© 2001 Anthony P. Tully
© Revised-Jan 2012 Anthony P. Tully

Contact Email tullyfleet - gmail.com

31 May 1942:
Liner YAWATA MARU recommissioned at Kure after conversion to escort carrier after having been officially requisitioned for conversion. Attached to Combined Fleet. Captain Minato Keisho serving as commanding officer.

25 July 1942:
Depart Kure for Yokosuka.

29 July 1942:
Depart Yokosuka for what will be the first of many plane-ferrying and supply trips to Truk and outer bases.

31 July 1942:
YAWATA MARU's name offically changed to UNYO.

2 August 1942:
Arrive at Saipan.

9 August 1942:
Arrive at Ulithi, depart next day.

14 August 1942:
Arrive at Kure.

31 August 1942:
? assigned as commanding officer.

1 September 1942:
Depart Kure.

2 September 1942:
Arrive at Yokosuka.

4 September 1942:
Depart Yokosuka.

7 September 1942:
Arrive at Saipan, depart next day.

9 September 1942:
Arrive at Truk.

11 September 1942:
Arrive at Rabaul with 10 A6M3/32s.

13 September 1942:
Depart Truk.

18 September 1942:
Arrive at Yokosuka.

25 September 1942:
Depart Yokosuka.

1 October 1942:
Arrive at Truk.

4 October 1942:
Depart Truk.

9 October 1942:
Arrive at Yokosuka.

11 October 1942:
Depart Yokosuka.

16 October 1942:
Arrive at Truk; depart next day to return to Yokosuka.

24 October 1942:
Arrive at Yokosuka.

28 October 1942:
Depart Yokosuka.

2 November 1942:
Arrive at Truk, depart next day for Palau.

8 November 1942:
Arrive at Palau.

11 November 1942:
Depart Palau.

13 November 1942:
Arrive at Davao.

15 November 1942:
Arrive at Palau.

16 November 1942:
Depart Palau.

21 November 1942:
Arrive at Truk.

24 November 1942:
Depart Truk.

2 December 1942:
Arrive at Surabaya.

5 December 1942:
Depart Surabaya.

6 December 1942:
Arrive at Balikpapan, depart next day for Truk.

13 December 1942:
Arrive at Truk. Offloads the 11th Fighter Regiment embarked at Surabaya.

17 December 1942:
Depart Truk.

24 December 1942:
Arrive at Surabaya.

26 December 1942:
Depart Surabaya. Pick up thirty-three aircraft of the Army's 1st Fighter Regiment for delivery to Truk.

28 December 1942:
Arrive at Balikpapan, depart next day for Truk.

3 January 1943:
Arrive at Truk.
5 January 1943:
Depart Truk for Yokosuka.

18 January 1943:
Enter drydock at Yokohoma.

24 January 1943:
Leave drydock, move from Yokohoma to Yokosuka.

28 January 1943:
Captain Aitoku Ichiro assigned as commanding officer.

1 February 1943:
Depart Yokosuka. Embarked are 36 twin-engine Ki-48 II Type-99 (Lily) bombers of the Army's 208th Light Bomb Regiment.

