The Porpoise class was the first class of operational submarines built for the Royal Navy after the end of the Second World War, and were designed to take advantage of experience gained by studying German Type XXI U-boats and British wartime experiments with the submarine Seraph, which was modified by streamlining and fitting a bigger battery.

[1] Propulsion machinery consisted of two Admiralty Standard Range diesel generators rated at a total of 3,680 brake horsepower (2,740 kW), which could charge the submarine's batteries or directly drive the electric motors.

[1] Narwhal was laid down at Vickers-Armstrongs' Barrow-in-Furness shipyard on 15 March 1956, was launched on 25 October 1957 and completed on 4 May 1959.

[1][4] Narwhal ran aground at the entrance to Campbeltown Loch, Scotland, on 4 April 1960.

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