The F-20 Tigershark (initially F-5G) was a privately financed fighter aircraft, designed and built by Northrop in the USA, starting in 1975. It was a further evolution of Northrop's F-5 Freedom Fighter, although ultimately it shared little more than a strong family resemblance to that aircraft. It was originally designated F-5G, which was approved by the USAF in May 1981. The USAF gave approval for F-20 designation use in November 1982 and of the extra name Tigershark in March 1983. The initial request for F-20 was initially turned down in 1982, the USAF proposing F-19 which ended up not being used at all.
The main change was the replacement of the F-5's two General Electric J85 engines with a single General Electric F404 turbofan, increasing its total thrust by 60%. Like the F-5, however, it was designed as a low-cost, high-performance fighter plane that was easy to maintain. It could reach speeds of Mach 2.1 and had a ferry range of 1,715 miles (2760 km). The aircraft was armed with General Electric AN/APG-67 radar that offered significant performance improvement over the original Emerson AN/APQ-159 and AN/APG-69 radars of the original F-5.
The F-20 made its first flight on August 30, 1982, and a total of three prototypes were created. It was intended for sale to foreign countries and militaries, but the market for the plane never developed, as President Ronald Reagan relaxed the restrictions on selling fighters such as the F-16 Fighting Falcon to other countries. Also, the fact that the United States government had not placed an order for the aircraft had a large effect on the decisions of other countries to buy the F-20 or not. The Pakistan Air Force was offered the F-20 and A-10 Thunderbolt II, but insisted on choosing the F-16 because it would give them a technological advantage. Currently Pakistan is involved in the development of a very similar aircraft to the Tigershark,the JF-17. In 1986 China signed a US$550 million agreement with Grumman to modernise its J-7. The project was cancelled in early 1990 and restarted in the form of the JF-17 thunder project. It is alleged that Grumman used the F-20 plan as a final target for the upgrading the F-7.