What Are Intercontinental Ballistic Missiles and How Many Does Russia Have?

The U.S. postponed a planned intercontinental ballistic missile (ICBM) test on Wednesday in a bid to cool rising tensions with Russia.

The move came after Russian President Vladimir Putin ordered the country to put its nuclear weapon systems into "special alert" on Sunday as it faces global backlash over its ongoing invasion of Ukraine.

The world has not seen the use of a nuclear weapon in wartime since World War II, when the U.S. bombed Hiroshima and Nagasaki, Japan, in 1945.

Countries generally seek to avoid their use due to the widespread destruction that nuclear weapons cause, but several maintain active nuclear deterrents—nuclear weapons systems intended to put other countries off of using their own systems due to the threat of mutual catastrophe.

Nuclear weapons in the form of warheads are typically delivered by an ICBM—a large missile capable of traveling around 15,000 miles per hour.

When ICBMs are launched, they travel high above the Earth's atmosphere, where they will travel for a given amount of time before falling back to Earth to their intended target.

Traveling in this way at high speed gives ICBMS a much larger range than other types of missile, hence the word 'intercontinental' in the name. Some can travel close to 10,000 miles. In physics and mathematics, the word 'ballistic' refers to the motion of projectiles.

ICBMs have three stages of flight: a three-to-five-minute boost phase in which the missile's rocket engine fires it up through the atmosphere; a midcourse phase, which varies in time but can last around 20 minutes, in which the rocket engine stops and the missile continues to ascend until the highest point in its trajectory and then begins to descend; and a terminal phase which can last less than one minute, in which the missile's detached warheads re-enter Earth's atmosphere.

Estimates on nuclear warheads and ICBMs held by each country vary.

According to a fact sheet by the U.S. Bureau of Arms Control, Verification and Compliance published in September, 2021, the U.S. has 665 deployed ICBMs, including ones launched from submarines and deployed heavy bombers, while Russia has 527.

These numbers are based on ICBMs declared by the U.S. and Russia under the New START Treaty to reduce the number of nuclear arms held by each.

Each ICBM has the potential to carry multiple nuclear warheads. As of February 2022 the Bulletin of the Atomic Scientists estimated that Russia has a stockpile of nearly 4,500 nuclear warheads, of which around 1,400 are deployed on ICBMs.

According to the Federation of American Scientists, both Russia and the U.S. each have "around 4,000" stockpiled nuclear warheads—around 90 percent of the world's total.