'Selenium' was a British two-part naval minelaying and naval air offensive ('Selenium I' and 'Selenium II') against German shipping off the west coast of German-occupied Norway (10/13 February 1945).

The offensive was of particular importance to the Allies, as Adolf Hitler’s insistence that Norway was a 'zone of destiny' meant that at the time of the Finnish/Soviet armistice of 4 September 1944, which ended the 'Jatkosota' continuation war, there were in northern Norway and Finland seven divisions (170,000 men) which the German authorities wished to evacuate from Narvik, the primary shipment port for the Swedish iron ore on which Germany placed so great an industrial reliance. By the beginning of 1945 the evacuation was in progress using some 200 ships (380,000 tons) reserved in northern Norway against just such an eventuality.

The British realised that the evacuation was wholly dependent on the delivery of motor transport and bunker fuel to Narvik by German tankers, and thus decided on a major effort (by warships, submarines, coastal craft and the attack aircraft of Air Vice Marshal S. P. Simpson’s No. 18 Group of Air Chief Marshal Sir William Sholto Douglas’s RAF Coastal Command) to prevent the arrival of this fuel.

Overall command was vested in Admiral Sir Henry Moore, commanding the Home Fleet, who had to contend with imprecise intelligence, the difficulty of Norwegian coastal waters and the vagaries of the winter weather.

Nevertheless, some significant successes were gained. On 6/8 January the Norwegian-manned craft of the 54^th Motor Torpedo Boat Flotilla sank three laden iron-ore transports. On 11/12 January the heavy cruiser Norfolk and light anti-aircraft cruiser Bellona under the command of Rear Admiral R. R. McGrigor sank two merchantmen and one of six escorts in 'Spellbinder'. Aircraft also laid mines during the same month, in which the Allied tally was 12 ships of 20,043 tons sunk, which was almost the same as that achieved by the aircraft of No. 18 Group. The 'Halfback' sweep was also undertaken against three German destroyers which left Narvik on 26 January to move into the Baltic, and though one German ship was heavily damaged and another less badly afflicted, two of the destroyers reached Kiel on 1 February. The fourth large German destroyer in northern Norway sailed on 5 February for the Baltic, joining the repaired destroyer of the earlier movement; both were again hit, this time by bombs, but made it to Kiel during March.

'Selenium' proper was undertaken by the escort carriers Premier and Puncher, the heavy cruiser Devonshire, the light anti-aircraft cruiser Dido, and the destroyers Cavalier, Cavendish, Myngs, Savage, Scorpion, Scourge and Zebra of the 23^rd Destroyer Flotilla. 'Selenium I' took the form of an anti-shipping sweep between Bud and Kvatholm, and 'Selenium II' of minelaying in the Skatestrommen.