On 8 June 1943, "Mutsu" was moored in the Hashirajima fleet anchorage, with 113 flying cadets and 40 instructors from the Tsuchiura Naval Air Group aboard for familiarisation. At 12:13 the magazine of her No. 3 turret exploded, destroying the adjacent structure of the ship and cutting her in two. A massive influx of water into the machinery spaces caused the forward section of the ship to capsize to starboard and sink almost immediately. The stern section upended and remained floating until about 02:00 hours on 9 June before sinking, coming to rest a few hundred feet south of the main wreck at coordinates .