The second batch of S-class submarines were designed as slightly improved and enlarged versions of the earlier boats of the class and were intended to operate in the North and Baltic Seas.

[2] Ordered on 15 March 1934, Seawolf was laid down on 25 May 1934 in Scotts Shipbuilding & Engineering's shipyard in Greenock and was launched on 28 November 1935.

[6] On 6 October 1939, she attacked the German light cruiser Nürnberg and the torpedo boat Falke in the Skagerrak, but none of the targets were hit.

On 6 March 1942, Seawolf sighted Tirpitz, along with her escorting destroyers Z5 Paul Jacobi, Z14 Friedrich Ihn, Z7 Hermann Schoemann and Z25.

Seawolf arrived in Halifax, Nova Scotia in 1943 to help the Royal Canadian Navy in anti-submarine warfare training.