Only four N9M were built, one of which was destroyed in a crash. All P-61 have a hump under the fuselage which houses guns. Some versions also have a rotating turret with four machine guns on top of the fuselage. Nose section of the fuselage is very long and it houses the radar. Two booms are attached under the wings on either side of the fuselage.
Booms end in a rounded fin.
High-set wings are unswept with varying chord. Rectangular tailplane is mounted between booms. Landing gear with nose wheel is retractable. First prototype XP-61 was flown on May 26, 1942. Last P-61 were taken out of service in the fall of 1950.