DEFCON The defense readiness condition ( DEFCON ) is an alert state 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 states 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 LERTCON s , that also includes Emergency Conditions ( EMERGCONs ) . There is no single DEFCON status for the country , and in fact different branches of the military can be at different levels of DEFCON at the same time . DEFCONs should not be confused with similar systems used by the U . S . military , such as Force Protection Condition s ( FPCONS ) , Readiness Conditions ( REDCONS ) , Information Operations Condition ( INFOCON ) and its future replacement Cyber Operations Condition ( CYBERCON ) , and Watch Conditions ( WATCHCONS ) , or the former Homeland Security Advisory System used by the United States Department of Homeland Security . Levels . DEFCONs vary between many commands and have changed over time , and the United States Department of Defense uses exercise terms when referring to the DEFCONs . This is to preclude the possibility of confusing exercise commands with actual operational commands . On 12 January 1960 , NORAD " proposed the adoption of the readiness conditions of the JCS system " , and information about the levels was declassified in 2006 : 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 . The highest state , DEFCON 1 , has never been called for . History . After NORAD was created , the command used different readiness levels ( Normal , Increased , Maximum ) subdivided into eight conditions , e . g . , the " Maximum Readiness " level had two conditions " Air Defense Readiness " and " Air Defense Emergency " . In October 1959 , the JCS Chairman informed NORAD " that Canada and the U . S . had signed an agreement on increasing the operational readiness of NORAD forces during periods of international tension . " After the agreement became effective on 2 October 1959 , the JCS defined a system with DEFCONs in November 1959 for the military commands . The initial DEFCON system had " Alpha " and " Bravo " conditions ( under DEFCON3 ) and Charlie / Delta under DEFCON4 , plus an " Emergency " level higher than DEFCON1 with two conditions : " Defense Emergency " and the highest , " Air Defense Emergency " ( " Hot Box " and " Big Noise " for exercises ) . For much of the Cold War , American ICBM sites were at DEFCON 4 , rather than 5 . DEFCON 2 . Cuban Missile Crisis . The highest confirmed DEFCON ever was Level 2 . During the Cuban Missile Crisis on October 22 , 1962 , the U . S . Armed Forces were ordered to DEFCON 3 . On October 26 , Strategic Air Command ( SAC ) was ordered to DEFCON 2 , while the rest of the U . S . Armed Forces remained at DEFCON 3 . SAC remained at DEFCON 2 until November 15 . DEFCON 3 . Yom Kippur War . The U . S . Armed Forces were at DEFCON 3 status during the 1973 Yom Kippur War . September 11 attacks . The third time the United States reached DEFCON 3 was during the September 11 attacks of 2001 . U . S . Secretary of Defense Donald Rumsfeld ordered the increased DEFCON level and to stand by for an increase to DEFCON 2 , which never came . Operations . The DEFCON level is controlled primarily by the U . S . President and the U . S . Secretary of Defense through the Chairman of the Joint Chiefs of Staff and the Combatant Commander s , and each DEFCON level defines specific security , activation and response scenarios for the troops in question . Different branches of the U . S . Armed Forces ( like the U . S . Army , U . S . Navy , Air Force ) and different bases or command groups can be activated at different defense conditions . There is no single DEFCON status for the country , as they are decided on an individual basis by respective branches of the military .