A high-alert nuclear weapon commonly refers to a launch-ready ballistic missile that is armed with a nuclear warhead whose launch can be ordered (through the National Command Authority) and executed (via a nuclear command and control system) within 15 minutes. It can include any weapon system capable of delivering a nuclear warhead in this time frame.

Virtually all high-alert nuclear weapons are possessed by the United States and Russia.^[1] Both nations use automated command-and-control systems, in conjunction with their early warning radar and/or satellites, to facilitate the rapid launch of their land-based intercontinental ballistic missiles (ICBMs) and some submarine-launched ballistic missiles (SLBMs).^[2] Fear of a "disarming" nuclear first strike, which would destroy their command and control systems and nuclear forces, led both nations to develop "launch-on-warning" capability, which requires high-alert nuclear weapons that can launch within 30 minutes of a tactical warning, the nominal flight time of ICBMs traveling between both countries.

A definition of "high-alert" requires no specific explosive power of the weapon carried by the missile or weapon system, but in general, most high-alert missiles are armed with strategic nuclear weapons with yields equal to or greater than 100 kilotons.^[3] The United States^[4] and Russia^[5] have for decades possessed ICBMs and SLBMs that can be launched in only a few minutes.

The U.S. and Russia as of 2008 have a total of 900 missiles and 2581 strategic nuclear warheads on high-alert launch-ready status. The total explosive power of the weapons is about 1185 megatons, or the equivalent explosive power of 1.185 billion tons of TNT.^[6]