High Quality Content by WIKIPEDIA articles! The LGM-118A Peacekeeper, also known as the MX missile (for Missile-eXperimental), was a land-based ICBM deployed by the United States starting in 1986. The Peacekeeper was a MIRV missile; it could carry up to 10 re-entry vehicles, each armed with a 300-kiloton W87 warhead/MK-21 RVs. A total of 50 missiles were deployed after a long and troubled development period.