After refitting during the winter HMS Thames (Lt.Cdr. William Donald Dunkerley, RN) was active in the North Sea in spring 1940 during the Norwegian campaign. In July 1940 Thames torpedoed and sank the German torpedo boat Luchs. Luchs was part of the escort for the damaged German battleship Gneisenau that was on passage from Trondheim, Norway to Kiel, Germany. She was most likely mined off Norway late July 1940 or early August 1940.

On 4 July 1940 HMS Salmon (Cdr. Edward Oscar Bickford, DSO, RN) departed her base to patrol off Skudesnes on the south west coast of Norway. She was sent signals on 9th, 11th and 12th July, the final one ordering a return to harbour. None of these signals were acknowledged. Later it became known that one of the signals routed her across a minefield which at the time was unknown to the Admiralty. There is also a possibility that she was attacked by aircraft, but mining is the most likely somewhere in position 57º20'N, 05º00'E.

On 17 November 1939, Naval High Command (SKL) issued secret orders for U-Boot U-36 and U-38 to scout the location for Basis Nord, a secret German naval base for raids on Allied shipping located off the Kola Peninsula and provided by the Soviet Union. However, U-36 never left the Norwegian Sea. On 4 December 1939, two days out of Wilhelmshaven, U-36 was spotted on the surface near the Norwegian port of Stavanger by the British submarine Salmon. Salmon then fired one torpedo at her unwitting counterpart. It sank U-36 and all 40 of the sailors aboard were lost.

The ORP Orzel departed on her seventh patrol on 23 May, to the central North Sea. On 1 and 2 June a radio message was transmitted from Rosyth ordering her to alter her patrol area and proceed to the Skagerrak. No radio signals had been received from her since she had sailed, and on 5 June she was ordered to return to base. She never acknowledged reception, and never returned to base. 8 June 1940 was officially accepted as the day of her loss. Although various theories exist regarding her loss, and it is commonly believed that she ran on to a mine in the Skagerrak, the true cause of her loss remains unknown to this day