Junkers and Messerschmitt built a few prototype airframes before the end of WWII .
Hillgruber , Andreas Germany and the Two World Wars , Harvard University Press : Cambridge , 1981 pages 50-51 The proposal by the RLM to Germany 's military aviation firms for the Amerika Bomber project was issued to Reichsmarschall Hermann Goering in the late spring of 1942 , about six months after the attack on Pearl Harbor , for the competition to produce such a strategic bomber design.
Invasion of the United States