The outbreak of the Second World War found Severn in the Mediterranean with the 1st Submarine Flotilla stationed at Malta.

In September 1939 she was transferred to West Africa, stationed at Freetown, to act as convoy escort guarding against surface raiders.

This involved searching for U-boats, surface raiders and blockade runners, and she was active in this capacity during the Norwegian campaign.

[2][3][4] She was one of a number of submarines ordered to track the German battleship Bismarck before her eventual sinking.

[1] In January 1944 Severn was assigned to the Eastern Fleet, joining 2nd Submarine Flotilla at Trincomalee in May.