Intercontinental ballistic missile

An intercontinental ballistic missile (ICBM) is a land-based missile with a range in excess of 5500 kilometers.. "Ballistic" describes its trajectory, with a powered boost phase into space, midcourse coasting along a suborbital phase, and unpowered reentry at one or more points determined by a precision navigational system. ICBMs were one of the main weapon systems of the Cold War, with between 2000 and 3000 deployed by the U.S. and Soviet Union, and in the tens by China.

Of the strategic delivery systems of what been called the "Triad" of nuclear delivery systems, each presenting an adversary with a different defense problem:

• ICBMs
• Manned bombers, dropping gravity bombs and air-launched cruise missiles
• Submarines with submarine-launched ballistic missiles and cruise missiles

ICBMs are considered the most vulnerable, and their numbers have been considerably reduced both by bilateral arms control agreements between the U.S. and Russia. States of the former Soviet Union that had ICBM bases have shut them down. France and the United Kingdom have never deployed ICBMs, although they had shorter-ranged land-based ballistic missiles, nuclear weapons delivery aircraft, and submarines that launched nuclear missiles.

No other nation had demonstrated an operational ICBM capability, although nations with significant satellite launch capability clearly have missile technology that could be converted to ICBM applications. North Korea has threatened development one, but their tests have not indicated that they are close to operational status. In addition, practical ICBMs need compact thermonuclear warheads, which some countries with advanced rocket programs, such as Japan, do not have in their inventory.

Categories

ICBMs, variants of which are used as space launch vehicles, are categorized as "heavy" or "light". Heavy ICBMs have a total launch weight greater than 106,000 kilograms or a payload throw-weight greater than 4,350 kilograms. Heavier ICBMs can lift larger single reentry vehicles, as were needed for early high-yield thermonuclear bombs, or multiple reentry vehicles.

"First generation" ICBMs, such as the US Atlas (missile, required liquid fueling before they could be launched, a process taking hours and leaving the missile quite vulnerable. The second generation used either solid propellants or storable liquid propellants, and could be launched from a hardened silo. Third generation ICBMs were far more accurate, were capable of using multiple reentry vehicles, were even more accurate, and could be in even more hardened launch facilities.

Guidance and accuracy

Guidance most often uses inertial navigation, sensing accelerations and decelerations on the path away from a precisely surveyed launch point. Some also use celestial navigation, primarily before reentry, in which they determine their location based on the bearings to a set of stars. Certain early first-generation ICBMs also received guidance commands from their launch point, during the boost phase.

Payloads

ICBMs most commonly had nuclear warheads, although there are reports that some Soviet missiles may have had biological warheads. Several U.S. Minuteman ICBMs carried radio transmitters of the Emergency Rocket Communications System, which could send launch orders to other nuclear forces.

With the reduction of nuclear payloads through arms control, there is experimentation with the use of "kinetic kill" warheads for ballistic missiles. The kinetic energy of the reentry vehicle is so high that a conventional explosive warhead would not add as much energy as a dense inert mass.

Arms Control

There has been significant reduction, through arms control agreements, of ICBM rockets, and of their capabilities such as multiple independently targetable reentry vehicles (MIRV). Verification of compliance with the treaties involves national technical means of verification and bilateral on-site inspections and overflights by monitoring aircraft.