KIRTLAND AFB, N.M. --   In September 1951, the Air Force awarded Convair a contract to begin design of a ballistic missile, which led to development of the Atlas ICBM. The first Atlas test flight took place June 11, 1957. The Atlas D was the first operational missile and the first Atlas D squadron achieved initial operational capability in March 1961. After the Minuteman become operational in early 1963, the Atlas rapidly became obsolete. By October 1964, all Atlas D missiles had been phased out except those still awaiting test-firing from Vandenberg AFB, Calif. The last Atlas D was test-fired March 12, 1965.