Description: The first prototype Su-17, redesigned from Su-7B, flew on August 2, 1966. Entered production in 1970. The Su-17 was a large step in the development of the Su-7 to a more useful attack aircraft. The most important change was the introduction of swivelling outer wing panels, improving take-off and landing performance, and thus allowing a larger weapons load. The Su-20 and Su-22 were export versions. Over 3000 were built. Between April 1974 and February 1977 a 27 Su-20/Su-20R (belongs to 66, 74 and 76 series) had been delivered to Polish Air Forces, to 7th Bomber Reconnaissance Squadron only. Polish Su-20 was designed to attack with nuclear bomb. 8 Polish Su-20/Su-20R loses in crashes. Poland was using Su-20 up to February 1997.