The Lavochkin OKB S-75 (Russian: С-75; NATO reporting name SA-2 Guideline) is a Soviet designed high-altitude, command guided, surface-to-air missile (SAM) system. Since its first deployment in 1957, it has become the most widely deployed and used air defense missile in history.
This system first gained fame when an S-75 battery shot down a CIA U-2 overflying the Soviet Union in 1960. Later, North Vietnamese forces used the S-75 extensively during the Vietnam War to defend Hanoi and Haiphong. It has also been locally-produced in the People's Republic of China using the names HQ-1 and HQ-2. Other nations have produced so many local variants combining portions of the S-75 system with both indigenously developed components or third party systems, that it has become virtually impossible to find a pure S-75 system today.