According to a declassified presidential memo from the Office of the Secretary of Defense to President Lyndon Johnson, the United States was researching an ABM system (the NIKE-X) during the early 1960s as part of its Cold War nuclear arms race against the Soviet Union. One purpose for deploying the NIKE-X system was counterforce protection – i.e. protecting U.S. land-based strategic nuclear forces from Soviet nuclear attack. This suggests that early theoretical applications of ABM systems included possible nuclear warfighting plans. However, as the three-page preview of this document below reveals, the Office of the Secretary of Defense eventually argued against deploying the NIKE-X because of fears the system would destabilize the United States’ robust strategic nuclear deterrence posture.