7 February 1943:
Arrive at Truk.

11 February 1943:
Depart Truk with TAIYO.

17 February 1943:
Arrive at Yokosuka with TAIYO and HIBIKI.

24 February 1943:
Depart Yokosuka with TAIYO for Truk, escorted by HIBIKI.

2 March 1943:
Arrive at Truk.

6 March 1943:
Depart Truk for Yokosuka with TAIYO, escorted by USHIO and HIBIKI.

12 March 1943:
Arrive at Yokosuka.

20 March 1943:
Depart Yokosuka.

25 March 1943:
Arrive at Truk.

5 April 1943:
Depart Truk.

10 April 1943:
Arrive at Yokosuka.

14 April 1943:
Captain Seki Ikuya becomes commanding officer.

25 April 1943:
Depart Yokosuka for Truk with both TAIYO and CHUYO, escorted by SHIGURE and NAGANAMI.

30 April 1943:
Arrive at Truk.

8 May 1943:
Depart Truk for Yokosuka with TAIYO.

13 May 1943:
Arrive with TAIYO at Yokosuka, both carriers turn around and depart again for Truk on 24 May.

29 May 1943:
Arrive with CHUYO at Truk.

5 June 1943:
Depart Truk accompanying CHUYO for Yokosuka, arriving on the 9th.

16 June 1943:
Depart Yokosuka with RYUHO and CHUYO for Truk.

21 June 1943:
Arrive at Truk, depart to Yokosuka on 28 June, arriving with CHUYO 2 July at Yokosuka.

6 July 1943:
Depart Yokosuka for Truk. Embarked aboard UNYO are contingents of the 552nd and 201st Naval Air Groups.

10 July 1943:
- Dusk, north of Truk, having been joined by AIKOKU MARU, the ships are closed by a submarine wolf pack. At 2032 (King time) in position 10-37'N, 150-45'E the AIKOKU MARU is hit in the port side aft by one torpedo. She is left limping and down by the stern.
- 1348 (G.C.T. time/2348 local, which is? ) In position 10-00'N, 150-48'E UNYO is attacked by USS STEELHEAD (SS-28), which fires five torpedoes at UNYO's port side in a shot at 1,900 yards. Claims two hits at properly timed intervals, and seeing "a momentary dull orange glow on the port side of the target aft at the waterline." Not only that, the submarine claimed seeing smoke rise in the air, and the XCV turn away and apparently stop and seem to be listing 10 degrees to port. An ACL (AIKOKU MARU??) that seemed to be damaged was present as well. Ultra seems to confirm the attack, as UNYO reports sighting four torpedoes. No damage. As first sighted, seemed to be one large vessel "an AP or auxiliary CL" and three escorts.[Note -- Hackett & Sander TROM for AIKOKU MARU credits the hit to HALIBUT and times it to about 2100; therefore, though what the STEELHEAD observes sounds remarkably similar, this accreditaton remains more likely.]

11 July 1943:
Arrive at Truk with the limping AIKOKU MARU.

19 July 1943:
Depart Truk with RYUHO and CHUYO for the homeland, arriving at Yokosuka on 24 July. A rest is now taken, the ship remaining home through the end of the month.

31 July 1943:
Depart Yokosuka for Truk with NAGARA and screened by AKEBONO, USHIO, and SHIRATSUYU.

4 August 1943:
1644 (G.C.T. time) TAIYO or UNYO attacked in position 08-15'N, 150-07'E by USS STEELHEAD which fires six torpedoes at the starboard sides of a CVE and BB at long-range of 7,400 yards, claiming two possible hits. The submarine reported that it was a large force of four big ships in column, two possible cruisers, followed by BB and CVE. Three DDs out in front, and one on each flank.

5 August 1943:
Arrive at Truk.

12 August 1943:
Depart Truk for Yokosuka.

16 August 1943:
Arrive at Yokosuka.

26 August 1943:
Depart Yokosuka for Truk.

2 September 1943:
Arrive at Truk.

6 September 1943:
Depart Truk for Inland Sea.

11 September 1943:
Arrive at Kure.

30 September 1943:
Enter drydock at Kure.

9 October 1943:
Leave dock.

13 October 1943:
Depart Kure for Truk.

21 October 1943:
Arrive at Truk.

30 October 1943:
Depart Truk for Yokosuka.

5 November 1943:
Arrive at Yokosuka. Depart Yokosuka with ZUIHO and CHUYO for Truk; arriving there on 21 November.

30 November 1943:
Depart Truk for Yokosuka as part of a task force led by ZUIHO, and comprised also of CHUYO and MAYA, and escorted by AKEBONO, SAZANAMI, URAKAZE, and USHIO. Aboard the CHUYO and UNYO are twenty-one and twenty POWs respectively from USS SCULPIN, sunk 19 November by YAMAGUMO.

4 December 1943:
Approaching Izu Island, task force is attacked by USS submarine SAILFISH. The CHUYO is torpedoed and finally sunk in a series of three attacks at 0010, 0555, and 0942. Although initially ordered to tow the torpedoed CHUYO, the UNYO is then told to proceed to Yokosuka.

5 December 1943:
Arrive at Yokosuka. Assigned from Combined Fleet Force to Grand Escort Command.

12 December 1943:
Depart Yokosuka for Truk.

17 December 1943:
Arrive at Truk.

24 December 1943:
Depart Truk for Yokosuka.

29 December 1943:
Arrive at Yokosuka.

4 January 1944:
Depart Yokosuka for Truk with ZUIHO, HATSUSHIMO, HATSUHARU, and WAKABA.

9 January 1944:
Arrive at Truk.

18 January 1944:
- 0415 HAYANAMI departs Truk to carry out anti-sub sweep ahead of them, then UNYO with ZUIHO, NOSHIRO, HATSUSHIMO and WAKABA depart Truk for Japan.

