Northrop F-5 Freedom Fighter
Design and Development

Originally designed by Northrop (designated N-156) as a low-cost, low-maintenance fighter, there was little market for such a craft. It was designed around a pair of afterburning versions of the General Electric J85, which was originally designed to power the tiny McDonnell ADM-20 Quail decoy then carried by the B-52 bomber. This requirement created a very small engine with a very high thrust to weight ratio. The U.S. Army expressed interest in it for ground support, but operating fixed-wing aircraft was a task largely taken over by the U.S. Air Force. The Air Force would neither agree to operate the N-156 nor to allow the Army to operate fixed-wing combat aircraft (a situation repeated with the C-7 Caribou).

When the Military Assistance Program under the Kennedy Administration needed a low-cost fighter for distribution to less-developed nations, the N-156F was at the top of the pile, and subsequently became the F-5A. It was named under the 1962 United States Tri-Service aircraft designation system which included a re-set of the fighter number series (the General Dynamics F-111 was the highest sequentially numbered P/F- aircraft to enter service under the old number sequence).

The F-5 proved to be a successful combat aircraft for US allies, but never entered front-line service with the US due to diverging priorities of the US services. The USAF did adopt the T-38 Talon trainer version of the airframe as the world's first supersonic trainer, and the design would be the starting point for the YF-17, which was developed into the F/A-18 Hornet. Although the F-5 was a lightweight fighter built around what was once an engine for a decoy drone, its descendant, the F/A-18E/F Super Hornet, is a relatively heavy multirole plane.

Wikipedia: F-5 Freedom Fighter