Of all the unreported stories of World War II, none is so haunting and cryptic as the demise of Japan’s battleship Mutsu. A symbol of national pride and naval power at one point, her untimely demise in 1943 raised more questions than answers that persist to this day, turning Mutsu into one of Japan’s most cryptic maritime tragedies.
Mutsu was planned as part of the Imperial Japanese Navy’s grandiose Eight-Eight Fleet Plan—a prewar idea to construct a fleet of eight battleships and eight battlecruisers that would be equal to the world’s greatest naval powers. When this plan was being finalized, Japan laid down the Nagato-class battleships in 1916. Mutsu, the second member of the class, was commissioned in 1920 with a ceremony in attendance of Crown Prince Hirohito and his mother. Partially financed through public contributions, the ship was more than a reflection of military power—it was a question of national dignity. When negotiating the Washington Naval Treaty, Japan fought to save Mutsu, which succeeded where other ships were cut down to size.
Technologically, Mutsu was at the vanguard of her time. Naval historians indicate that the Nagato-class was the world’s first to be equipped with 16-inch guns, marking Japan’s commitment to being the best in naval quality, even if quantity was not an option. During the 1930s, Mutsu and her sister Nagato were renovated to increase armor, propulsion, and added the distinctive pagoda mast. By the start of World War II, she was still a force to be reckoned with, though now overshadowed by the newer Yamato-class super-battleships.
Although large and heavily armed, Mutsu experienced remarkably little action. She served in an auxiliary role in the operations at Pearl Harbor, served as a training vessel, and even towed the Yamato at times. She attended the Battle of Midway but saw no action against enemy ships, and her only combat was at the Battle of the Eastern Solomons, where she shot up American reconnaissance planes. For the majority of the war, Mutsu served more symbolically than tactically—a behemoth ship slowly out of commission for front-line service.
It all changed on June 8, 1943. In Hashirajima Bay, with more than 100 naval cadets and 40 instructors aboard, Mutsu experienced a massive explosion under her No. 3 turret at exactly 12:13 p.m. The explosion was so massive that it cleaved the ship in two. The forward half sank instantly, while the rear end caught fire and drifted before eventually sinking hours later. Of the 1,474 people on board, 353 survived, among them only 13 cadets. The magnitude of the tragedy stunned the Imperial Navy and the country.
In its wake, panic and concealment set in. Anti-submarine warnings were sounded, though no foe was discovered. The catastrophe was kept secret to preserve morale. Survivors were transferred discreetly, and families remained ignorant for months. A case in point: the widow of Captain Teruhiko Miyoshi of Mutsu did not discover her husband was dead until January 1944, some seven months later.
The nature of the explosion is still controversial. Initial rumor centered on the highly explosive Type 3 “Sanshikidan” shells stored in the immediate vicinity. Onlookers described the smoke as red and brown rather than the expected coloring for such ammunition.
Ultimately, the Navy deemed that sabotage was the cause, blaming a seaman who was to face a court-martial that day. Most found this alleged explanation dubious, pointing out that no body was discovered among the initial salvage efforts, prompting speculation that he had been made a convenient scapegoat.
Other theories point to internal failure. Mutsu had enormous quantities of combustible material on board, and her old electrical system perhaps ignited a blaze that spread to the magazine. Such a failure would have been embarrassing for a navy that was already having trouble keeping a presence in the Pacific.
Salvage operations persisted well after the war, with fragments of Mutsu, such as a turret and her crest, ultimately retrieved. In a strange irony, the remains of the missing sailor were discovered in 1970, but the core question remained unanswered.
Now, the Mutsu Memorial Museum is a memorial to the dead, a reminder of the way pride and ambition can become disastrous, and of the flesh and blood cost of the steel and flames of sea warfare. Was Mutsu sunk through sabotage, accident, or an unfixed secret flaw that had existed for too long? It may never be known, but her tale remains one of the most poignant pages in the history of Japan’s navy.