The submarine Narwhal gave her name to her class. She was laid down at Portsmouth Navy Yard on 10 May 1927 and commissioned on 17 December 1929. She displaced 2,730 tons and was 371 feet in length overall and 34 feet in the beam. She carried two 6-inch and four 20mm Oerlikon guns and had ten 21-inch torpedo tubes. She was completed on 21 July 1930. On 7 December 1941 she was moored next to Gudgeon in South-East Loch.