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  Aikoku Maru 愛国丸
Armed Merchant Cruiser

10,437 Tons
527' 7" x 66' 3" x 28' 10"
4 x 150mm guns
2 x 80mm guns
2 x 4 13mm AA guns
2x4 torpedo tubes
2 x E7K Alf floatplanes

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OSK 1941

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IJN 1942

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IJN 1944

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Peter Ording 2000
Ship History
Built by Mitsui Engineering & Shipbuilding at the Tamano shipyards in Okayama, Japan. Purchased by the Osaka Shosen KK (OSK Line) with Japanese government subsidies as a combined luxury passenger liner and cargo vessel for South America and around the world service. The vessel was provisionally named "Kyoto". Laid down December 29, 1938. Launched April 25, 1940 and named "Aikoku Maru". Completed August 31, 1941 immediately requisitioned by the Imperial Japanese Navy (IJN).

Wartime History
Starting on September 5, 1940 converted into an armed merchant cruiser at Tamano shipyards. Anti-aircraft guns, 1100mm and 900mm searchlights and a boom were installed for two E7K Alf reconnaissance float planes. The conversion was completed by October 15, 1942 and assigned to the 24th Squadron (Raider) under Rear Admiral Takeda Moriji and attached directly to the Combined Fleet, CruDiv 24 with Hokoku Maru and Kiyosumi Maru.

On October 31, 1941 departs Okayama bound for Kure.


On April 30, 1942 arrives Penang with Hokoku Maru to support SubRon 8 "KO" (A) detachment submarines I-10, I-16, I-18, I-20 and I-30 for operations in the western Indian Ocean. On May 5, 1942 departs Penang with Hokoku Maru.


On April 5, 1943 assigned to Captain Shojiro Mizusaki.


On October 20, 1943 assigned to captain Yoshizo Nakamaruo.


On February 16, 1944 anchored in Truk Lagoon inside the 4th Fleet anchorage on the east side of Dublon Island. Immediately, the ship began loading munitions bound for Rabaul. Aboard were 400 troops from Japanese Navy 1st Amphibious Brigade who were billeted in the aft cargo hold no. 4, which was converted into makeshift quarters.

Sinking History
On February 17, 1944 at 8:15am Aikoku Maru was attacked by US Navy carrier aircraft from USS Intrepid CV-11. During the attack, a bomb hit the officer's wardroom galley and starts a fire that spreads quickly. Other aircraft score three additional bomb hits.

At roughly 8:30am, TBM Avenger 25270 dropped an aerial torpedo that impacted the ship's no. 1 cargo hold and detonates stored ordnance. The resulting explosion nearly shears off the entire fore ship and claims the attacking Avenger in the blast. Aboard, many of the crew and passengers were killed instantly by the shock wave.

The ship sank in within a minute at roughly Lat 7°  22' N, Long 151° 56E into Truk Lagoon. Aboard, captain Nakamaruo, 945 crew, passengers and 400 troops went down with the ship. On March 30, 1944 officially removed from the Navy List and Captain Nakamaruo was posthumously promoted to Rear Admiral.

The Japanese version of the sinking was that "a Grumman crashed near the bridge of the ship and caused a big pillar of fire and black smoke with an explosion. From this explosion, the ship started sinking and went completed under at 0830h". The perception that this Avenger crashed into the ship might be how it was observed from the vantage point of survivors.

During 1969, this shipwreck was first documented by members of Jacques Cousteau's documentary dive team. Footage of this shipwreck appeared in Lagoon of Lost Ships (1969). At that time, the shipwreck was not identified.

Recovery of Remains
In July 1980, divers recovered the remains of approximately 400 individuals from the shipwreck. These remains are cremated during a Shinto ceremony and the ashes returned to Japan.

Today, the forward section of ship disintegrated during the explosion. The interior may be penetrated at great risk due to silt and debris.

Peter Ording adds:
"This was one of my more memorable dives, the engine room photos at a depth of 200' not exactly a routine dive."

Combined Fleet - IJN AIKOKU MARU: Tabular Record of Movement
Lagoon of Lost Ships includes dive footage of this wreck in 1969
Research Notes on Jacques Cousteau's Lagoon of Lost Ships
WWII Wrecks of the Truk Lagoon (2001) pages 266, 270-281 (photos, dive map), 282, 385-386, 415, 501 (index)

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Last Updated
October 19, 2022



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