A fighter aircraft is a military aircraft designed primarily for attacking other aircraft, as opposed to a bomber, which is designed to attack ground targets, primarily by dropping bombs. Fighters are comparatively small, fast, and maneuverable. They were developed in response to the fledgling use of aircraft and dirigibles in World War I for reconnaissance and ground attack roles. These early fighters were mostly woodenbiplane with light machin guns As aerial warfare became increasingly important, so did control of the airspace. By World War II, fighters were predominantly metal monoplanes with wing-mounted cannon. Following the war, turbojets replaced piston engines as the means of propulsion, and missiles augmented or replaced guns. For historical purposes, jet fighters are classified by generation. The generation terminology was initiated by Russian defense parlance in referring to the F-35 Lightning II as a "fifth-generation" plane. Years are not exact and intended as a guideline. Modern jet fighters are predominantly powered by one or two turbofan engines, armed primarily with missiles (from as few as two on some lightweight day fighters to as many as eight to ten on air superiority fighters like the Su-27 Flanker or F-15 Eagle), with a cannon as backup armament (typically between 20 and 30mm in calibre), and equipped with a radar as the primary method of target acquisition.
Fighter aircraft are the primary means by which armed forces gain air superiority. At least since World War II, air superiority has been a crucial component of victory in most modern warfare, particularly "conventional" warfare between regular armies, and their acquisition and maintenance represent a very substantial proportion of military budgets in militaries that maintain modern fighter forces.