The Northrop F-5A/B Freedom Fighter and the F-5E/F Tiger II are part of a family of light supersonic fighter aircraft, initially designed in the late 1950s by Northrop Corporation. Being smaller and simpler than contemporaries such as the McDonnell Douglas F-4 Phantom II, the F-5 cost less to both procure and operate, making it a popular export aircraft. According to Pierre Sprey, it was perhaps the most effective U.S. air-to-air fighter in the 1960s and early 1970s. A small visual and radar cross section size and consequent detection difficulty often conferred the F-5 the advantage of surprise. The aircraft also has a high sortie rate, low accident rate, high maneuverability, and is armed with a combination of 20mm cannon and heat seeking missiles. The flying qualities of the F-5 are often highly rated, comparable to the North American F-86 Sabre and the General Dynamics F-16 Fighting Falcon. Fiscally, it is reportedly unmatched among supersonic fighters, contributing to its long service life.