The DEFCON system was developed by the Joint Chiefs of Staff (JCS) and unified and specified combatant commands. It prescribes five graduated levels of readiness (or states of alert) for the U.S. military. It increases in severity from DEFCON 5 (least severe) to DEFCON 1 (most severe) to match varying military situations.
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 Commanders, and each DEFCON level defines specific security, activation and response scenarios for the troops in question.
Different branches of the U.S. Armed Forces (i.e. U.S. Army, U.S. Navy, Air Force) and different bases or command groups can be activated at different defense conditions. In general, there is no single DEFCON status for the world or country and it may be set to only include specific geographical areas. According to Air & Space/Smithsonian, as of 2014, the worldwide DEFCON level has never risen higher than DEFCON 3. The DEFCON 2 levels in the Cuban Missile Crisis and 1991 Gulf War were not worldwide.
There is no single DEFCON status for the country, and in fact different branches of the military can be at separate defense readiness conditions at the same time. DEFCONs should not be confused with similar systems used by the U.S. military, such as Force Protection Conditions (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.
Defense readiness conditions 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 1966, NORAD "proposed the adoption of the readiness conditions of the JCS system", and information about the levels was declassified in 2006:
|Readiness condition||Exercise term||Description||Readiness|
|DEFCON 1||COCKED PISTOL||Nuclear war is imminent||Maximum readiness|
|DEFCON 2||FAST PACE||Next step to nuclear war||Armed Forces ready to deploy and engage in less than 6 hours|
|DEFCON 3||ROUND HOUSE||Increase in force readiness above that required for normal readiness||Air Force ready to mobilize in 15 minutes|
|DEFCON 4||DOUBLE TAKE||Increased intelligence watch and strengthened security measures||Above normal readiness|
|DEFCON 5||FADE OUT||Lowest state of readiness||Normal readiness|
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).
Cuban Missile Crisis
During the Cuban Missile Crisis on October 22, 1962, the U.S. Armed Forces (with the exception of United States Army Europe (USAREUR)) were ordered to DEFCON 3. On October 24, 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.
As such, the defense readiness framework is not only for emergency response, but also for general force mobilization.
Yom Kippur War
On October 6, 1973, Egypt and Syria launched a joint attack on Israel resulting in the Yom Kippur War. The U.S. became concerned that the Soviet Union might intervene, and on October 25, U.S. forces, including Strategic Air Command, Continental Air Defense Command, European Command and the Sixth Fleet, were placed at DEFCON 3. Over the following days, the various forces reverted to normal status with the Sixth Fleet standing down on November 17.
Operation Paul Bunyan
Following the axe murder incident at Panmunjom on August 18, 1976, readiness levels for American forces in South Korea were increased to DEFCON 3, where they remained throughout Operation Paul Bunyan which followed thereafter.
September 11 attacks
During the terrorist attacks of September 11, 2001, the U.S. Secretary of Defense Donald Rumsfeld ordered the increased DEFCON level to 3, and also a stand-by for a possible increase to DEFCON 2. That eventuality however did not come to pass. 
In other media
- DEFCON was used significantly in the films WarGames, Thirteen Days, Watchmen, Independence Day, The Sum of All Fears, By Dawn's Early Light, Crimson Tide, White House Down, Canadian Bacon and Olympus Has Fallen.
- The real-time strategy game DEFCON simulates the outbreak of thermonuclear war, and advances through the DEFCON levels as each match progresses.
- The Cold War-based board game Twilight Struggle features DEFCON as a key element of gameplay. Gameplay becomes more and more restrictive as the DEFCON level deteriorates. A player who raises DEFCON level to DEFCON 1 is deemed to have initiated thermonuclear war and loses the game immediately.
- In Tropico 4, the seventh mission (named "Crisis") of the game campaign is built upon DEFCON, where player's actions directly affect DEFCON levels.
- The stealth game CounterSpy has players infiltrating opposing bases to prevent their DEFCON levels reaching critical.
- British dance-rock band Pop Will Eat Itself has a song titled "Def. Con. One" on their 1989 album This Is the Day...This Is the Hour...This Is This!
- In 2002 Dutch hard-dance festival organizer Q-Dance had created a hardstyle event called Defqon.1 Festival which premiered 14 June 2003 and would later premiere in other countries years later.
- In Zombies mode of Call of Duty: Black Ops, in the map "Five", set in the Pentagon, the DEFCON level is immediately at 1, and players can reduce the level to access other areas usually in lockdown.
- DEFCON was used frequently in the Canadian-American Science fiction series Stargate SG1
|Wikimedia Commons has media related to DEFCON.|
- Doomsday Clock
- HURCON – Hurricane Condition threat rating (military-developed scale)
- National Command Authority
- National Military Command Center
- UK Threat Levels – Similar British system used for terrorism threats
- "Department of Defense Dictionary of Military and Associated Terms" (PDF). 12 April 2001 (As Amended Through 19 August 2009). Archived from the original (PDF) on 11 November 2009. Retrieved 1 February 2014. (DEFCON is not mentioned in the 2010 and newer document)
- Sagan, Scott D. (Summer 1985). "Nuclear Alerts and Crisis Management" (pdf). International Security 9 (4): 99–139. doi:10.2307/2538543 – via Project Muse.
- "Emergency Action Plan (SEAP)" (PDF). United States Army Corps of Engineers Savannah District (CESAS) Plan 500-1-12. 1 August 2001. Archived from the original (PDF) on 2013-02-03.
- Chiles, James R. (March 2014). "Go To DEFCON 3". Air & Space/Smithsonian.
- Chairman of the Joint Chiefs of Staff Instruction 6510.01F
- "Emergency Action Procedures of the Joint Chiefs of Staff, Volume I - General" (PDF). US DoD FOIA Reading Room. April 24, 1981. pp. 4–7.
- NORAD/CONAD Historical Summary: July -December 1959 (PDF) (Report). Retrieved 2013-09-25.
- "DEFCON DEFense CONdition". fas.org.
- Nighthawks over Iraq, a study a study of the F117-A stealth fighter in operations Desert Shield and Desert Storm
- Jan Goldman (16 June 2011). Words of Intelligence: An Intelligence Professional's Lexicon for Domestic and Foreign Threats. Scarecrow Press. pp. 93–. ISBN 978-0-8108-7476-3.
- Probst, Reed R. (16 May 1977). "Negotiating With the North Koreans: The U.S. Experience at Panmunjom" (PDF). Carlisle Barracks, Pennsylvania: U.S. Army War College. Retrieved 17 December 2009.
- 911 Compmission Report