Designed as a flying model to refine the concepts of the flying wing, N1M was first flown on June 3, 1940. Unlike N1M, it did not have bent wingtips and was a larger and more powerful aircraft. First N9M was flown on December 27, 1942. 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.