Akitsushima (秋津洲) was a seaplane tender of the Imperial Japanese Navy during World War Two. Her name translates to “Dragonfly Island”, an ancient name for Japan. She had a length of 376 feet 8 inches (114.8 m) and a beam of 51 feet 10 inches (15.8 m) with a displacement of 5,000 tons. Four Kampon 8,000 HP (6,000 Kw) diesels provided propulsion. She was well armed for an auxiliary with two twin Type 89 127mm mounts, two twin 25mm cannon, and depth charges for anti-submarine defense.
The IJN operated two types of large four-engine long range flying boats during the Pacific War, the H6K “Mavis” and the H8K “Emily”. The purpose of the Akitsushima was to provide a logistical base for these flying boats where the aircraft could be serviced and to house and feed their crews. She carried enough supplies and provisions on board to support combat operations for a detachment of eight flying boats for two weeks. A Japanese wartime newsreel showing Mavis and Emily operations here: https://www.youtube.com/watch?v=bygNXMe1dY4
The ship was not intended to launch aircraft herself. Akitsushima was to anchor in a protected harbor and the aircraft were to fly in to join her. The aircraft would moor to buoys in the harbor, then they would be serviced and crews transferred using the ship’s boats. If repairs or maintenance was required, the large crane on the fantail could hoist the aircraft aboard. The aircraft was positioned on a cradle and could be rotated on a turntable as needed.
Akitsushima was commissioned on 29APR42 and shortly thereafter sailed for the Japanese base at Rabaul, New Guinea. She spent the rest of the year supporting operations in the South Pacific, moving between Buka, Rabaul, Kavieng, and the Shortlands. She was subjected to aerial bombardment on several occasions but did not suffer any significant damage. In December she sailed for Yokosuka, returning again to Kavieng in JAN43.
On 23JAN43 USS Guardfish (SS 217) torpedoed and sank the Japanese destroyer Hakaze which was escorting Akitsushima at the time. Akitsushima reacted quickly and was able to save the majority of the crew. She spent the next several months on operations, returning to Japan for drydocking at Yokohama in November.
On 17FEB44 she was at Truk Lagoon when the anchorage was raided by carrier aircraft and surface ships from TF 58 during Operation Hailstone. She received two bomb hits on the 17th and a third on the 18th. Akitsushima suffered severe damage but remained afloat, forcing her return to drydock in Yokosuka for repairs. Japanese losses were heavy, losing 40 ships and 250 aircraft. One of the casualties was the 10,000 ton repair ship Akashi. This left the Imperial Navy lacking in deployable repair capability so it was decided to add workshops to Akitsushima during her repairs. It is likely that her search radar and additional anti-aircraft weapons were also added at this time, bringing her total to four triple, two twin, and three single 25mm AA. She was to remain in Japanese waters for most of the summer, sailing for the Philippines in September.
On 24SEP44 she was anchored at Coron, Philippines along with several other Japanese vessels when US Navy carrier aircraft from TF 38 raided the anchorage. Akitsushima was not so lucky this time. She was hit by three bombs which blew out much of her plating under the aircraft cradle. She quickly rolled onto her side and sank. The majority of her crew was rescued or swam to shore. Akitsushima lies on her port side at a depth of 108 feet (33 meters) and is a popular destination for wreck divers.