Apparently the still unexplained sinking of the Mutsu is well known in certain naval history circles, but I hadn’t heard of it previously so I post it for other members’ information. Hashirajima, in the region of the naval base at Kure, was the home base of the anchored Combined Fleet, and indeed some of the main ships in that Fleet spent a lot of the war anchored there.
8 June 1943:
MUTSU is moored at the flagship buoy midway between Hashirajima and the Suo-Oshima islands about two miles SW of Hashirajima. She hosts 113 flying cadets and 40 instructors of the Tsuchiura Naval Air Group who are aboard for a familiarization tour.Captain Tsuruoka’s FUSO is moored about 1,100 yards SW of MUTSU. DesRon 11’s flagship, light cruiser TATSUTA and several of the squadron’s newly commissioned destroyers are moored more distantly south of Hashirajima.
1145: After lunch, MUTSU’s deck crew prepares to move to mooring buoy No. 2 because NAGATO is expected to return at about 1300 from Kure after being drydocked. There is heavy fog and visibility is down to 500 yards. MUTSU’s magazines contain a full load of ammunition including 16.1-inch Type 3 “Sanshikidan” incendiary shells designed as anti-aircraft rounds. Each shell weighs 2,064-lbs. and contains 1,200 submunitions. Each turret magazine contains 240 shells (120 per gun), including 50 “sanshiki-dans.”
1213: Suddenly, MUTSU’s No. 3 turret’s magazine explodes. Vice Admiral Shimizu, Commander of the First Fleet, a few miles away aboard NAGATO sees a brilliant white explosion. Shortly thereafter, he receives a coded message from FUSO’s Captain Tsuruoka. It says: “MUTSU blew up!”
MUTSU breaks in two. The 535-ft forward section collapses to starboard, sinks quickly and lies on the pagoda mast on the floor of the bay. The 147-ft stern section upends, but remains floating. FUSO immediately launches two of her Vedette boats. Her crew rescues 353 survivors of the 1,474 crewmembers aboard MUTSU. Only 13 of the visiting flying cadets/instructors are among the survivors. The IJN can ill-afford the loss of 140 instructors and pilot trainees, particularly after the heavy losses sustained in April in Operation “I-GO” during the reinforcement of the 11th Air Fleet at Rabaul. Later, destroyers TAMANAMI and WAKATSUKI arrive, as do boats from TATSUTA and the cruiser MOGAMI. An antisubmarine alert is put into effect immediately.
1430: NAGATO arrives after zigzagging through Hiroshima Bay. Later, since no submarines are sighted, the alert is cancelled. Later, the frequency of patrols by naval vessels and aircraft is increased in Hiroshima Bay, the Iyo-nada and the Bungo and Kii Suido channels. NAGATO moors about 3,000 yards off FUSO’s port beam and takes aboard the survivors rescued by TATSUTA. All 39 wounded sailors are transported by TAMANAMI to a secluded hospital on Mitsukoshima. [1] A major cover-up is launched to conceal that something has happened to MUTSU. To further prevent rumors from spreading, many survivors are later sent to remote garrisons on Tarawa, Makin, Kwajalein, Saipan and Truk.
9 June 1943:
Hashirajima: At about 0200, MUTSU’s stern section sinks and comes to rest nearly upright in 130 feet of water in Hiroshima Bay at 33-58N, 132-24E.In the morning, the first divers arrive and remain on the site for several months. FUSO serves as the “headquarters” for the salvage efforts. To conceal that MUTSU has sunk the divers are told that the ship they are exploring is similar to sister-ship NAGATO. Then the divers are allowed to familiarize themselves on NAGATO.
The final list of those lost aboard MUTSU totals 1,121 men including her skipper, Captain Miyoshi and his Executive Officer, Captain Ono Koro (former XO of KIRISHIMA), both of whom are promoted to Rear Admiral, posthumously.
Tokyo: The IJN suspects that the Type 3"Sanshiki-dan" incendiaries are the cause because a fire at the Sagami arsenal a few years earlier was caused by improper storage of the incendiary materials. After the accident, the Minister of the Navy, Admiral Shimada Shigetaro (former CO of HIEI) orders the Type 3 shells offloaded from all IJN ships carrying them.
