'Polarnacht' was the German deployment of the battleship Tirpitz from Wilhelmshaven in northern Germany to Trondheim on the north-west coast of German-occupied central Norway (14/17 January 1942).

After her sea trials, which began in February 1941, Tirpitz was based at Kiel and underwent a period of intensive working-up training in the Baltic. While Tirpitz was based at Kiel, Germany began its 'Barbarossa' invasion of the USSR in June 1941, and a temporary Baltic fleet was created under the command of Vizeadmiral Otto Ciliax to handle any possible break-out of Vitse Admiral Vladimir F. Tributs’s Baltic Fleet from its bases at the eastern end of the Gulf of Finland near Leningrad. Tirpitz was briefly the flagship of the German Baltic fleet, which otherwise comprised the heavy cruiser (ex-pocket battleship) Admiral Scheer, the light cruisers Emden, Köln, Leipzig and Nürnberg, several destroyers, and two flotillas of minesweepers. This fleet patrolled off the Åland islands group from 23 to 26 September, after which it was disbanded and Tirpitz resumed her training programme. During this period, Tirpitz tested her primary and secondary guns on the old pre-dreadnought battleship Hessen, which had been converted into a radio-controlled target ship.

On 13 November Grossadmiral Erich Raeder, commander-in-chief of the German navy, proposed that Tirpitz be deployed to Norway, from which she would be able to sortie in attacks on the Allied convoys bound for the USSR, as well as to serve as a 'fleet in being' in order to tie down British naval assets and deter any Allied invasion of Norway. Adolf Hitler, who had forbidden any Atlantic sortie by German surface warships after the loss of Bismarck, Tirpitz's sister ship, in the 'Rheinübung' operation, agreed to the proposal, and Tirpitz was taken into dockyard hands for the modifications deemed necessary for the new deployment. The ship’s anti-aircraft battery was strengthened and the eight turrets, each carrying two 105-mm (4.13-in) guns, on the superstructure next to the catapult were moved farther outboard to increase their arcs of fire. Two quadruple 533-mm (21-in) torpedo tube mountings were also installed during this refit.

The ship’s commander, Kapitän Karl Topp, pronounced the ship ready for combat operations on 10 January 1942, and on the following day Tirpitz departed for Wilhelmshaven, a move designed to conceal her actual destination.

The battleship left Wilhelmshaven at 23.00 on 14 January and made for Trondheim. British decrypts of intercepted German naval signals detected the departure of the vessel, but poor weather in the UK prevented action by land-based British aircraft. Admiral Sir John Tovey, commander-in-chief of the Home Fleet, was not made aware of Tirpitz‍'s movements until 17 January, well after the ship had arrived in Norway. On 16 January, British aerial reconnaissance located the ship in Trondheim. Tirpitz then moved to the Fættenfjord, just to the north of Trondheim, in 'Polarnacht' with an escort of four destroyers in the form of Richard Beitzen, Paul Jacobi, Bruno Heinemann and Z 29. On arrival, the battleship was moored next to a cliff, which protected the ship from air attacks from the south-west, and the ship’s crew was also used to cut down trees for placement on board Tirpitz as camouflage. Moreover, additional anti-aircraft batteries were installed around the fjord, as were anti-torpedo nets and heavy booms in the entrance to the anchorage.

For lack of adequate numbers of submarines to maintain a constant patrol in the area, the only Allied naval asset available during 'Polarnacht' was the Free Dutch O-14, which was operating in the area of Fro Havet, but this boat was soon supplemented by the British Trident and Seawolf, and then by Tigris and and the Free French Minerve. None of these boats gained contact.