DEFCON levels are set by the Joint Chiefs of Staff and are not necessarily consistent across military branches. Although the official DEFCON level is not available to the public, unofficial (but historically accurate) DEFCON levels are reported a day or so later at defconlevel.com.

DEFCON levels range from 1 to 5, designed to correspond to situations where there is a possibility of military action against the U. S. or our allies. Here’s a breakdown of what the different levels entail, according to the Department of Defense Dictionary of Military and Associated Terms

DEFCON 5: Normal, lowest state of readiness.

DEFCON 4: Regional tensions requiring greater vigilance; no U.S. force involvement. Increased intelligence watch and analysis of the political/military situation in the area of tension.

DEFCON 3: Increased regional tensions with possible U.S. force involvement. Increase in force readiness.

DEFCON 2: Hostile action is possible; serious threat to U.S. forces or U.S. allies. Further increase in force readiness.

DEFCON 1: War is imminent. Maximum readiness, immediate response.

Since the DEFCON system was invented in 1959, there have never been any DEFCON 1 declarations. Here are some instances of what the DECFON levels actually look like in practice:

The first time the DEFCON level was raised to 2 was during the Cuban missile crisis in 1962.

Following the attacks on Sept. 11, 2001, the U.S. entered DEFCON 3. It was lowered to DEFCON 4 three days later on Sept. 14.

Currently, the U.S. is at DEFCON 3 due to the conflict between Russia and Ukraine.