On 11 November 1944 B-29 air strikes against Tokyo were cancelled and Archerfish, originally assigned to lifesaving duties, was free to patrol the waters near Tokyo Bay. On the night of 28 November she spots what is believed to be a tanker leaving the bay. Lookouts later determine that it’s a large aircraft carrier with three destroyer escorts.
Archerfish CO, CDR Joseph F. Enright, begins a six-hour surface track on the carrier in anticipation of a submerged attack. When the carrier turned into the sub’s path six torpedos were fired. They were set for shallow running in order to increase the chances of a hit in case they ran deeper than set. Two torpedo hits were seen and four more were heard. The carrier sank in 5 hours.
Enright believed the target to be, and was credited for, a Hayataka-class carrier weighing 28,000 tons. Post war accounting identified the target as the Shinano, a 72,000 ton supercarrier, originally laid down as a Yamato-class battleship, the first of its kind. It was so secret it was being transferred from Yokusuka to Kure for final fitting out. One of the items on the list for installation were her watertight doors. Once the torpedos hit, the inexperienced crew could do nothing to save her. As of 2014, Shinano remains the the largest warship ever sunk buy a submarine. Archerfish earned the Presidential Unit Citation for this patrol.