F-5 Freedom Fighter is a fighter aircraft, designed and built by Northrop in the USA, beginning in 1962. It was used by the US only as an enemy aircraft for training purposes, but was sold to many friendly foreign countries, since it was relatively inexpensive.
See also freedom fighter, T-38 Talon, F-20 Tigershark
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note: F-5 also refers to the Chinese fighter aircraft J-5. The F-5 designation is often used outside of China.