Hashirajima: The “M-Commission” led by 60-year old Admiral Shiozawa Koichi (former CO of FURATAKA) is convened to conduct a formal accident investigation. Shiozawa considers all possibilities from the possibile detonation of “Sanshiki” shells to improbable attacks by a lone American torpedo plane or an attack by either a midget or fleet submarine.
Cdr Yasui Yasukado, the inventor of the “Sanshiki” shells is called in to testify. Tests are conducted at Kamegakubi on some shells salvaged from turret No. 3 and on shells from the previous lot and the next lot. An experiment is conducted by engineer troops with dozens of witnesses of the accident who had survived. The test uses a specially built model of turret No. 3. The final experiment is also based on the identification of the color of the smoke generated during the burning of Sanshiki shells compared to gunpowder. The smoke of burning powder is reddish-brown, while the smoke of burning Sanshiki shells is white. The witnesses of the disaster insist that they saw reddish-brown smoke. Moreover, during testing, it becomes clear that explosions do not occur below 80 degrees Centigrade. Cdr Yasui only escapes blame for the disaster by the IJN’s top brass because the tests disclose that the Type 3 shells do not explode easily.
The M-Commission labors for two months and prepares their report. The commission doubts that the shells had caused the disaster. As a result the loading of Sanshiki shells on board ships is resumed. Later, the IJN revises completely their standards for the handling and storage of explosives aboard ships.
The investigation concludes that the explosion was “most likely caused by human interference”. Some investigators think there was a ring of saboteurs, but the principal suspect is a disgruntled seaman gunner of turret No. 3 who had brooded over theft charges and was killed in the blast. The divers search for his body but it is never found. During the war, the belief persists that, somehow, he managed to escape.
22 July 1943:
Although the divers report that MUTSU is “bent like a broken nail”, it is proposed to salvage the ship, tow it to a drydock at Kure and put her back on the line - optimistically - in three months. To convince their superiors in Kure, a dive is made with a modified 6-man minisub, but it snags on a railing on MUTSU. All officers aboard almost suffocate before the minisub breaks free. Finally, it is decided that it is impossible to raise MUTSU.15 August 1943:
The survivors of MUTSU stationed on FUSO are transferred to NAGATO that, with other fleet units, departs via Yashima and Yokosuka for Truk. Once the survivors arrive on Truk, they form the reserve unit of the local 41st Guard Force. About 150 are sent to Saipan and almost all are killed there in 1944 during the U. S. invasion of the Marianas.1 September 1943:
Removed from the Navy List.Doubts as to the cause of the disaster remain, especially by those who favor the explanation that a submarine attacked MUTSU. Several months later IJN officials question the German naval attaché in Tokyo, Vice Admiral (later Admiral/Knight’s Cross) Paul Wenneker (former CO of Panzerschiff DEUTSCHLAND/LUTZOW), about the circumstances surrounding British Operation “Source.” Only after completing the exploration of MUTSU’s wreck, do the Japanese decide that, indeed, the explosion must have occurred from within the magazine itself. [2]
July 1944:
The oiled-starved IJN cut a hole in the bottom of MUTSU’s hulk and pump out 580-tons of fuel oil for use by their ships in Operation Take (“Bamboo”).31 July 1945:
Seletar Naval Base, Singapore. Cruiser TAKAO is attacked and damaged heavily by British X-craft. For some, doubts return about the cause of the loss of MUTSU.
http://www.combinedfleet.com/Mutsu.html
Mutsu
Country Japan
Ship Class Nagato-class Battleship
Builder Yokosuka Naval Arsenal, Japan
Laid Down 1 June 1918
Launched 31 May 1920
Commissioned 24 October 1921
Sunk 6 June 1943
Displacement 39050 tons standard; 42850 tons full
Length 725 feet
Beam 113 feet
Draft 31 feet
Machinery Four Kampon oil-fired boilers and six small boilers, geared turbines, 4 shafts
Power Output 80000 SHP
Speed 27 knots
Range 5,500nm at 16 knots
Crew 1368
Armament 8x410mm guns, 18x140mm guns, 8x127mm AA guns, 98x25mm AA guns
Aircraft 3
http://ww2db.com/ship_spec.php?ship_id=B27