In February 1940 she helped HMS Imogen and Inglefield to sink the German U-boat U-63 south east of the Shetland Islands and in May she torpedoed and sank the German troop transport Buenos Aires and torpedoed and damaged the troop transport Bahia Castillo.

Möllerthe, Gnom 7, Kobold 1 and Kobold 3; the German minesweeper M 11; German auxiliary submarine chaser UJ D / Treff VIII; the armed trawler V 1109 / Antares and the Swedish cargo ship Haga were all sunk on mines laid by Narwhal.

The auxiliary minesweeper M 1101 / Fock & Hubert and the German cargo ship Palime also struck some of Narwhal's mines.

Alternatively, Narwhal's sister, Porpoise, reported firing upon an unknown submarine, which may account for U-1's loss.

[2] In 2017 a Polish expedition in search of ORP Orzel found a previously unknown wreck which they identified to be most likely HMS Narwhal based on sonar data.