I just saw a picture of this x-plane, not in all my reading have I ever come across this. I looked it up and found this from http://www.nasm.si.edu/research/aero/aircraft/douglas_xb42.htm "The ingenious Douglas XB-42A Mixmaster was America's first 644 kph (400 mph) bomber. One of the most advanced reciprocating-engine aircraft flown, Douglas never produced it because it appeared late in the war as jet-propelled designs rendered nearly every propeller-driven aircraft obsolete. The Mixmaster's engines generated about the same power as the superlative British De Havilland Mosquito but the American bomber carried twice the Mosquito's maximum bomb load at the same speed as the British airplane. The Douglas bomber was also equipped with a powerful defensive armament that the Mosquito lacked. Douglas designer, E.F. Burton, envisioned a bomber powered by two engines buried inside the fuselage. This design innovation could reduce the drag by one-third compared to more conventional bombers. When he compared his design to the Boeing B-29 Superfortress, Burton believed he could develop a faster airplane that would carry a similar bomb load and employ a crew of 3 instead of the 10 airmen needed to man the B-29. Burton believed his Mixmaster would require just half of the maintenance crew required to keep the Superfortress airborne and cost one-third the price of the large, four-engine bomber from Boeing." Too bad it didn't get put into service ahead of the jet age!