The Air Force's nuclear missiles have stood ready for war on short notice for more than 50 years. Americans tend to assume the missiles are safe, if they even remember they exist. But safety cannot be taken for granted.
President John F. Kennedy said the missiles represent "the most awesome destructive power that any nation or any man has ever conceived."
A look, in brief, at the missiles and their mission:
The Air Force operates just one type of land-based nuclear missile, the Minuteman 3. It is a class of weapon known as an intercontinental ballistic missile, or ICBM. The term refers to the fact that it has global reach. It is ballistic because its trajectory consists of three parts: powered flight from the ground through the Earth's atmosphere; free-flight through space; and re-entry until it hits its target.
The U.S. has 450 of the missiles, each with a single nuclear warhead attached. The missiles are guided to a target by a self-contained navigation system that uses motion and rotation sensors to track and update the missile's position and orientation.
Each Minuteman 3 missile is based in its own underground silo "hardened" with concrete to withstand an enemy nuclear strike. The silo is linked via communications cables to a launch control center, also underground.
At the heart of the ICBM force are the men and women who command the missiles. They are called missileers and are junior officers — lieutenants and captains, typically ages 22 to 27. Two missileers operate an underground launch control center, which is responsible for 10 missiles.
The missileers do 24-hour "alert" shifts, then hand off to a replacement crew. Because the missiles are meant to be ready for combat on short notice, the launch capsules are manned without interruption, 365 days a year.
The ICBM force is divided between three Air Force bases — Malmstrom in Montana, F.E. Warren in Wyoming and Minot in North Dakota. Each base operates 150 missiles, divided into three squadrons of 50 missiles each.
The launch silos are located no less than 3 miles from each other and from their launch control center to make the force more survivable in a nuclear attack.
The force is commanded by a two-star general who heads the 20th Air Force. He answers to a three-star general at Air Force Global Strike Command at Barksdale Air Force Base in Louisiana who is responsible not only for the ICBMs but also for the B-2 and B-52 bombers that have a nuclear mission as well.
The current fleet of Minuteman 3 missiles was first deployed in 1970, making them older than any of the officers entrusted with the keys to launch them.
They are the third generation of Minuteman missiles. The first generation went into service in October 1962 during the Cuban missile crisis. The Minuteman 2 became operational in 1966, and the current version was declared operational at Minot in December 1970, according to an official Air Force history of the ICBM.
No ICBM has ever been launched other than for testing. The only time a nuclear weapon has been used in war was in August 1945 when the U.S. dropped one bomb on Hiroshima, Japan, and another on Nagasaki, compelling Japan's surrender.
The Obama administration has decided to take 50 of the 450 Minuteman missiles off active duty by February 2018, but it is committed to preserving their role as part of the "triad" of strategic nuclear forces, along with bombers and nuclear-armed submarines.
Because the missiles have long exceeded their original 10-year life expectancy and are in need of modernization, the Air Force is in the early stages of planning a series of further upgrades to keep the weapon system functioning for at least another 40 years.