 Commissioned at Christmas 1942 in Danzig after an exceptionally long building period, "U-735" was given to "Kapitänleutnant" Hans-Joachim Börner, who remained in command of the boat right up to her destruction exactly two years later, when he was killed on board his ship.Dispatched to Norway, Börner soon became an expert on the Norwegian seaways, and was able to train a large number of sailors on his practice missions from Horten.On the 28 December 1944, RAF Bomber Command sought to eradicate the menace of submarines sailing from Norwegian bases, and launched a major raid on Horten.