The first operational U.S. aircraft specifically designed as a night-fighter was the P-61 Black Widow. Created in 1940 by Northrop Aviation, in collaboration with the British Royal Air Force, the P-61 was also the first aircraft designed to use radar.
With its mysterious appearance and name, the Black Widow ruled the night in the waning months of World War 2. It would even collect the last confirmed air-to-air kill on the last night of the war...