In 1940 Ernst Udet originated the Zwilling concept while creating an aircraft capable of towing the Me.321 and the Ju.322 giant cargo gliders. The success of the marriage of two He.111 airframes led Messerschmitt engineers to consider the possibility of creating a heavy fighter on the base of two Bf.109 without disruption of production lines while starting the serial manufacture. Two Bf.109F were converted into the Zwilling at the end of 1942. Both fuselages with DB-601E-1 engines were unchanged except for keel beam for ETC-250 bomb rack mounting and for landing gear mounting closer to fuselage centerline. The Bf-109Z prototype was completed in 1943. The take off weight – 5900 kg, the wing span – 13.3 m, the distance between two fuselages – 3.3 m. The aircraft was ready for flight tests while it was severely damaged during a bombing raid. For comparison, at the end of the 1943, the creation of the analogical variant the North American P-51 Mustang was started, and the first P-82 Twin Mustang made its maiden flight in April 1945.