in 1944 during the battle for the island. At the time of the explosion, Mutsus magazine contained some 16-inch Type 3 "Sanshikidan" incendiary shrapnel anti-aircraft shells, which had 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 the investigation into the loss. Investigation into the loss A commission led by Admiral Kōichi Shiozawa was convened three days after the sinking to investigate the loss. The commission considered several possible causes: Sabotage by enemy secret agents. Given the heavy security at the anchorage and lack of claims of responsibility by the Allies, this could be discounted. Sabotage by a disgruntled crewman. While no individual was named in the commission's final report, its conclusion was that the cause of the explosion was most likely a crewman in No. 3 turret who had recently been accused of theft and was believed to be suicidal. A midget or fleet submarine attack. Extensive searches immediately following the sinking had failed to detect any enemy submarine, and the Allies had made no attempt at claiming the enormous propaganda value of sinking a capital ship in her home anchorage; consequently, this possibility was quickly discounted. Eyewitnesses also spoke of a reddish-brown fireball, which indicated a magazine explosion; this was confirmed during exploration of the wreck by divers. Accidental explosion within a magazine. While the Mutsu carried many projectiles, immediate suspicion focused on the Type 3 anti-aircraft shell as it was believed to have caused a fire before the war at the Sagami arsenal. Known as "sanshiki-dan" (Japanese for "type 3 shell"), these were fired by the main armament and contained 900 to 1,200 25 mm diameter steel tubes (depending upon sources), each containing an incendiary charge. Tests were conducted at Kamegakubi Naval Proving Ground on several shells salvaged from No. 3 turret and on shells from the previous and succeeding manufacturing batches. Using a specially built model of the Mutsus No. 3 turret, the experiments were unable to induce the shells to explode under normal conditions. The commission issued its preliminary conclusions on 25 June, well before the divers had completed their investigation of the wreck, and concluded that the explosion was the result of a