Several German aircraft manufacturers proposed designs for the wartime “Amerikabomber” project, including Junkers, Messerschmitt, Heinkel, Focke-Wulf and Horten Brothers. Only two companies, Junkers and Messerschmitt built prototype aircraft for the project, Junkers Ju 390 and Messerschmitt Me 264. The others only had plans or incomplete examples for the aircraft.

The Junkers Ju 390 was derived from the 4-engine multi-role aircraft Junkers Ju 290. Notable differences between the Ju 290 and Ju 390, two additional engines (for a total of 6 engines) were added to the Ju 390 along with additional wing sections and a fuselage section to lengthen the body. The first test flight of the Ju 390 took place in October 1943. The Luftwaffe intended to order 26 aircraft, but by June 1944 the order was cancelled. Only two aircraft had been produced by that time, only the first version flew.

The design of the Me 264 started with a long-range reconnaissance aircraft project in the 1930s. In early 1942 six prototypes were ordered and that was later reduced to three. The first prototype Me 264 flew in December 1942. The appearance of the Me 264 was very similar to the US Boeing B-29 Superfortress (which was designed earlier than the Me 264). The Me 264 project was cancelled in September 1944.

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