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Douglas XB-42 Mixmaster & XB-43 Jetmaster
Prototypes.com/Douglas XB-42 Mixmaster & XB-43 Jetmaster/I. Le XB-42

Translated with typo's...........

The Douglas XB-42 Mixmaster was the first American bomber to reach 400 thousand / hour (644 km / h). Although he was one of the most advanced equipment at the end of the war, he was never mass-produced because the appearance of jets made it obsolete. The engines developed Mixmaster power nearly identical to that of De Havilland Mosquito but the American bomber carried twice loading bombs at the same speed...................

Douglas submit these studies to the Army Air Force (USAF future) in an unsolicited proposal in May 1943. In June 1943, the AAF assigned to Douglas a contract for two prototypes and a static test fuselage. Burton and his team finish a model in September and the first prototype in May 1944..........................

Engines actionnaient of contra-rotating propellers placed in the tail of the bomber. A plurality of drive shafts of the power transmitted to each driving the gearbox in the tail propeller...............One of these drive shafts was also mounted on the Bell P-39 Airacobra. The vertical stabilizer was a dorsal and ventral which also served to prevent the propellers struck the runway.

Douglas XB-43 Jetmaster
https://en.wikipedia.org/wiki/Douglas_XB-43_Jetmaster

The Douglas XB-43 Jetmaster was an American 1940s jet-powered prototype bomber aircraft. The XB-43 was a development of the XB-42, replacing the piston engines of the XB-42 with two General Electric J35 engines of 4,000 lbf (17.8 kN) thrust each. Despite being the first American jet bomber to fly, it suffered stability issues and the design did not enter production.