Her first report, made as she patrolled north of Kiska Island, stated she had been attacked by a Japanese destroyer and had fired Mark 14 torpedoes at her with inconclusive results.

Captured Japanese records show no antisubmarine attacks in the Kiska area, and the fate of Grunion remained a mystery for 65 years, until the discovery in the Bering Sea in August 2007 of a wreck believed to be her.

[9] In 1998 Lieutenant Colonel Richard Lane purchased for $1 a wiring diagram from a Japanese cargo ship, Kano Maru, which had been active during World War II.

[3] Several years later, John Abele, cofounder of Boston Scientific, met Dr. Robert Ballard, famous for discovering the wreck of the RMS Titanic.

[3] In 2007, using a remotely operated underwater vehicle (ROV), DSSI/Oceaneering, returned to the site and took video recordings of the imploded remains of a submarine, which had markings in English, and propeller guards and limber holes identical to those of Grunion.

[3] The damage the torpedo inflicted, combined with a jammed rear dive plane, triggered a sequence of events that caused the loss of depth control.

The wreckage then slid two-thirds of a nautical mile (0.77 mi; 1.2 km) down the side of an extinct volcano, coming to rest on a notch in the underwater mountain.

[3] In 2019, the missing bow section was located one-quarter of a nautical mile (0.29 mi; 0.46 km) from the rest of the submarine on a slope of an underwater volcano at a depth of over 2,000 feet (610 m).