941.

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.

[3] Both ships were fitted with a pair of Mitsubishi-Curtis geared steam turbine sets with a total of 56,250 shaft horsepower (41,950 kW), each driving a 5.5-meter (18 ft) propeller.

[5] A large island was fitted on the starboard side that, for the first time in a Japanese carrier, was integrated with the ship's funnel.

As a result of the lessons learned from the Battle of Midway in June, the ships' fighter complement was strengthened to 21 Zeros, and the B5Ns were reduced to 9.

[9] The primary armament consisted of a dozen 40-caliber 12.7 cm Type 89 anti-aircraft (AA) guns in twin mounts on sponsons along the sides of the hull.

[11] The ships were also initially equipped with eight triple 25 mm Type 96 light AA guns alongside the flight deck.

The maximum effective rate of fire was only between 110 and 120 rounds per minute due to the frequent need to change the fifteen-round magazines.

[18] Upon arrival at Truk on 9 October, the two sisters were assigned to the Second Carrier Division to begin operations against American forces in the Guadalcanal area as part of the 3rd Fleet.

The next day, they found the small seaplane tender, McFarland, in Lunga Roads offloading avgas into barges.

The two carriers were intended to play a prominent role in the Japanese effort to retake Guadalcanal Island and were assigned to the Advance Force for this operation.

Their aircraft were supposed to provide air cover after the Japanese night attack that retook Henderson Field and then they were to be flown ashore,[20] but Hiyō's machinery problems caused her to return to Truk.

Her aircraft made hits on the carrier Hornet, the battleship South Dakota and the light cruiser San Juan, but inflicted little substantial damage.

[22] During this time, Hiyō's remaining aircraft flew to Rabaul on 23 October where they provided air cover for Japanese forces on Guadalcanal.

A detachment from the air group was transferred to Buin, Papua New Guinea on 1 November and participated in the Naval Battle of Guadalcanal later in the month.

Both ships returned to Truk in late March[19][21] and their air groups were detached from in early April to participate in Operation I-Go, a land-based aerial offensive against Allied bases in the Solomon Islands and New Guinea.

[21] Jun'yō's air group was deployed to Buin, Papua New Guinea on 2 July in response to the American invasion of Rendova Island on 30 June.

She arrived on 3 December and was almost immediately assigned duties as an aircraft ferry until January when the ship returned to Japan.

[29] The new base was closer to the oil wells in Borneo on which the Navy relied and also to the Palau and western Caroline Islands where the Japanese expected the next American attack.

However, the location lacked an airfield on which to train the green pilots and American submarines were very active in the vicinity which restricted the ships to the anchorage.

Upon reaching Guimaras, the fleet refuelled and sortied into the Philippine Sea where they spotted Task Force 58 on 18 June.

The three carriers launched multiple air strikes against the American ships, but generally failed to locate them and did not inflict any damage while losing most of their aircraft.

They discovered the retiring Japanese fleet during the afternoon of the following day and Vice Admiral Marc Mitscher ordered an air strike launched.

This knocked out the starboard engine room and started fires, but Hiyō was able to continue, albeit at a slower speed.

[33] After repairs at Kure, the ship remained in the Inland Sea without aircraft until 27 October when she was tasked to transport material to Borneo.

On 3 November, she was attacked by the submarine Pintado, but her escorting destroyer, Akikaze, deliberately sacrificed herself by intercepting the torpedoes and sank with no survivors.

[19] While returning from Manila, Jun'yō was attacked by the submarines Sea Devil, Plaice and Redfish early in the morning of 9 December 1944.

[19] The repairs were abandoned in March 1945 for lack of materials and the ship was moved from the dock to Ebisu Bay, Sasebo on 1 April.