During the Second World War , Nuremberg was the headquarters of Wehrkreis (military district) XIII, and an important site for military production, including aircraft, submarines and tank engines. A subcamp of Flossenbürg concentration camp was located here. Extensive use was made of slave labour .  The city was severely damaged in Allied strategic bombing from 1943 to 1945. On 29 March 1944, RAF endured its heaviest losses in the bombing campaign of Germany. Out of more than 700 planes participating, 106 were shot down or crash landed on the way home to their base, and more than 700 men were missing, as many as 545 of them dead. More than 160 became prisoners of war.  On 2 January 1945, the medieval city centre was systematically bombed by the Royal Air Force and the . Army Air Forces and about ninety percent of it was destroyed in only one hour, with 1,800 residents killed and roughly 100,000 displaced. In February 1945, additional attacks followed. In total, about 6,000 Nuremberg residents are estimated to have been killed in air raids.