Mutsu Memorial Museum

The Mutsu Memorial Museum (陸奥記念館) is located in the Nagisa Park complex on Suo-Oshima (周防大島), the third-largest island in the Seto Inland Sea, in Oshima District, Yamaguchi Prefecture. The museum commemorates the Imperial Japanese Navy battleship Mutsu and the 1,121 men who perished in her catastrophic loss.

The battleship Mutsu was the second vessel of the Nagato class, Japan's first class of super-dreadnoughts armed with 41 cm (16.1-inch) guns — the most powerful naval guns in the world at the time of her completion. Laid down at Yokosuka Naval Arsenal on June 1, 1918, launched on May 31, 1920, and commissioned on October 24, 1921, Mutsu displaced 32,720 tonnes standard and 39,116 tonnes at full load. Her main armament consisted of eight 41 cm guns in four twin turrets. She served through the interwar period and underwent a major reconstruction in the 1930s that added torpedo bulges, upgraded her propulsion, and increased her anti-aircraft armament.

On June 8, 1943, Mutsu was moored at the Hashirajima fleet anchorage in Hiroshima Bay — the Combined Fleet's main wartime base. In addition to her regular crew, 113 flying cadets and 40 instructors from the Tsuchiura Naval Air Group were aboard for familiarization training. At 12:13, the magazine of her No. 3 turret detonated in a massive explosion that broke the ship in two. The forward section capsized to starboard and sank almost immediately. Nearby vessels including battleship Fuso, destroyers Tamanami and Wakatsuki, and cruisers Tatsuta and Mogami launched rescue operations, but only 353 of the 1,474 personnel aboard survived. It was the Imperial Japanese Navy's worst single-ship disaster in terms of displacement and casualties.

An investigation committee chaired by Admiral Shiozawa Koichi concluded the explosion originated in the No. 3 turret's powder magazine. Investigators initially suspected the Type 3 anti-aircraft shrapnel shell (containing white phosphorus-filled steel tubes) had self-ignited, but experimental testing failed to replicate this. The true cause was never definitively established, though suspicion fell on either arson by a disgruntled crew member or propellant decomposition. The IJN dispersed the survivors to various postings and suppressed news of the sinking to maintain morale.

Salvage operations began after the war. Between 1970 and 1978, the Fukada Salvage Company raised significant portions of the wreck, including a 36-metre bow section, propellers, rudder, anchors, the main mast, guns, and thousands of personal artifacts. The salvaged bow section and other large items are displayed outdoors at the museum.

The original museum was completed in November 1972 by the then town of Tōwa (some English-language sources give July 1970), near the site on Suo-Oshima from which the explosion could be observed. In April 1994, the museum relocated to its current purpose-built facility within the Nagisa Park complex to make way for a new road. Since 1963, a memorial ceremony has been held every June 8 to honor the fallen crew. The museum grounds also display a Shin Meiwa PS-1 anti-submarine flying boat (aircraft #5815).

Exhibits include salvaged ship components — hull plating, portholes, valves, shell casings — as well as crew personal effects, photographs, a detailed model of the battleship, and panels documenting the ship's construction, service history, the disaster, investigation, and postwar salvage. The museum offers a poignant view across the Seto Inland Sea toward the approximate location where Mutsu sank.