These figures are somewhat suspect and are likely to be optimistic guesses that could not have been realised, something Heinkel was famous for. Propellers lose efficiency as they approach the speed of sound and eventually they no longer provide an increase in thrust for an increase in engine power. The only remaining gain of thrust would come from the piston engine exhausts. The advanced counter-rotating "Vereinigte Deutsche Metallwerke" (VDM)-origin propeller design is unlikely to have been able to counteract this problem. The design apparently received low priority and it was not complete by the end of the war. Siegfried Günter later provided detailed drawings and plans for the Americans in mid-1945.