The Northrop P-61 Black Widow, named for the American spider, was the first operational U.S. military aircraft designed specifically for night interception of opposing aircraft, and was the first aircraft specifically 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. (Source Wikipedia)