A defense readiness condition (DEFCON) is an alert posture used by the United States armed forces. The DEFCON system was developed by the Joint Chiefs of Staff and unified and specified combatant commands. It prescribes five graduated levels of readiness (or statuses of alert) for the U.S. military, and increase in severity from DEFCON 5 (least severe) to DEFCON 1 (most severe) to match varying military situations.
DEFCONS are a subsystem of a series of Alert Conditions, or LERTCONs, that also includes Emergency Conditions (EMERGCONs).3
DEFCONs should not be confused with similar systems used by the U.S. military, such as Force Protection Conditions (FPCONS) and Watch Conditions (WATCHCONS), or the Homeland Security Advisory System used by the United States Department of Homeland Security. The highest confirmed DEFCON ever was Level 2 (DEFCON2). Movies and popular culture often misuse the DEFCON system by "going to DEFCON 5" during a state of emergency. In fact, DEFCON 5 is the lowest state of readiness. DEFCON 1 is the most severe.