Military Alert Levels Explained: DEFCON, FPCON, MOPP and EMCON Compared
The US military runs several alert scales at once, and they measure different things. DEFCON is about readiness for war, nuclear war included. FPCON is about protecting bases and people from terrorist attack. MOPP tells troops how much chemical protective gear to wear. EMCON controls how much a ship or unit transmits. A base can sit at a raised FPCON while DEFCON hasn’t moved at all; a destroyer can go radio-silent under EMCON with no change in either.
News coverage tends to flatten them all into “the military raised its alert level”. This page sets out what each scale measures, its levels, who sets it and when it has been moved in public view. It also covers CPCON, the cyber equivalent.
DEFCON: readiness for war
DEFCON stands for Defense Readiness Condition. The Joint Chiefs of Staff and the unified commands built it in 1959, and it runs from DEFCON 5 (lowest) to DEFCON 1 (highest). The numbers count down as the danger goes up, which is why “DEFCON 1” ended up in films as shorthand for the end of the world.
| Level | Exercise term | Meaning |
|---|---|---|
| DEFCON 5 | FADE OUT | Lowest readiness; normal peacetime posture |
| DEFCON 4 | DOUBLE TAKE | Stronger intelligence watch and security measures |
| DEFCON 3 | ROUND HOUSE | Force readiness raised above normal |
| DEFCON 2 | FAST PACE | One step short of nuclear war; forces ready to deploy within six hours |
| DEFCON 1 | COCKED PISTOL | Nuclear war imminent or under way |
The president and the secretary of defense control the level, working through the chairman of the Joint Chiefs. It doesn’t have to be uniform: different commands can sit at different levels at the same time, and that has happened in most of the famous cases. The current DEFCON is not announced. Websites claiming to show “today’s DEFCON” are guessing.
The publicly known moves:
- Cuban Missile Crisis, October 1962. US forces went to DEFCON 3 during the crisis. On 24 October, Strategic Air Command was ordered to DEFCON 2 while the rest of the armed forces stayed at DEFCON 3. SAC stayed at DEFCON 2 until 15 November. It’s the highest level the US is known to have reached.
- Yom Kippur War, October 1973. On 24 October, Brezhnev warned Nixon that the Soviet Union might act alone in Egypt if the US wouldn’t join a ceasefire force. On 25 October, US forces worldwide, Strategic Air Command included, went to DEFCON 3. The crisis eased the same day when the UN Security Council passed Resolution 340.
- Korean axe murder incident, August 1976. After North Korean soldiers killed two US Army officers in the Joint Security Area on 18 August, US forces in South Korea went to DEFCON 3.
- 11 September 2001. Secretary of Defense Donald Rumsfeld raised the level to DEFCON 3 and put forces on standby for DEFCON 2. It came down to DEFCON 4 on 14 September.
DEFCON 1 has never been declared.
FPCON: protecting bases and people
FPCON, the Force Protection Condition, deals with terrorist threats to US military installations, ships and personnel. It used to be called THREATCON; the name changed in June 2001 because it was too easily confused with the State Department’s threat system. The levels and measures stayed the same. The reforms behind it followed a string of attacks on US forces and facilities: the 1995 Oklahoma City bombing, the 1998 embassy bombings in Kenya and Tanzania, and the attack on USS Cole in 2000.
| Level | Trigger |
|---|---|
| FPCON NORMAL | A general threat of terrorism exists; routine security posture |
| FPCON ALPHA | Increased general threat, not aimed at any particular installation |
| FPCON BRAVO | Increased and more predictable threat |
| FPCON CHARLIE | An incident has happened, or intelligence says some form of terrorist action is likely |
| FPCON DELTA | Attack in the immediate area, or intelligence says terrorist action against a specific location is imminent |
Each level comes with a set of measures: more ID checks, vehicle inspections, barriers, closed gates, restrictions on deliveries and visitors. At DELTA a base comes close to locking down.
Authority is layered. The secretary of defense sets policy through the chairman of the Joint Chiefs. Combatant commanders set minimum levels for their areas; for installations in the continental United States, that’s the commander of US Northern Command. Local commanders can raise the level for their own installation but can’t drop below the level directed from above without approval. FPCON DELTA was applied widely on 11 September 2001. Unlike DEFCON, FPCON changes at a given base are often visible from outside, because the gate queues get longer.
