The DFS 40 (originally developed as the Delta V) was a tail-less research aircraft designed by Alexander Lippisch in 1937 as a follow-on to his Delta IV aircraft. In construction, the DFS was more like a flying wing than its predecessor, and was intended to provide a comparison with that aircraft.

The DFS 40 was flown for the first time by Heini Dittmar in 1939, shortly before Lippisch departed the DFS (Deutsche Forschungsanstalt für Segelflug – German Research Institute for Sailplane Flight) to begin work at Messerschmitt. Soon afterwards, without Lippisch there to supervise the project, the aircraft crashed due to an error in centre of gravity calculations that resulted in it entering a flat spin during flight.