 Following her sea trials and warming-up period, "U-821" departed Bergen, Norway in March 1944 for her first war patrol, during which she spent 24 fruitless days in the North Atlantic before returning to Brest, France for resupply.Her second patrol was more eventful, as just four days out from Brest and not far from Ushant, Royal Air Force aircraft spotted and attacked the U-boat on the surface.Her captain made the decision to battle it out rather than dive, and engaged in a running firefight with three Mosquito aircraft of 248 Squadron and a large Consolidated Liberator bomber of 206 Squadron.