The Northrop P-61 Black Widow, named for the American spider, was the first operational U.S. warplane designed as a night fighter, and the first aircraft designed to use radar. The P-61 had a crew of three pilot, gunner, and radar operator. It was armed with four 20 mm (.79 in) Hispano M2 forward-firing cannons mounted in the lower fuselage, and four .50 in (12.7 mm) M2 Browning machine guns mounted in a remote-controlled dorsal gun turret. It was an all-metal, twin-engine, twin-boom design developed during WWII. The first test flight was made on May 26, 1942, with the first production aircraft rolling off the assembly line in October 1943. The last aircraft was retired from government service in 1954.