The configuration of V-4, V-5, and V-6 resulted from an evolving strategic concept that increasingly emphasized the possibility of a naval war with Japan in the far western Pacific.

[1]: 259  The auxiliary engines were for charging batteries or for increased surface speed via a diesel-electric system providing power to the main electric motors.

Welding was used to join the vertical keel plates, and also in other non-critical areas like the superstructure, piping brackets, and support framing.

She trained in New England waters until 31 January 1931, when she sailed for the West Coast via the Panama Canal, arriving San Diego on 4 April.

Within minutes of the first enemy bomb explosions on Ford Island, Narwhal's gunners were in action to assist in the destruction of two torpedo planes.

Her aging BuEng MAN engines were replaced at this time with four GM-Winton 16-278As and other upgraded machinery, including more powerful electric motors and new batteries.

The night of 15 July, Narwhal drew so much enemy attention to her presence she was forced to dive from the shells, but she accomplished her mission: the other submarines slipped through Etorofu Strait without detection.

Upon arrival, Narwhal prepared to participate in the campaign to assist the guerrilla movement in the Philippines begun in January 1943, when Gudgeon disembarked six Filipinos and a ton of equipment on Negros Island.

Narwhal eventually became the leading submarine in supporting the Philippine guerrilla movement with nine secret transport missions to her credit.

Narwhal was loaded down with 92 short tons (83 t) of ammunition and stores and a party of ten for her seventh patrol, from 23 October – 22 November, supporting Philippine guerrillas.

She was in the Sulu Sea, off Mindanao, the night of 10 November en route to Puluan Bay when two Japanese ships astern opened fire.

The night of 13 November, she entered Ptiluan Bay stealthily to disembark her passengers and half of her cargo while lying off the starboard side of Dona Jitana Maru.

By midnight Narwhal was safely on her way to Nasipit, on Mindanao, where she docked on 15 November to unload the rest of her stores to the tune of "Anchors Aweigh" played by a grateful Filipino band.

On her ninth war patrol – from 18 January to 15 February 1944 – the submarine returned to Darwin to embark observer Commander F. Kent Loomis and more stores.

Following a nighttime transit of the Surigao Strait, Narwhal slipped west and north, made a submerged patrol off Naso Point, Panay, then headed for Pandan Bay to transfer cargo to sailing craft.

That evening, she damaged Karatsu (the captured USS Luzon (PR-7)) and was heavily bombarded with depth charges by enemy escorts for her trouble.

On the night of 30 August, Narwhal surfaced in Dibut Bay on the east coast of Luzon for her usual disembarking procedures, greatly speeded this time by the use of bamboo rafts built by the shore party under the direction of Major Robert Lapham and Lieutenant Commander Charles "Chick" Parsons, a liaison man in the Philippine supply and evacuation missions.

Before midnight on 2 September, Narwhal sent a party and supplies ashore to a beach off the mouth of the Masanga River, and received four evacuees in return to complete the patrol.

Forced to blow her main ballast to stop the steep dive, Narwhal reversed direction and popped out of the water stern first just two minutes after she went down.

Narwhal departed Brisbane on 6 January 1945 for the east coast via the Panama Canal, entering the Philadelphia Navy Yard on 21 February, where she was decommissioned on 23 April.

The town of Nasipit in Agusan del Norte, created a memorial in commemoration of the USS Narwhal's efforts during World War II.

[16][17][4]: 775 The opening of the movie Operation Pacific may have been inspired by the Narwhal's seventh war patrol, where 32 civilians, including 8 children and a baby, were evacuated to Australia.