Thrust from a Titan 3/Centaur rocket launched NASA's Viking 1 spacecraft on a 505-million-mile journey to Mars on Aug. 20, 1975. Viking 2 followed three weeks later.
Each mission included both an orbiter and a lander, and all four components accomplished successes. On July 20, 1976, the Viking 1 lander returned the first photograph taken on the surface of Mars. That lander in a region called Chryse Planitia operated until Nov. 13, 1982. The Viking 2 lander operated in the Utopia Planitia region from Sept. 3, 1976 to April 11, 1980. The orbiters sent home images of the entire planet at resolutions of 300 meters (984 feet) or less per pixel.
More information on Viking at: http://marsprogram.jpl.nasa.gov/programmissions/missions/past/viking/