MOPP: chemical protection on the body
MOPP, Mission Oriented Protective Posture, is narrower and more physical. It tells troops which pieces of their chemical, biological, radiological and nuclear (CBRN) protective gear to wear and which to carry. The in-theatre commander usually sets it, based on the threat and on the job at hand.
| Level | Worn | Carried or ready |
|---|---|---|
| Mask only | Nothing | Mask carried |
| MOPP Ready | Nothing | Mask carried; first set of suit, gloves and boots available within two hours, second set within six |
| MOPP 0 | Nothing | Mask carried; suit, boots and gloves immediately available |
| MOPP 1 | Overgarment (suit) | Mask carried; boots and gloves immediately available |
| MOPP 2 | Suit and overboots | Mask and gloves carried |
| MOPP 3 | Suit, overboots and mask with hood | Gloves carried |
| MOPP 4 | Everything | Nothing left to put on |
The trade-off is heat and performance. MOPP 4 protects best but makes troops slower, harder to understand on the radio and prone to heat casualties. Commanders often order mixed postures, such as MOPP 2 with masks on, to fit the threat. The MOPP levels entry covers the gear and the 1991 Gulf War experience in more detail.
EMCON: controlling what you transmit
EMCON, emission control, is the odd one out: it is a discipline more than a threat-driven alert. It limits a unit’s electromagnetic emissions (radar, radio, datalinks, active sonar) so an enemy can’t find it with passive sensors. The commander sets it in the operation plan, and it can apply to a single ship, a carrier strike group or a ground headquarters.
There is no single public, joint DEFCON-style table for EMCON. Services and coalitions define their own conditions. A commonly cited naval scheme runs:
| Condition | Posture |
|---|---|
| EMCON DELTA | No restrictions; all emitters in use |
| EMCON CHARLIE | Emitters that reveal the ship’s class are restricted; mission-essential ones stay on |
| EMCON BRAVO | Most active emitters silenced; limited communications on set frequencies and times |
| EMCON ALPHA | Full silence; the unit receives but doesn’t transmit |
Practitioners describe it as a dimmer, not a switch. A ship in a busy sea lane needs navigation radar; a battalion needs some radio traffic. Choosing what to keep on is a tactical call. The EMCON entry has the Falklands example. Commercial shipping has its own version of going dark: switching off AIS transponders, a common tactic in sanctions evasion around chokepoints such as the Strait of Hormuz.
CPCON and INFOCON: the cyber scales
The Defense Department also has an alert scale for its networks. The older one, INFOCON (Information Operations Condition), ran from 5 (no unusual hostile activity) to 1 (active attack, network defense at maximum). It has given way to CPCON, the Cyberspace Protection Condition, established for the department by US Cyber Command instruction 5200-13.
CPCON also runs from 5 (very low threat) to 1 (very high). The design differs from the other scales: instead of adding protective layers everywhere, higher CPCON levels narrow the defensive focus to fewer, more important functions. At the top end, users should expect non-essential services to be cut or restricted so that critical functions stay up.
The scales side by side
| Scale | What it measures | Levels (low to high) | Who sets it | Public? |
|---|---|---|---|---|
| DEFCON | Readiness for war, including nuclear | 5, 4, 3, 2, 1 | President and secretary of defense via the chairman of the Joint Chiefs; can vary by command | No; historic changes became known later |
| FPCON | Terrorist threat to installations and people | NORMAL, ALPHA, BRAVO, CHARLIE, DELTA | Combatant commanders set minimums; local commanders may raise | Often visible at the gate |
| MOPP | CBRN protective gear worn | Mask only, Ready, 0, 1, 2, 3, 4 | Commander in theatre, by threat and task | Unit-level |
| EMCON | Electromagnetic emissions allowed | Service-specific; often DELTA (open) to ALPHA (silent) | Operational commander, in the plan | No; secrecy is the point |
| CPCON | Defensive posture of DoD networks | 5, 4, 3, 2, 1 | Under US Cyber Command policy | Felt by network users |
Reading alert news
A few habits help. Ask which scale. A headline about a base going to “Charlie” is about terrorism risk at that base and says nothing about nuclear readiness. Ask whose level, too. DEFCON and FPCON are set per command or per installation, so “US forces in Korea” and “US forces worldwide” are different stories. And be wary of numbers that weren’t announced. DEFCON changes are rarely confirmed at the time.
Alerts also come wrapped in reporting and orders. The SITREPs, SPOTREPs and FRAGOs that move up and down the chain when a level changes are covered in military reporting formats explained. For the alliance side, where a member under threat asks for consultations rather than raising a readiness number, see NATO Article 4 vs Article 5. And raised readiness never changes what force is lawful; that line is drawn in LOAC vs. ROE.