text: The British read these moves from Ultra intercepts and traffic analysis from the RAF Y-station at RAF Cheadle, which eavesdropped on communications between Luftwaffe aircraft and ground stations. The reinforcement of the U-boat force in the Arctic to 12 in March and 21 in August (the real number was later found to be 23) was followed, along with the transfer orders to the large German ships, leading to the ambush of Prinz Eugen by the submarine  off Trondheim on 23 February. Prinz Eugen was badly damaged by a torpedo and the Admiralty was informed of the hit by an Enigma intercept the next day. The information could not always be acted upon because much of it was obtained at short notice but the intelligence did allow the Royal Navy to prepare for battle and convoys could be given appropriate escorting forces. The interception and sinking of Scharnhorst by  was greatly assisted by ULTRA intercepts.
  Literary depictions
  The 1955 novel HMS Ulysses by Scottish writer Alistair MacLean, considered a classic of naval warfare literature and the 1967 novel The Captain by Dutch author Jan de Hartog are set during the Arctic convoys. The two books differ in style, characterisation and philosophy (de Hartog was a pacifist, which cannot be said about MacLean). Both convey vividly the atmosphere of combined extreme belligerent action and inhospitable nature, pushing protagonists to the edge of endurance and beyond. The Norwegian historic account One in Ten Had to Die (Hver tiende mann måtte dø) also 1967 by writer Per Hansson is based on the experience of the Norwegian sailor Leif Heimstad and other members of the Norwegian merchant fleet during World War II. The 1973 Russian novel Requiem for Convoy PQ-17 (Реквием каравану PQ-17) by writer Valentin Pikul depicts the mission of Convoy PQ 17, reflecting the bravery and courage of ordinary sailors in the merchant ships and their escorts, who took mortal risks to provide Allied aid.