Nike-X was a proposed US Army anti-ballistic missile (ABM) system designed to protect major cities in the United States from attacks by the Soviet Union's ICBM fleet. The name referred to its experimental basis, it was intended to be replaced by a more appropriate name when the system was put into production. This never came to pass; the original Nike-X concept was replaced by a much more limited defense system known as the Sentinel program that used some of the same equipment.