Fire-and-forget is a third-generation method of missile guidance. The military use the term for a type of missile which does not require further guidance after launch such as illumination of the target, and can hit its target without the launcher being in line of sight of the target. This is an important property for a projectile to have, since a person or vehicle that lingers near the target to guide the missile (using, for instance, a laser designator) is vulnerable to attack and unable to carry out other tasks.
Generally, information about the target is programmed into the missile just prior to launch. This can include coordinates, radar measurements (including velocity), or an IR image of the target. After it is fired, the missile guides itself by some combination of gyroscopes and accelerometers, GPS, organic RADAR, and infrared optics. Some systems offer the option of either continued input from the launch platform or fire-and-forget.
