In January 1943, as part of an effort to increase fighter production, Messerschmitt licensed an SS-owned company, DEST, to manufacture Bf 109 parts at Flossenbürg concentration camp. Messerschmitt provided skilled technicians, raw materials, and tools and the SS provided prisoners, in a deal that proved highly profitable for both parties. Production at Flossenbürg started in February. The number of prisoners working for Messerschmitt increased greatly after the bombing of Messerschmitt's Regensburg plant on 17 August 1943. Erla, a subcontractor of Messerschmitt, established Flossenbürg subcamps to support its production: a subcamp at Johanngeorgenstadt, established in December 1943, to produce tailplanes for the Bf 109, and another subcamp at Mülsen-St. Micheln which produced Bf 109 wings, in January 1944. The Flossenbürg camp system had become a key supplier of Bf 109 parts by February 1944, when Messerschmitt's Regensburg plant was bombed again during "Big Week". Increased production at Flossenbürg was essential to restoring production in the aftermath of the attacks.