Jack Pancoast was born on November 25, 1918, in Lincoln Place, Pennsylvania. He enlisted in the U.S. Navy on March 25, 1936, and completed basic training and advanced training at NTS Newport, Rhode Island, in July 1936. His first assignment was aboard the cruiser USS Indianapolis (CA-35) from July 1936 to January 1938, followed by service aboard the destroyer USS Henley (DD-391) from January 1938 to April 1939. MM2c Pancoast served aboard the submarine USS S-41 (SS-146) from June 1939 to September 1941, and then at San Francisco, California, before joining the crew of the submarine USS Grunion (SS-216) during her fitting out in January 1942. He remained aboard the Grunion through her commissioning in April 1942, and was killed in action during a confrontation with the armed Japanese freighter Kano Maru on July 30, 1942. On August 22, 2007, a search team organized by the three sons of CDR Mannert Abele (the Captain of the Grunion when she was sunk) used a remotely operated vehicle to find a sunken vessel 3,000 feet down in the Bering Sea north of Kiska Island at the tip of the Aleutian Islands. On October 1, 2008, the U.S. Navy announced that the sunken vessel is the World War II submarine USS Grunion (SS-216).

His Navy Commendation Medal Citation reads:

For meritorious conduct as a member of the crew of the U.S.S. GRUNION which destroyed three enemy destroyers while engaged in a war patrol in enemy controlled waters. Despite severe and persistent anti-submarine measures resulting from these three successful attacks, the GRUNION was brought safely through the counter attacks and continued an aggressive war patrol. As a member of the crew of the GRUNION, your performance of duty was an important and material contribution to the prosecution of this war.