The war ended well before the first production units were operational. In the postwar era, Strategic Air Command used the planes as a long-range escort fighter. The first three North Korean aircraft destroyed by U.
Such missions were part of the planned U. It consisted of a twin-fuselage design, somewhat similar to the experimental German Messerschmitt Bf Z "Zwilling". Although based on the lightweight experimental XPF, which would later become the PH Mustang, it was actually a new design. These were mounted to a newly designed center wing section containing the same six. The two vertical tails were also from the XPF, but incorporated large dorsal fillets for added stability in case of an engine failure.
The aircraft had a conventional landing gear with both wheels retracting into bays under each fuselage center section. Initially, the left engine was a V with an additional gear in the propeller reduction box to allow the left propeller to turn opposite to the right propeller, which was driven by the more conventional V In this arrangement both propellers would turn upward as they approached the center wing, which in theory would have allowed better single-engine control.
This proved not to be the case when the aircraft refused to become airborne during its first flight attempt. After a month of work North American engineers finally discovered that rotating the propellers to meet in the center on their upward turn created sufficient drag to cancel out all lift from the center wing section, one quarter of the aircraft's total wing surface area.
The engines and propellers were then exchanged, with their rotation meeting on the downward turn, and the problem was fully solved. The first XP prototype was completed on 25 May , and made the type's first successful flight on 26 June This aircraft was accepted by the Army Air Forces on 30 August , whose officials were so impressed by the aircraft, while still in development, that they ordered the first production PBs in March , fully three months before its first flight.
