© 1998/2006 Anthony P. Tully

Initial Command Structure:
Commanding Officer: Captain Beppu Akitomo. Assigned to CarDiv 1, Third Fleet.

31 July 1942:
Commissioned at Kure. Assigned to CarDiv 2, Third Fleet.

12 August 1942:
Receives the flag of Rear Admiral Kakuta Kakuji, ComCarDiv 2, Third Fleet.

4 October 1942:
Depart Saeki for Truk.

9 October 1942:
Arrive at Truk. Assigned to Main Unit Advance Force (CarDiv 2, Third Fleet).

11 October 1942:
Depart Truk in the preliminaries to the Battle of Santa Cruz.

17 October 1942:
While operating off Guadacanal prior to the Battle of Santa Cruz, a fire breaks out in the generator room. Considerable damage to the condensor is caused and the carrier is slowed to 16 knots. Due to this, after transferring Radm Kakuta Kajuji's (ComCardiv 2) flag and a portion of her aircraft to JUNYO, she heads back to Truk for repairs.

26 October 1942:
Arrive at Truk for repairs.

13 November 1942:
`Minor' bomb damage received while at Truk.

27 November 1942:
`Minor' bomb damage again listed for air raid on Truk.

30 November 1942:
Captain Beppu relieved by Captain Sumikawa Michio as commanding officer.

5 December 1942:
Reassigned to Mobile Force. Depart Truk for Kure.

11 December 1942:
Arrive at Kure from Truk via Saeki.

15 January 1943:
Assigned to Mobile Force, Stand-by Force (CarDiv 2, Third Fleet). In and out of Tokuyama frequently, remaining in the Inland Sea throughout January and February.

26 February 1943:
Enter drydock at Kure.

4 March 1943:
Leave Kure drydock, and resume movements between Kure and Tokuyama.

22 March 1943:
Depart Saeki for Truk, reassigned to Main Unit Mobile Force.

27 March 1943:
Arrive at Truk.

1 April 1943:
Assigned to contribute aircraft to "I" Operation activated by Commander-in-Cheif Yamamoto Isoroku this day. Vessel itself remains at Truk.

12 April 1943:
Minor damage from splinters from air raid on Truk.

17 May 1943:
Depart Truk as part of the general exodus of Combined Fleet back to home waters following the death of C-in-C Yamamoto on 18 April 1943.

21 May 1943:
Arrive at Yokosuka. Reassigned from Advance Force to Main Body of Mobile Force.

25 May 1943:
Arrive at Kisarazu.

2 June 1943:
Arrive Yokosuka; returns to Kisarazu on the 5th.

7 June 1943:
Arrive back at Yokosuka from Kisarazu.

10 June 1943:
Flying the flag of ComCarDiv 2 Radm Sakamaki Mumetaka - departs Yokosuka for Truk escorted by destroyers ARIAKE and YUGURE. However, prior to 2000 hours in position bearing 64 degrees 17 miles from Miyake Island was hit by two torpedoes in the starboard bow and boiler rooms fired by the U.S. submarine TRIGGER. Boiler rooms No. 1 and No. 2 are flooded and all of the former and half of the latter's engineers killed. The carrier goes dead in the water and settles by the bow. However, good damage control keeps her afloat all through the long night that follows. The next morning, light cruiser ISUZU comes out to tow, but the carrier is already back under her own power, and returns to Tateyama by midnight of the 11th using two screws.

12 June 1943:
Moves over to Yokosuka.

15 June 1943:
While their ship is under repair, HIYO's aircraft (21 fighters, 9 attack, 18 bombers) and crew assigned to temporary duty on the light carrier RYUHO.

29 June 1943:
Enters drydock for repairs at Yokosuka.

31 August 1943:
HIYO's crew returns to their ship from the RYUHO as repairs near completion.

1 September 1943:
Captain Furukawa Izumi assigned as commanding officer.

15 September 1943:
Leaves Yokosuka drydock, repairs complete. The same day, the aircraft of CarDiv 2 are staging on land at Tusiki and Iwakuni.

