In 1944, Junkers helped Dornier with work on the Do 335 Zwilling or Dornier Do 635. A meeting was arranged between Junkers and Heinkel engineers, after the meeting, they began work on the project, called 1075 01-21. The designer, Professor Heinrich Hertel, planned for test flight in late 1945. At the end of 1944, the Germans reviewed aircraft designs with the Japanese military, among other projects the Do 635 impressed the Japanese military by its capabilities and design. 
This design consisted of two Do 335 fuselages joined by 2 wings and also having 2 Rb 50 cameras in the port fuselage to take aerial photos. Armament was confined to the provision for five 60 kg (130 lb) target marker bombs. The main wheels were common with Ju 352 wheels. It was also intended that two Walter Rocket Assisted Take Off units would be fitted. In early 1945, a wind-tunnel model was tested, and a cockpits mock-up was constructed, but in February 1945, due to the desperate war situation, the project was cancelled.