Missiles that spend most of their flight falling through the air without power are called ballistic missiles. A rocket launches them high in the air, or even into space, and then gravity pulls them back down to the ground again. A tracking system finds the target and locks onto it. The tracking system gives the target’s location to the missile’s guidance system, which then works out the flight path the missile needs to follow. The guidance system commands the flight system to steer the missile, usually by moving fins on the missile’s body.
Small ballistic missiles are mounted on mobile launchers that can be moved from place to place. The biggest ballistic missiles—intercontinental ballistic missiles (ICBMs)-can fly more than 3,300 miles (5,300 kilometers) from one continent to another. These missiles are too big and heavy to be moved around by trucks, but they would be easy to attack if they stood out in the open. One way to hide large missiles from enemies is to keep them in launch tubes, called silos, buried in the ground. As missiles have become more accurate and more powerful, however, silos provide less protection. Another way to protect missiles
from enemy attack is to put them in nuclear submarines, which can stay submerged in the ocean for weeks at a time.