Two prototype aircraft were built, but the end of World War II changed priorities and the advent of the jet engine gave an alternative way toward achieving high speed.

This resulted in an Air Force contract for two prototypes and one static test airframe, the USAAF seeing an intriguing possibility of finding a bomber capable of the Boeing B-29 Superfortress's range without its size or cost.

The landing gear was tricycle and a full, four surface cruciform tail was fitted, whose ventral fin/rudder unit incorporated a tailwheel to prevent the coaxial propellers from striking the ground.

The guns had a limited field of fire (25 degrees left right and +20 -15 in elevation) to the rear, but with the aircraft's high speed it was thought unlikely that intercepting fighters would attack from any other angle.

[1] Considering the danger of bailing out and being pushed into the rear propellers, designers installed an explosive arrangement to sever the props from the tailcone in event of an emergency.

Due to the ventral vertical stabilizer and rudder surface set's tip being located underneath the fuselage, careful handling during taxiing, takeoff, and landing was required because of limited ground clearance.

In December 1945, Captain Glen Edwards and Lt. Col. Henry E. Warden set a transcontinental speed record by flying the second prototype XB-42 (43-50225) from Long Beach, California to Bolling Air Force Base in Washington, D.C. (c. 2,300 miles).

[citation needed] The remaining prototype was used in flight test programs, including fulfilling a December 1943 proposal by Douglas to fit uprated engines and underwing Westinghouse 19XB-2A axial-flow turbojets of 1,600 lbf (7.1 kN) thrust each, making it the XB-42A.