The DEFCON level is controlled primarily by the U.S. ĭEFCONs are a subsystem of a series of Alert Conditions, or LERTCONs, which also include Emergency Conditions (EMERGCONs). It increases in severity from DEFCON 5 (least severe) to DEFCON 1 (most severe) to match varying military situations, with DEFCON 1 signalling the outbreak of nuclear warfare. It prescribes five graduated levels of readiness (or states of alert) for the U.S.

The DEFCON system was developed by the Joint Chiefs of Staff (JCS) and unified and specified combatant commands. The defense readiness condition ( DEFCON) is an alert state used by the United States Armed Forces. For other uses, see Defcon (disambiguation).