On May 16,1964, Secretary of Defense McNamara directed an accelerated phaseout of Titan I and Atlas ICBMs. Consequently, the Titan Is of the 850th Strategic Missile Squadron were removed from alert status on January 4, 1965. The Air Force subsequently deactivated the squadron on March 25th. Titan's lifespan was short in western South Dakota. In July 1962, Strategic Air Command had effectively rendered it obsolete by activating the 66th Strategic Missile Squadron, the first of three such units slated to operate 150 Minuteman I  ICBMs under the 44th Strategic Missile Wing. The 67th Strategic Missile Squadron joined the 44th in August, followed by the 68th Strategic Missile Squadron in September 1962. On August 21, 1961, construction began on the Minuteman IB facilities. The contract to build the 150 silos and associated launch control facilities was executed by Peter Kiewit Sons’ Company of Omaha, Nebraska, using designs developed by Parsons-Stavens, Architect Engineer, in Los Angeles. Activation of the 44th Strategic Missile Wing on January 1, 1962, marked the initiation of SAC’s first Minuteman “IB” wing. Seven months later, the activation of the 66th Strategic Missile Squadron marked the beginning of SAC’s first Minuteman IB squadron. As men trained for their new duties, progress continued on the silos being constructed on the South Dakota prairie. The work force peaked in September 1962 as the Peter Kiewit work force reached 2,915 workers. While these men worked out on the prairie, construction proceeded at Ellsworth AFB on converting a hanger for a missile support facility. In April 1963, the first missile was emplaced into a prepared silo. Two months later, SAC accepted the first flight of 10 Minuteman IB ICBMs and in July, some of these missiles were placed on alert status.