Battleship Mutsu Explosion

On Tuesday 8 June 1943 the Mutsu was moored at the Battleship Division 2 flagship buoy No.2 in the Hashirajima fleet anchorage approximately 3 km south-west of the island of Hashirajima and just to the west of Mitsuhima island in the Inland Sea, hosting 113 flying cadets and 40 instructors from the Tsuchiura Naval Air Group on a familiarization tour. Suddenly at 1213 the magazine of her No. 3 turret exploded. The explosion was so severe that it instantly sheared the stern from the ship forward of turret 3, causing major flooding in the boiler rooms and main engine room. The 535-foot (163 m) front section of the ship rolled to starboard and sank almost immediately. The stern section upended and remained floating until about 0200 hours on 9 June 1943 before sinking, coming to rest just a few hundred feet south of the main wreck.

The battleship Fuso immediately launched two boats which, together with assistance from the destroyers Tamanuani, Wakatsuki, cruisers Tatsuta and Mogami, were able to rescue 353 survivors from the 1,474 crew members and visitors aboard Mutsu, resulting in a loss of 1,121. Only 13 of the visiting flying cadets/instructors were among the survivors. During the initial and later salvage operations, lasting until 1978, all but 272 of the bodies were recovered. Every year on the 8 June, a memorial service is held for the crew at a memorial raised to their honour in 1963 in Tôwa Chô.

After the explosion, as the rescue operations commenced, the fleet was mobilized and the area was combed for Allied submarines and X-craft, but no traces were found.

To avert the potential damage to morale of the loss of a battleship coming so soon after the string of recent setbacks in the war effort, the Mutsu's loss was declared a state secret. Mass cremations of recovered bodies commenced almost immediately after the sinking. While Captain Miyoshi's body was recovered from his cabin by divers on 17 June, his wife was not officially notified until 6 January 1944, how he had died was not mentioned. Both he and his second in command, Captain Ono Koro, were posthumously promoted to Rear Admiral, which was normal Japanese Navy practice.

The 39 wounded survivors were sent to a secluded hospital on Mitsukoshima.

To further prevent rumours from spreading, healthy and recovered survivors were re-assigned to various garrisons in the Pacific Ocean. Some of the survivors were sent to Truk in the Caroline Islands to form the 41st Guard Force. Another 150 were sent to Saipan in the Mariana Islands where most were killed in 1944 during the Battle of Saipan.

At the time of the explosion the Mutsu's magazine contained a number of 16-inch Type 3 "Sanshikidan" incendiary shells, which had previously caused a fire at the Sagami arsenal several years earlier due to improper storage. Because they might have been the cause of the explosion, the Minister of the Navy, Admiral Shimada Shigetaro, immediately ordered the removal of Type 3 shells from all IJN ships carrying them, until the conclusion of investigations into the loss.

Around noontime on June 8, 1943, while moored in Hiroshima Bay, Mutsu was suddenly rocked by a violent explosion, which blew the ship in two. The 535-foot forward section rolls over to starboard and sinks immediately, coming to rest upside down in 130 feet of water. The 147-foot aft section upends, and remains floating with the stern pointing up towards the sky. It finally sank 14 hours later at 33-58N, 132-24E, and no doubt many lives were saved by this delay in sinking. Boats from other ships came to the aid of the survivors, rescuing 353 crew members, while 1,121 men lost their lives.