When America's Strategic Air Command is ordered to Defense Condition 3 (DEFCON 3) or above, it disperses its nuclear bombers fully-armed across the U.S. and certain allied countries so that the bombers are harder to target. This keeps America's second strike capability intact and hopefully deters an enemy from launching its own nuclear weapons.
The dispersal plan generally calls for the planes to go to Air Force bases rather than civilian airports, but it hinges on a few factors. First, there have to be enough Air Force bases ready to receive the planes and the bases can't be needed for other missions.
During the Cuban missile crisis, SAC was ordered to DEFCON 3 and carried out its dispersal plan Oct. 22, 1962. Bases in and near Florida were mostly blocked off because they were needed to host troops for a potential invasion of Cuba. Also, they would have been destroyed too quickly in an attack for a crew to attempt to take off. So 183 nuclear-armed aircraft were sent to 33 military bases and civilian airports in the U.S., including the four civilian airports below.
Mitchell Field in Milwaukee, Wisconsin
Local pop. in 1960: 741,324
Four bombers were sent to Mitchell Field. One of the co-pilots on the flight told a reporter years later that the crew was ordered to fly for at least four hours to ensure their flight pay would be protected in case they couldn't get training flights for a while. Since they arrived at Mitchell Field in under four hours, the pilots flew a holding pattern for a few hours over Milwaukee in inclement weather at a lower altitude than their planes were designed to optimally fly while fully armed with nuclear weapons.
Logan Airport in Boston, Massachusetts
Local pop. in 1960: 697,197
When the B-47s arrived at Logan Airport, they found that the fuel plan wasn't ready to go. A lieutenant colonel had to buy fuel from a local Mobil station with his personal credit card. When the pilots went to check on their planes in the morning, they found that the jets had sunk into the soft concrete and had to be pulled out with a tow truck, according to Michael Dobbs in his book, "One Minute to Midnight."
Memphis Airport in Memphis, Tennessee
Local pop. in 1960: 497,524
Planes at the airport were filmed on the tarmac on Oct. 26, 1962. SAC had been upgraded to DEFCON 2 at this point, meaning they expected nuclear war to pop off at any moment and they had to be prepared to get all of the bombers into the air within 15 minutes of an alert.
Duluth Municipal Airport in Duluth, Minnesota
Local pop. in 1960: 106,884
Duluth Municipal Airport hosted eight bombers during the crisis.