19 January 1944:
At 1143 [King-time] in position 12-12'N, 146-26'E 140 miles east-southeast of Guam, UNYO is attacked by USS HADDOCK (SS-231)which fires six torpedoes at her port side. They are detected and apparently UNYO has time to almost comb them, for reportedly three torpedoes hit her fine on the starboard side forward; one a dud. One struck in way of the fresh water tanks, and two in the forward gasoline tanks (under the bridge) but the tanks simply flood, apparently empty. In any case they do not explode. The bow structure is badly damaged and sags downward at frame 177, but she is able to remain underway. HAYANAMI drops depth charges, while ZUIHO proceeds for Japan. NOSHIRO, HATSUSHIMO, and WAKABA shepherd the crippled CVE toward shelter at Saipan.[Note 1]

20 January 1944:
UNYO arrives at Saipan Island for emergency repairs. However the harbour is small and the carrier has to drop anchors outside the harbour, in the open roadstead. The 5th Base Force there has few facilities and few artisans. HATSUHIMO remains outside the anchorage on patrol duty, soon joined by HAYANAMI. The days that follow see destroyers patrolling outside the small anchorage to ward off prowling enemy submarines.

23 January 1944:
1135 [King-time] USS HALIBUT moves in close to Saipan outer harbor and spots UNYO anchored there at 15-11'N, 145-41'E. But close air and surface patrols prevent making any attack approach.

25 January 1944:
Temporary pumping out and shoring up repairs on UNYO's foresection completed.

27 January 1944:
0518 UNYO creeps out from the Saipan roadstead escorted by HATSUSHIMO, AKEBONO, and USHIO. The patrolling SATSUKI joins them as they head north with the carrier at slow speed, no more and often less than 12 knots.

31 January 1944:
1320-28 USHIO and SATSUKI drops d/c on suspected sub contact.

1 February 1944:
Cruiser TAKAO and destroyer TAMANAMI join to shepherd the UNYO group on approach to Yokosuka, having detached from force built around ZUIHO and CHIYODA outbound for Truk. TAMANAMI soon detached to return to CHIYODA task force.

2 February 1944:
- 0753 USS GUDGEON (SS-211_ reports sighting UNYO, three DDs and one unidentified, probably a minelayer.
1010-1016 AKEBONO sights a periscope (GUDGEON) avoids two torpedo tracks and drops 22 d/c. SATSUKI participates.[The submarine counted 31 depth-charges] Though she fires at the destroyers and misses, GUDGEON is forced away without being able to attack the crippled escort carrier. The same happens to USS SAURY (SS-189), attempting to close the base course at the same time from the west.[Note-2]

3 February 1944:
1710 SATSUKI detaches from the formation but other ships are sailing out from Yokosuka to meet them.

4 February 1944:
1320 SHIRAKUMO joins the UNYO caravan. This afternoon, not far out from Sagami and Tokyo Bay area, the UNYO group runs into a severe storm. The suspended foresection soon snaps off completely, causing the flight deck forward to collapse over the stunted forepart. To lessen the pressure on the weakened forward bulkheads, it proves necessary for the skipper to turn the carrier around and steam backward. The storm rages through the 6th, and progress is excruciatingly slow, only a few knots.[Note-3]

5 February 1944:
0645 SHIRAKUMO is released from escort duty and detaches, resuming her voyage to Ominato.
0900 KISHINAMI joins the UNYO group having come out from Kure.
TAKAO detaches and proceeds ahead with AKEBONO, USHIO and HATSUSHIMO to Yokosuka to refuel.

6 February 1944:
AMAKUSA and SATSUKI joins the UNYO group. Later afternoon, USHIO and AKEBONO join up too.

7 February 1944:
Having refueled, cruiser TAKAO rejoins the crippled carrier and her escorts and remains with her for the last leg. HATSUSHIMO also joins. At 0800 for about an hour SATSUKI and HATSUSHIMO drop depth charges outside the bay on suspected sub contacts.
- UNYO pauses to anchor near Tateyama while TAKAO and the various destroyers proceed independently.

8 February 1944:
UNYO arrives at Yokosuka. The drama and dramatic slow crawl to home from Saipan is over. Repairs commence.

1 March 1944:
Captain Seki releived by Captain Hiratsuka Shiro.

2 April 1944:
Enter drydock for full repairs.

28 June 1944:
Leave drydock, repairs complete.

1 July 1944:
Captain Hiratsuka relieved by Captain Kimura Ikuzo as commanding officer.

12 August 1944:
Depart Yokosuka for Inland Sea with YAMASHIRO and DesDiv 21 (HATSUHARU, WAKABA.)

13 August 1944:
Arrive at Kure.

14 August 1944:
Assigned to the 1st Surface Escort Force.

25 August 1944:
Depart Moji with light cruiser KASHII escorting HI-73 convoy with six escorts to Seletar.Ten Type 97 attack planes and six Type 93 bi-planes training aircraft from the 931st Squadron are embarked.

