BGM - 75 AICBM The Advanced Intercontinental Ballistic Missile , also known as Weapons System 120A ( WS - 120A ) and ZBGM - 75 , was a program to develop an intercontinental ballistic missile ( ICBM ) , proposed by the United States Air Force in the 1960s as a replacement for the LGM - 30 Minuteman as the Air Force ' s standard ICBM . Funding was not allocated for the program and the project was cancelled in 1967 . Background . The Department of Defense began the STRAT - X study on 1 November 1966 to evaluate a new ballistic missile proposal from the Air Force , which was designated the Advanced Intercontinental Ballistic Missile ( AICBM ) . The project was intended to provide a successor to the LGM - 30 Minuteman ICBM then in United States Air Force service . The program was officially launched in April 1966 , and in June the project received the designation ZBGM - 75 , the " Z " prefix indicating a project in the planning stage . The specifications for the ZBGM - 75 called for a large solid - fuel - powered missile , which would be fitted with between 10 and 20 multiple independently targetable reentry vehicle s ( MIRVs ) . The missiles would be based in silo launchers , which were specified to be hardened by a factor of 10 over the existing silos used by Minuteman missiles . In addition , there was also a plan to develop a railroad - based deployment system for the AICBM . Improvements in accuracy over existing missiles , combined with penetration aid s under development to enhance the effectiveness of each missile , were expected to make the AICBM capable of defeating existing and projected Soviet anti - ballistic missile systems . Cancellation . Ultimately , the Navy won the STRAT - X competition with the design that would become the ballistic missile submarine s . Nevertheless , the final report , issued in August 1967 , recommended that the ZBGM - 75 also be developed . Accordingly , the Joint Chiefs of Staff recommended to Secretary of Defense Robert McNamara that the ZBGM - 75 be funded starting in Fiscal Year ( FY ) 1969 , with a projected entry into service by 1973 . This recommendation came after the Air Force had completed the preliminary studies on the missiles and the new , hardened silos . McNamara instead kept the missile in " advanced development " , which stopped all work on the project . Only development of the new super - hardened silos was approved for funding ; these would be used by the Minuteman missiles . As a result the missile ' s development was cancelled . McNamara ' s rationale for cancelling the program was the destabilizing influence of the new missile , which could have rendered existing Soviet anti - ballistic missile defenses ineffective . McNamara saw relative parity between the two powers — the strategic basis for mutually assured destruction — as the best method to keep the Soviet Union in a position where it must negotiate with the United States . After the cancellation of WS - 120A , the Air Force made no further development of new ICBMs until 1972 . In that year the M - X project was begun , which resulted in the development of the LGM - 118 Peacekeeper . The Peacekeeper entered service in the mid - 1980s and served until 2005 ; the Minuteman III is still in service , and has outlasted both of its planned replacements . References . Notes Bibliography