What short lived aircraft, produced for the United States Air Force, is based on a fighter plane armed with four 20 mm cannons?
Northrop F-15 Reporter: The Northrop F-15 Reporter (later RF-61) was an American unarmed photographic reconnaissance aircraft. Northrop P-61 Black Widow:  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.
i don't know