5 October 1943:
Aircraft of CarDiv 2 fly south to Singapore, and soon HIYO is ordered south to rejoin them.

29 October 1943:
Arrive at Kure from Yokosuka.

24 November 1943:
Depart Inland Sea for Singapore via Manila.

29 November 1943:
Arrive at Manila for overnight stay; next day departs for Singapore.

3 December 1943:
Arrives at Singapore.

9 December 1943:
Assigned to aircraft ferry duty, depart Singapore for Truk; with stops at Tarakan (145h/15th); and Palau (18th/19th).

22 December 1943:
Arrive at Truk.

27 December 1943:
Depart Truk for Saipan ferrying aircraft.

29 December 1943:
Arrive at Saipan.

15 February 1944:
Captain Furukawa releived of command. Captain Yokoi Toshiyuki takes his place as commanding officer the next day.

11 May 1944:
In company with sister ship JUNYO, the MUSASHI, ZUIHO, CHITOSE, and CHIYODA; depart Saeki, Japan for Tawi Tawi.

12 May 1944:
Stopover at Okinawa.

16 May 1944:
Arrive at Tawi Tawi.

19 - 20 June 1944:
Participate in the Battle of the Marianas, launching strikes. On 20 June while sailing with JUNYO and RYUHO, covered by NAGATO and MOGAMI with a destroyer screen at 1745 comes under attack by dive-bombers and torpedo planes. One small bomb dropped by a plane from USS ENTERPRISE's Air Group 10 graze the foremast and exploded above the top of the bridge, showering it with fragments. Captain Yokoi is wounded, and the Navigator and Air Officer and nearly all bridge personnel killed. Another bomb is repoted to have exploded on the flight deck. Just afterward six torpedo planes from USS BELLEAU WOOD Air Group 24 drove in for an attack (U.S. records say it was four planes led by Lt (jg) George Brown). Two were shot down, and three dropped their weapons too far away, but one badly hit and burning TBF "courageously closed to most favorable angle and range" and dropped his torpedo which struck the starboard engine room. The burning plane then hurtled by the island and crashed into the sea. (Note 1). With the starboard engine flooding, white steam belched out of HIYO'S funnel and she began to lose speed rapidly, but continued to steam on her port shaft. Her sister carrier JUNYO closed for a brief time, but was urged to proceed on. Fires had broken out, but were believed to be under control and the list checked. The original course was resumed and the HIYO commenced to retire with the others. However, nearly two hours after the initial hit, there was tremendous explosion that erupted from the port quarter. A torpedo from an enemy submarine was believed responsible. (Note 2). This explosion damaged the main switchboard panel and stopped all power generation. Leaking gas was set off and flames engulfed the whole rear of the ship. Destroyer URANAMI closed the port quarter to assist, but the fire raged and explosions mounted with increasing damage. The HIYO began to settle by the stern and list to port , which was indicative of the force of the major explosion that had ripped through her earlier.

Sunk: At 1932 mortally stricken, and settling fast now, HIYO rears her bow skyward and sinks stern first. (Note 3) Lost with her are 247 officers and men, but Captain Yokoi is picked up by MICHISHIO, and a 1,000 of her crew are rescued by destroyers SHIGURE, MICHISHIO, HAMAKAZE, HAMANAMI, AKISHIMO, and HAYASHIMO.

30 June 1944:
Captain Yokoi Toshiyuki formally released as commanding officer.

10 November 1944:
Removed from Navy List.

Note 2: To date, this Japanese claim of a submarine torpedo hit on HIYO had been confusing, and imagined perhaps to be the result of the traumatic experience of the sinking of both TAIHO and SHOKAKU by submarine just the day before. However, IJN official sources always credited a submarine torpedo, and Captain Yokoi's report is the reason. Instead, what clearly happened was a massive induced explosion that doomed salvage efforts and fatally wounded the vessel. This makes HIYO one of three Japanese fleet carriers sunk by the same combination of petrol tank vapor and induced explosion within a 48 hour period.

Note 3: In April 1997, while struggling with the conflicting and scarce reports of HIYO's final sinking, I authored an article exploring the discrepancies and addressing whether HIYO went down bow first, or stern first. I opted for stern first, but this was necessarily tentative. New sources consulted since then have affirmed this, and indicate that HIYO indeed went down stern first, or , just possibly, broke in half! The article related to this, has been taken offline as a result, pending revision.(A.Tully)