DEFCON: Here’s how the US decides to launch nukes

"I was so pissed off I went to DEFCON 5" or a similar phrase in the lexicon means you are at the highest level of anger, but it doesn't make any sense when you explore what DEFCON really means.

DEFCON, the shortened-version of "Defense Readiness Condition," is a five-level scale of alert status that the U.S. uses to determine nuclear readiness. In essence, the number next to DEFCON tells everyone how close we are to getting into a nuclear shooting war.

The need for DEFCON came from the Cold War. In 1958, with the U.S. pointing all of its nukes at Moscow — and Russia doing exactly the same back at Washington — the Air Force created the North American Aerospace Defense Command (NORAD) to provide early warning and defense against nuclear threats.

Though it has somewhat changed over time, the DEFCON system was proposed by NORAD in 1959. It created a system of "five different alert levels with detailed, if ambiguous, descriptions and expected actions by military forces at each threat level," according to the Encyclopedia of the Cold War.

The levels are primarily used by the Joint Chiefs of Staff or commanders of joint commands, and can be in force military-wide, though they are usually only applied to specific units. But unlike the saying of "going to DEFCON 5," the worst possibility is at level one.

There are five levels, which signify varying conditions of readiness. They are:

DEFCON 5: Normal peacetime readiness. All is calm, the skies are blue, and we aren't even thinking about nukes.

DEFCON 4: Above normal readiness. The U.S. slightly increases intelligence and strengthens security measures.

DEFCON 3: Air Force ready to mobilize in 15 minutes. There's an increase in force readiness above normal readiness and things are heating up. Troops start fueling up missiles and bomber crews are getting ready.

DEFCON 2: Air Force is ready to deploy and engage in less than six hours. Things are getting really serious and we are one step away from pushing the button. The missiles are ready to go and waiting on the order, and bomber crews are in the air near their targets.

DEFCON 1: Maximum readiness. Nuclear war is imminent, so you should probably get into the bunker.

Nope, but we came pretty close.

During the Cuban Missile Crisis, U.S. Strategic Air Command was placed at DEFCON 2 while the rest of the military was at DEFCON 3. What that meant for military units: On Oct. 22, 1962 SAC ordered its B-52 bombers on airborne alert. Then as tension grew over the next day, SAC was ordered to remain ready to strike targets inside of the Soviet Union.

"Pilots flew these nuclear laden airborne alerts, commonly known as Chrome Dome missions, for 24 hours before another air crew assumed the same flight route," wrote Air Force journalist Stephanie Ritter. "Chrome Dome ensured that a percentage of SAC bombers could survive an enemy surprise attack and that the U.S. could retaliate against the Soviets. At the height of the air alerts, SAC produced 75 B-52 sorties a day."

In addition to the flying sorties, more than 100 intercontinental ballistic missiles were placed on alert, waiting for the president's order to launch. Luckily that didn't happen.

U.S. forces were brought back to DEFCON 4 on Nov. 20, 1962. Though it has been placed at DEFCON 3 a few other times, the only known readiness level of 2 was during the missile crisis.