Mittelbau-Dora (also Dora-Mittelbau and Nordhausen-Dora) was a German Nazi concentration camp located near Nordhausen in Thuringia, Germany. It was established in late summer 1943 as a subcamp of Buchenwald concentration camp, supplying labour for extending the nearby tunnels in the Kohnstein and for manufacturing the V-2 rocket and the V-1 flying bomb. In the summer of 1944, Mittelbau became an independent concentration camp with numerous subcamps of its own. In 1945, most of the surviving inmates were evacuated by the SS. On 11 April 1945, US troops freed the remaining prisoners. Around one in three of the roughly 60,000 prisoners who were sent to Mittelbau did not survive.