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.[1] The submarines had a length of 208feet overall, a beam of 24feet and a mean draught of 11feet. They displaced 768LT on the surface and 960LT submerged.[2] The S-class submarines had a crew of 40 officers and ratings. They had a diving depth of 300feet.[3]
For surface running, the boats were powered by two 7750NaN0 diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 650hp electric motor. They could reach 13.75kn on the surface and underwater.[4] On the surface, the second-batch boats had a range of 6000nmi at and 64nmi at submerged.[3]
The S-class boats were armed with six 21-inch (533 mm) torpedo tubes in the bow. They carried six reload torpedoes for a total of a dozen torpedoes. They were also armed with a 3-inch (76 mm) deck gun.[2]
Ordered on 2 March 1936, Sterlet was laid down on 14 July 1936 in HM Dockyard, Chatham and was launched on 22 September 1936. The boat was completed on 6 April 1938.[5]
At the onset of the Second World War, Sterlet was a member of the 2nd Submarine Flotilla. From 23–26 August 1939 the 2nd Submarine Flotilla transferred to its war bases at Dundee and Blyth.[6]
On 8 April 1940 Sterlet left for a patrol in the Skagerrak, off Norway under the command of Lt. Gerard Henry Stacpoole Haward. Four days later she unsuccessfully attacked a convoy of three merchant ships and a destroyer. The following day she was assigned a new patrol area and on 14 April torpedoed the German gunnery training ship, leading to her sinking the following day.[7]
She was possibly sunk by the German anti-submarine trawlers UJ-125, UJ-126 and UJ-128 on 18 April. Alternatively, she may have struck a mine whilst returning to port.[8]