She cleared Pearl Harbor 7 September for her first war patrol, taking station off the Palau Islands. Muskallunge carried the first electric torpedoes to be fired in the war by an American submarine. She made two attacks on Japanese convoys; although handicapped by malfunctioning torpedoes, she managed to damage a passenger freighter and a cargo ship. On 25 October Muskallunge returned to Pearl Harbor.
She sailed 27 November for her second war patrol, which was conducted in the western Carolines area and south of Guam. During this patrol Muskallunge scored hits on a tanker and two freighters, sinking one of the Noroto Maru class, before returning to Pearl Harbor 21 January 1944. From there, she went to the West Coast for overhaul.
Third, fourth, and fifth war patrols, April – December 1944
After overhaul at Mare Island early in the year, Muskallunge left Pearl Harbor 30 April on her third war patrol. In June she joined eight other submarines in an operation designed to intercept any enemy forces approaching the Marianas which the Navy was invading. In the ensuing Battle of the Philippine Sea two of these submarines landed fatal blows on Japanese carriers and American naval aircraft wiped out the Japanese Fleet's air arm in a one-sided melee known as "the Marianas Turkey Shoot." Muskallunge ended the patrol at Fremantle, Australia, 4 July.
In company with Flier, Muskallunge got underway 1 August for the South China Sea on her fourth war patrol. On 21 August off French Indochina she sank 7,163-ton passenger-cargo Durban Maru before being severely depth charged. The submarine docked in Fremantle 22 September for refit.
Her fifth war patrol, 19 October to 14 December, saw her operating west of Palawan Passage. She then left Pearl Harbor 16 December for overhaul at Mare Island Navy Yard, returning 9 April 1945.
Sixth and seventh war patrols, April – August 1945
On 26 April Muskallunge departed Pearl Harbor for patrol off Formosa. She also acted as lifeguard for Philippine-based airstrikes on China and Formosa on her sixth war patrol. She sailed to Midway Atoll via Saipan to complete the patrol on arrival 15 June.
Her seventh and last war patrol started 30 July when Muskallunge got underway for the Kurile Islands, north of Japan. On 8 August she attacked several small ships through dense fog. Her guns damaged two of the Japanese ships, but enemy fire killed one of the submarine's gunners and wounded two other bluejackets. The news of victory brought orders to Tokyo Bay for the surrender ceremonies on board the battleshipMissouri 2 September. The next day Muskallunge sailed for New London via Pearl Harbor and the Panama Canal. After operations with the Atlantic Fleet, she decommissioned and joined the Atlantic Reserve Fleet there 29 January 1947.
Muskallunge recommissioned 31 August 1956 prior to transfer to Brazil; decommissioned 18 January 1957, and the same day was loaned under the Military Assistance Program. She served the Brazilian Navy as Humaitá (S14) until returned to the United States in March 1968 and sunk as a target off Long Island, NY on 9 July 1968.
Discovery
On 26 June 2021 NOAAS Okeanos Explorer explored the wreckage of Muskallunge with the ROV Deep Discoverer. The hull was found to have been severed near the forward engine room with the bow and stern falling to the sea floor separately.
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^ abcdefBauer, K. Jack; Roberts, Stephen S. (1991). Register of Ships of the U.S. Navy, 1775-1990: Major Combatants. Westport, Connecticut: Greenwood Press. pp. 271–273. ISBN0-313-26202-0.