[9] Spot waited for an hour and then sent over a boarding party of seven men to plant demolition charges and search for intelligence material.

Spot was surfaced and heading for deeper water but could not elude one of the escorts, the minesweeper W-17, which closed to 4,200 yards (3,800 m) and opened fire.

The escort dropped a few depth charge patterns which caused no damage, and the submarine returned to Saipan on 23 March to reload.

On 31 March 1945, she was on the surface in the Philippine Sea 425 nautical miles (787 km; 489 mi) southeast of Kagoshima, Kyushu, Japan at 29°14′N 137°18′E / 29.233°N 137.300°E / 29.233; 137.300 when she sighted a destroyer that offered no recognition signals.

After Spot reached a depth of 450 feet (137 m), she and the destroyer exchanged recognition signals and the destrover discontinued its attack.

After aircraft from the Fast Carrier Task Force sank battleship Yamato, a cruiser, and four destroyers in the East China Sea on 7 April, the submarine patrolled in that area.

She hunted off the China coast and then conducted a reconnaissance of Kokuzan To, off Korea and decided to shell a radio station on the northwest tip of the island.

On the evening of 25 April, she surfaced and began the bombardment which hit an oil storage area, several barracks, and set the radio station on fire.

She then patrolled in the East China and Yellow Seas, sinking two junks by gunfire before returning to Saipan on 18 July.

She sailed for San Diego on 27 August and provided services for antisubmarine warfare units there from 3 September 1945 to 2 March 1946.

A streamlined sail was added but, unusually for a post-World War II submarine, her deck gun was retained.

In 1980, Simpson was used extensively by director Kinji Fukasaku in the disaster film Fukkatsu no hi (titled in EnglishVirus and Day of Resurrection).