5 September 1944:
Arrive at Singapore.

11 September 1944:
Depart Seletar with light cruiser KASHII escorting convoy HI-74 of five tankers with six escorts for Moji.

17 September 1944:
At 0034 tanker AZUSA MARU is hit in starboard side by two torpedoes and bursts into flames and sinks in fifteen minutes. Alerted by the attack, UNYO's soundgear detects torpedoes and she attempts to evade. But at 0037 is hit in the starboard side by two torpedoes from USS BARB (SS-220), one in the stern in the steering compartment, the other in the engine room, killing twenty-six men. The escort carrier goes dead in the water. Although the damage was severe and the UNYO settled aft, her crew set to work, and it seemed she might be saved. At 0142 she radios "Torpedo attack, two torpedoes, damage sustained." Sinking was not expected. However, the sea conditions worsened, pounding hard at the fantail, and collapsing the emergency reinforcements to the bulkheads. By 0730 she was listing heavily to starboard, and the order was given to abandon ship. At 0755 the UNYO sank by the stern in position 19-10'N, 116-35'E (Radio notice at 0805 gives slight variant of 19-08'N, 116-36'E.") Working hard in the stormy seas, the escorts CHIBURI and CD # 27 rescued 55 officers, and 706 men, but Captain Kimura Ikuzo went down with his ship. [Note-4].

10 November 1944:
Removed from the Navy list.

Note 2:
It would appear that Pearl Harbor was not entirely satisfied that either HALIBUT's or GUDGEON's attack attempts had been pressed home with due ardor, given such a valuable and vulnerable target. The patrol report endorsements of both subs for these state rather bluntly they are "not considered successful for combat insignia award."

Note 3:
There is a series of photographs - some with a destroyer alongside - commonly identified as the torpedoed CHUYO on the morning of 4 December 1943. However a surprise comes from Katsura Rihei, author of a book on ZUIHO, who has done some research. Katsura found that the photos were taken by a plane out of Tateyama flown by Lt.Cdr. Furukawa of the 452nd Air Group. He took them on 4 or 5 February 1944 when UNYO was struggling through the stormy seas off Tateyama after her bow had further broken down. We see just such damage under the forward struts of the flight deck and the bow clearly missing and it is revealed she is steaming slowly backwards. In every respect the photos match the circumstances of UNYO's drama, and the disconnects with CHUYO's conditions are explained - it is not her at all. (It is worth noting that a thread on J-Aircraft.com had noticed a discrepancy in the secondary guns that hinted of this possibility. The carrier in the photo has AA armament like TAIYO's, while CHUYO had four dual-mount 12.7 cm AA. The key was learning that UNYO suffered similar bow damage to torpedo.) [In this connection it is also worth noting that a thread on J-Aircraft.com on Dec 28, 2008 identified seven Ki-61 Hien aircraft with one single Ki-45 Toryu aircraft up forward on what was then thought to be crippled CHUYO in the photos. Now that they are correctly associated with damaged UNYO they speak of her load at the time.]

Note 4:
Accounts conflict, or appear to, about UNYO's casualties. According to UNYO's Action Report in November 1944 she had 45 officers and 781 men as wartime complement. Though all sources agree that 761 survivors were rescued, some allege that nearly 1,000 passengers were aboard at the time, and of these, more than 800 perished. This seems like a rather high figure, and another Japanes source, a roster of casualties, gives "most were saved" and 750+ as the figure. Regarding this discrepancy it appears that an alternate reading gives a total of about 1,000 aboard counting crew and passengers . This would make about 200 lost, which incidentally is the rendering chosen by Admiral Fluckey in his superb 1992 book, Thunder Below . An update will be posted upon verification of the correct figures.
- Remark: as of August 2010 it has thus far proven impossible to settle the discrepancy of the loss figures. However, an ominous clue suggests the total loss among passengers may have indeed been high. Despite the fact that UNYO floated so long, the critical fact is that the final order to Abandon Ship was given only a short time before her sinking. If transfers of crew were not in progress prior -- and the storm calls this into question -- then the opportunity to easily evacuate proved as limited as that of a swift foundering would be. According to one soldier's eyewitness account, the upending came suddenly and in some cases rescue took as long as four hours. If this surmise is correct, if a large number of passengers was aboard, they most likely indeed, perished, thus explaining the high figure.- (Tully)