After fitting out, Seawolf departed Portsmouth, New Hampshire on 12 April 1940 for her shakedown cruise, which lasted until 21 June and took her as far south as the Panama Canal Zone.

She loaded 30–40 tons of .50 cal (12.7 mm) antiaircraft ammunition for use by American forces on Corregidor and sailed for Manila Bay on 16 January.

The submarine sighted seven Japanese freighters accompanied by four destroyers and a cruiser on 21 January, but had no opportunity to fire any of the eight torpedoes that she had aboard.

[6] Seawolf sailed out of Surabaya on 15 February and began patrolling in the Java Sea-Lombok Strait area.

On 1 April, she stealthily approached the anchorage at Christmas Island where the Japanese invasion force lay at anchor.

Though Seawolf was credited with a sinking at the time,[7] only one torpedo hit, causing significant damage to the ship, although not harming any of the crew.

Seawolf arrived at Mare Island Naval Shipyard on 10 December 1942 and underwent an overhaul[11] that lasted until 24 February 1943.

Seawolf returned to Hunters Point Naval Shipyard for refitting and departed that island on 17 May and headed for the East China Sea.

The submarine tracked a convoy of 11 ships and fired a spread of torpedoes at a large freighter on 6 June.

The submarine refitted at Pearl Harbor, and on 22 December 1943, headed for the East China Sea on what was to be her most lucrative patrol.

On 14 January, Seawolf fired her last four torpedoes at two merchant ships in a convoy, damaging one and sinking Yamatsuru Maru.

The submarine approached to within 700 yards (640 m) of the beach, offloaded supplies and men, picked up a Captain Frank Young, an Allied Intelligence Bureau coast watcher, and took him to Brisbane.

The operation order also called for Seawolf to land a party and their supplies on northern Palawan Island.

She reached Manus Island on 29 September, refueled, and sailed the same day carrying stores and Army personnel to the east coast of Samar.

The destroyer escort Shelton was torpedoed and sunk, and Richard M. Rowell began to search for the enemy.

Rowell's commanding officer knew he was in a safety lane,[13] but, having failed to get word Seawolf was behind schedule,[14] believed there was no U.S. submarine nearby and chose to attack.

Post-war examination of Japanese records shows no attack listed that could account for the loss of Seawolf.

While it is possible Seawolf was lost to an operational casualty or as a result of an unrecorded enemy attack, it is more likely she was sunk by friendly fire.

Kopp was en route to an undisclosed location in the Philippines to conduct a clandestine mission in support of the upcoming Allied landing on Leyte.