CZ Mittelbau-Dora was the last large concentration camp the Germans built. It was started as a satellite camp of Buchenwald in August 1943.  By the December of 1944 it had become a separate concentration camp complex with subsidiary camps. 

The prisoners toiled from September 1943 to April 1944 constructing the underground tunnel system to house the factory to produce the V2 (and, later, V1) rockets.  Camp prisoners lived, toiled and died in large numbers inside the tunnel system during its construction. This tunnel construction was devastating to the prisoners. Up to 10,000 prisoners were living under inhuman conditions inside the caves by December 1943.

Production of the V2 in the underground complex "Mittelwerks" began in the spring of 1944. Prisoners were moved into barracks. As the Allied aerial bombing became more effective, production of other weapons systems was moved into these tunnels.