The Unkai Maru was a 331ft/100m, 3,100-ton Cargo ship built in Great Britain in 1905 by William Grey and Co. Originally named ‘Venus’ she was bought by Nakamura Gumi Ltd in 1911, along with 5 similar vessels and renamed ‘Unkai Maru No. 6’. The word ‘Maru’ designates a merchant vessel.
This relatively old coal fired steam ship was requisitioned by the Japanese Navy late in the war, on January 5th 1944, and she was sent from Tokyo to Yokosuka and then onto Truk, arriving there on 30th January 1944.
The Unkai Maru was attacked on the first day of Operation Hailstone initially by planes from USS Essex. After being hit on the port side and port quarter she was seen to be listing to starboard. Later that day she was attacked by planes from USS Bunker Hill and USS Yorktown. A 1000lb bomb from a Yorktown plane hit amidships causing a large fire to breakout. This fire was still burning the next morning when planes from the Essex scored hits around the bow, lifting it out of the water. Still afloat when the planes left, Japanese reports indicate she sank shortly afterwards. Three crewmen died during these attacks.
The Unkai Maru is the oldest ship in Truk Lagoon and she rests upright on an even keel close to the N tip of Uman Island at 130ft/40m. The deck is at 100ft/30m while the superstructure comes up to 80ft/25m. The 3 inch bow gun still has the builder’s plate, and there are many lantern pieces scattered around the foredeck. The holds are empty, except for Hold 1, which contains many personal items including boots, drinking flasks, bottles, gas masks and china (with the 5 point star of the Japanese Infantry).
The bridge area was destroyed by raging fires; the funnel is fallen and lies on the deck. The engine room has a steering engine located aft; with chains and rods that connect along the aft deck to an old type steering mechanism up on the poop deck, and there are depth charges at the stern.