|Ship Class||Hiyo-class Escort Carrier|
|Laid Down||30 Nov 1939|
|Launched||24 Jun 1941|
|Commissioned||31 Jul 1942|
|Sunk||21 Jun 1944|
|Displacement||26949 tons standard|
|Power Output||56520 SHP|
|Armament||12x130mm guns, up to 76x25mm anti-aircraft guns, 6x130mm anti-aircraft rockets (post-1944)|
Contributor: C. Peter Chen
Hiyo was the lead ship of her class of aircraft carriers. She was originally laid down as the passenger liner Idzumo Maru by Nippon Yusen Kaisha (Japan Mail Steamship company), and was purchased by the Japanese Navy in 1940 for conversion into an aircraft carrier. Although originally destined for Carrier Division 1, upon completion she was assigned to Carrier Division 2, 3rd Fleet instead. On 12 Aug 1942, she became the flagship of Rear Admiral Kakuji Kakuta of Carrier Division 2. On 4 Oct, she departed for Truk, Caroline Islands in the Central Pacific, arriving on 9 Oct. Two days later, she departed for the Solomon Islands for what would become the Battle of Santa Cruz, but while operating off Guadalcanal on 17 Oct, a fire broke out in the generator room; with her speed down to 16 knots, she was sent back to Truk for repairs, thus missing the battle. Repairs began on 26 Oct, and on 13 and 27 Nov, while still under repair, American carrier aircraft attacked Truk, causing minor damage on Hiyo on both dates. On 30 Nov 1942, Captain Michio Sumikawa was assigned to the ship. On 5 Dec, she departed Truk, arriving in Kure, Japan on 11 Dec. Between 26 Feb and 4 Mar, she was in the drydock at Kure. On 27 Mar 1943, she was back in Truk. On 12 Apr, she was damaged by an air raid. On 17 May, she left for Japan as the Combined Fleet evacuated Truk, arriving at Yokosuka, japan on 21 May.
On 10 Jun 1943, while off Miyake Jima off southeastern Honshu, Japan, Hiyo was struck in the starboard side by two torpedoes from American submarine USS Trigger. The boiler rooms No. 1 and 2 were flooded, killing a great number of engineers and rendering the ship dead in the water. On the next day, cruiser Isuzu arrived to tow her to port, but by that time Hiyo had already restored partial power so that she could return to Tateyama on her own. After being moved to Yokosuka, she was repaired between 15 Jun and 15 Sep 1943; while under repair, her 48 aircraft were transferred to light carrier Ryuho. On 1 Sep, also while under repair, Captain Izumi Furukawa was assigned as her commanding officer.
Between Oct and Dec 1943, Hiyo ferried aircraft from Japan to Singapore, Truk, and Saipan of Mariana Islands. On 15 Feb, Captain Toshiyuki Yokoi took command of the ship.
At 1745 on 20 Jun 1944, while sailing with Junyo and Ryuho and covered by Nagato and Mogami, she came under attack by American aircraft during the Battle of the Philippine Sea. A bomb dropped by a dive bomber from USS Enterprise's Air Group 10 exploded above the bridge, wounding Captain Yokoi and killing most of the bridge personnel. Another bomb exploded on the flight deck. Soon after, six TBF Avenger torpedo bombers from USS Belleau Wood attacked her; two were shot down, but one of the torpedos dropped hit the starboard engine room. The engine room flooded, slowing her down. Fires were reported but were initially believed to be contained. The fire, however, led to an explosion in the port quarter, which ignited gas vapors in the entire rear of the ship. She began to settle by the stern with an increasing list to port. She sank at 1932. 247 men were lost, while 1,00 were rescued by destroyers, including Captain Yokoi.
To date, official Japanese reports still note that the cause of the final explosion that led to her sinking was caused by another American torpedo. This was due to Yokoi's post-battle report that noted so, probably in error.
Hiyo Operational Timeline
|31 Jul 1942||Hiyo was commissioned into service.|
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