Minuteman II Development History
Even as the Minuteman I program raced forward, the Air Force began developing the new Minuteman II. The new missile was a significant improvement over its predecessor. A new second-stage motor with a single nozzle and a secondary liquid injection for thrust vector control increased the missile's range from 6,300 to 7,000 miles. The new motors also enabled the Minuteman to carry the larger W-56 warhead with a yield of 1.2 megatons. An improved guidance system made the missile more accurate, and it could store a larger number of preprogrammed targets within its internal memory. Moreover, Minuteman II also carried penetration aids to camouflage the reentry vehicle during reentry.
The Air Force awarded Boeing the Minuteman II contract in March 1962 and the Seattle-based contractor conducted the first test flight in September 1964.
The Minuteman II was a tremendous improvement over Minuteman I. Although the new ICBM was only 2 feet taller and 8,000 pounds heavier than its predecessor, a new second-stage engine extended the missile's range from 6,300 to 7,000 miles and increased the payload to enable it to carry a 1.2-megaton warhead. Minuteman II was also equipped with a new Autonetics guidance system that narrowed the circular error probable (CEP) to 1.5 miles at maximum range. The Air Force calculated that Minuteman II's greater range, larger warhead, and improved accuracy gave it eight times the "kill" capability of Minuteman I.
In May 1966 SAC placed its first Minuteman II squadron on operational alert, and by April 1967 accepted its 200th Minuteman II. At that point the Minuteman force stood at 1,000 missiles; 800 Minuteman Is and 200 Minuteman IIs. Continuing its missile modernization effort, throughout the late 1960s the Air Force replaced many of its Minuteman Is with Minuteman IIs, and by May 1969 it had 500 Minuteman Is and an equal number of Minuteman 11s on operational alert.