The acronym SAM described surface-to-air missiles used by the North Vietnamese against United States Navy and Air Force bombers and fighter-bombers. The standard SAM was the Soviet SA-2 Guideline, a two-stage missile equipped with a 285-pound warhead and a maximum range of 30 miles. The first SA-2 Guidelines were deployed in the summer of 1965, and by the end of the war more than 200 SA-2 sites were operational, most of them protecting Hanoi and Haiphong. Because of the United States "Wild Weasel" program and various other electronic jamming efforts, the North Vietnamese used 150 SA-2s for every American aircraft they destroyed.