Intercontinental ballistic missile

An Intercontinental Ballistic Missile (often abbreviated ICBM) is a weapons system that has played a role in one form or another in the various Fallout games, for example as a world object in the Fallout: New Vegas add-on Lonesome Road and in Fallout 76. ICBMs mentioned/encountered in the overall game universe include the Minuteman XI and the Titan V, both originally operated by the pre-War United States Air Force.

Background
The ICBM is a ballistic missile with a long range typically designed to deliver a nuclear payload (usually one or more nuclear warheads). The missile launches up into low orbit, where it can then deploy one or more nuclear warheads on almost any location on the planet. They could be fitted with a variety of payloads, ranging from high explosive to biowarfare loadouts, but the most common were nuclear warheads. A typical single warhead ICBM has a blast radius of several miles, and a fallout range of even further, depending on the explosive yield the warhead contains.

ICBMs can be launched from hardened (sometimes hidden) missile silos, or alternatively from mobile ground launch platforms such as missile trains and tracked or wheeled Transporter erector launcher (TEL) vehicles. In addition, during the Cold War there were successful experiments in launching them from aircraft by first air-dropping them and then triggering their ignition sequences in mid air.

Fallout 3
ICBM silos can be found throughout the Capital Wasteland. An ICBM launch terminal, launch codes, and facility can be found at Fort Constantine. The launch codes are for a Minuteman XI missile.

The Delta IX rocket fleet, while not originally designed and built as ICBMs, were (somewhat crudely) converted into such around the year 2034. One such example that was presumably fired against China on the outbreak of the Great War failed shortly after launch, crashing just outside the Statesman Hotel in Washington, D.C. where it can still be found as of 2277.

Fallout: New Vegas
Raul Tejada recalls seeing Mr. House's anti-missile defense systems shoot down Chinese ICBMs during his unmarked quest Old School Ghoul.

ICBMs can also be seen throughout the Divide, stationary and while in flight before detonating, and their warheads can also be seen and detonated.

Fallout 4
Pre-War, at the USAF's Sentinel Site Prescott located to the Southwest of Boston, developmental work was underway on an unidentified 'heavy' ICBM intended to allow it to deliver multiple Mark 28 bombs (originally designed to be air dropped from strategic bombers) against a target. The missile itself is not seen in-game however.

Fallout 76
ICBMs play a large role in the main story of Fallout 76, as Vault 76's overseer has disappeared while attempting to track down and secure the three missile silos hidden around Appalachia. Fallout 76 is also the second game in the Fallout series where player characters can launch ICBMs, however unlike in New Vegas the player character has to track down the launch code, and can aim where the warhead is going to go to a greater extent.

Behind the scenes
The general design of most of the ICBMs seen in Lonesome Road resembles a combination of the SM-65 Atlas and the LGM-25 Titan-II. This particular design appears to be designated as "Titan V," likely a Star Trek Easter egg. Other missiles encountered seem to be Minuteman XIs.