(KS type RO-109 scanned from "Submarines of the Imperial Japanese Navy" by Polmar and Carpenter)

IJN Submarine RO-100:
Tabular Record of Movement

© 2001-2017 Bob Hackett & Sander Kingsepp
Revision 3

30 June 1941:
Kure. Laid down at Kure Navy Yard as a 525-ton (standard) Kaisho (KS) Type submarine No. 210.

6 December 1941:
Launched as RO-100.

30 May 1942:
Lt (later LtCdr) Sakamoto Kaneyoshi (61)(former torpedo officer of I-1) is appointed the Chief Equipping Officer (CEO).

25 July-29 August 1942:
Lt Sakamoto is appointed the CEO of RO-103, also under construction at Kure, as an additional duty.

23 September 1942:
Completed and attached to Yokosuka Naval District. Assigned to Rear Admiral (later Vice Admiral), the Marquis, Daigo Tadashige's (former CO of ASHIGARA) Kure SubRon for working-up. Lt Sakamoto Kaneyoshi (later Rear Admiral, JMSDF) is the Commanding Officer.

15 December 1942:
Reassigned to Rear Admiral (later Vice Admiral) Harada Kaku's (former CO of CVS CHIYODA) SubRon 7 in Vice Admiral Mikawa Gunichi's (former CO of KIRISHIMA) Eighth Fleet.

20 December 1942:
Departs Yokosuka for Truk.

28 December 1942:
Arrives at Truk.

6 January 1943:
Departs Truk for Rabaul, but is forced to return on the following day as a result of diesel engine breakdown.

3 February 1943:
Departs Truk for Rabaul.

6 February 1943:
Bismarck Sea, NW of Rabaul. In the afternoon, RO-100 is bombed by an Aichi E13A1 "Jake" patrol floatplane. The damage is minor.

7 February 1943:
Arrives at Rabaul.

8 February 1943:
Departs Rabaul on her first war patrol to patrol in the Coral Sea off Port Moresby, New Guinea.

14 February 1943:
40 miles SSW of Port Moresby. After 1630, Lt Sakamoto sights an enemy convoy and begins a submerged approach at 2.5 knots to gain attack position. Engrossed with his target, Sakamoto fails to sweep the surrounding seas with his periscope. A destroyer approaches RO-100 unseen until the last moment. RO-100 manages to crash-dive to 140 feet.

The attacker drops over a dozen depth charges. Several leaks emerge in the main engine room and the conning tower. In addition, both of her periscopes are rendered inoperative. As a result of the attack, the submarine assumes a steep up-angle. To prevent diving to crushing depth, Sakamoto orders every avaliable man to the forward torpedo room.

20 February 1943:
Returns to Rabaul for battle-damage repairs. During that period several officers are replaced.

1 April 1943: Operation "I-GO" - The Reinforcement of Rabaul:
Admiral (Fleet Admiral, posthumously) Yamamoto Isoroku (former CO of AKAGI), CINC Combined Fleet, orders aircraft from CarDiv 1's ZUIKAKU and the ZUIHO to reinforce Vice Admiral Kusaka Jinichi's (former CO of FUSO) 11th Air Fleet's base at Rabaul. Yamamoto also orders aircraft from CarDiv 2's HIYO and JUNYO to reinforce the base at Ballale Island, near Buin, Bougainville.

RO-100 departs Rabaul to patrol SE of Guadalcanal in support of the "I-GO" operation. Soon after arrival, the gyrocompass breaks down and the patrol has to be aborted.

12 April 1943:
Returns to Rabaul.

22 April 1943:
Departs Rabaul to patrol SE of Guadalcanal on her second war patrol.

14 May 1943:
Returns to Rabaul.

27 May 1943:
Departs Rabaul on her third patrol SE of Guadalcanal.

20 June 1943:
Returns to Rabaul.

30 June 1943:
American Operation "TOENAILS" - The Invasion of New Georgia, Solomons: Rear Admiral (later Admiral) Richmond K. Turner's Third Fleet Amphibious Force, supported by land-based aircraft, lands Marines and Army troops on Rendova and other islands in the New Georgia area. After receiving a sighting report from RO-101, Rear Admiral Harada orders RO-100, RO-106 and RO-107 to take up positions in Blanche Channel to intercept Amerian reinforcements.

2 July 1943:
RO-100 departs Rabaul on her fourth patrol to an area SE of Rendova's anchorage.

Early July 1943:
Blanche Channel, New Georgia Island. At night, while reconnoitering the American airfield at New Georgia Island by periscope, Lt Sakamoto grazes a reef and damages two of RO-100's bow tubes and a fuel tank. He reports the damage to Rabaul and is ordered to return after picking up IJNAF pilots stranded at Simbo Island, Western Solomons.

Mid-July 1943:
After rescuing several pilots from the 201st and 204th NAG, the RO-100 delivers them to Buin, then departs for Rabaul.

12 July 1943:
Returns to Rabaul.

7 August 1943:
Departs Rabaul for New Guinea. Soon after departure, a leak from the previously damaged oil tank is discovered and RO-100 turns back.

8 August 1943
NE of Buka Island. While running surfaced, RO-100 is attacked by an unidentified submarine which misses her with four torpedoes.

Off Cape St. George, New Ireland. At night while running surfaced, RO-100 is suddenly illuminated by flares dropped by a patrol plane, probably a PBY "Catalina" from either VP-12 or VP-54. The "Catalina" misses the submarine with two bombs and strafes her. Lt Sakamoto crash-dives.

11 August 1943:
Returns to Rabaul for repairs.

Mid-August 1943:
Departs Rabaul on her fifth war patrol.

20 August 1943:
Reassigned to SubDiv 51.

30 August 1943:
Lt (LtCdr, posthumously) Seki Noritaka (63)(former torpedo officer of I-177) is appointed the CO.

Early September 1943:
Returns to Rabaul.

7 September 1943:
Departs Rabaul on her sixth war patrol to the area N of New Guinea.

10 September 1943:
Lt (LtCdr, posthumously) Okane Hisao (63)(former torpedo officer of I-10) is appointed the CO.

18 September 1943:
Returns to Rabaul, later proceeds to Truk.

30 September 1943:
Truk. Dry-docked in a floating dock.

1 November 1943: American Operation "SHOESTRING II" - The Invasion of Bougainville:
Rear Admiral (later Vice Admiral) Theodore S. Wilkinson's Third Amphibious Force, Task Force 31, lands LtGen (later Gen/Commandant/MOH) Alexander A. Vandegrift's 1st Marine Amphibious Corps at Cape Torokina, Empress Augusta Bay, Bougainville, Solomons.

10 November 1943:
Departs Truk on her seventh patrol to patrol in the Bougainville area.

19 November 1943:
Arrives at Rabaul. Embarks a cargo of food in rubber containers.

23 November 1943:
At 0500, departs Rabaul on an emergency supply run to Buin, Bougainville.

25 November 1943:
Bougainville Strait, two miles W of Oema Island. At 1910 (local), when the surfaced RO-100 is navigating the N channel to Buin at 06-50S, 155-58E, a mine explodes beneath her port side amidships hull. The explosion throws Lt Okane and the lookouts standing on the bridge into the sea. RO-100's engineering officer gives the order to abandon the rapidly sinking submarine. While trying to reach Buin, some survivors are attacked by sharks. Of 50 crewmen, only 12 survive.

5 February 1944:
Removed from the Navy List.

Authors' Notes:
Thanks go to Dr. Higuchi Tatsuhiro of Japan and to Mr. Jean-François Masson of Canada.

– Bob Hackett and Sander Kingsepp.

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