Fire-and-forget is a third-generation method of missile

Missile

Though a missile may be any thrown or launched object, it colloquially almost always refers to a self-propelled guided weapon system.-Etymology:The word missile comes from the Latin verb mittere, meaning "to send"...

 guidance. The military uses the term for a type of missile which does not require further guidance after launch such as illumination of the target or wire guidance

Wire-guided missile

A wire-guided missile is a missile that is guided by signals sent to it via thin wires connected between the missile and its guidance mechanism, which is located somewhere near the launch site. As the missile flies, the wires are reeled out behind it...

 (TOW), and can hit its target without the launcher being in line-of-sight of the target. This is an important property for a guided weapon to have, since a person or vehicle that lingers near the target to guide the missile (using, for instance, a laser designator

Laser designator

A laser designator is a laser light source which is used to designate a target. Laser designators provide targeting for laser guided bombs, missiles, or precision artillery munitions, such as the Paveway series of bombs, Lockheed-Martin's Hellfire, or the Copperhead round, respectively.When a...

) 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

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

, and infrared optics. Some systems offer the option of either continued input from the launch platform or fire-and-forget.

Anti-Tank Guided Missiles (ATGMs) are guided to the target by multiple means, such as SACLOS

SACLOS

SACLOS is an acronym for Semi-Automatic Command to Line of Sight, a second-generation method of missile guidance. In SACLOS, the operator has to continually point a sighting device at the target while the missile is in flight...

 and MCLOS

MCLOS

MCLOS is a first-generation method for guiding guided missiles.With an MCLOS missile, the operator must track the missile and the target simultaneously and guide the missile to the target. Typically the missile is steered with a joystick, and its path is observed through a periscope-type...

. Laser designators/range finders are also used to designate the target for the missile to hit. But fire-and-forget missiles also have the tendency to be deflected by soft-kill systems on modern main battle tanks as well as also getting destroyed by hard-kill systems. As opposed to unguided RPGs which require a hard-kill system (a counter projectile(s) used to destroy the incoming missile), fire-and-forget missiles can be jammed by electro-optical dazzlers.

Examples

Many of these are infrared homing

Infrared homing

Infrared homing refers to a passive missile guidance system which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track and follow it. Missiles which use infrared seeking are often referred to as "heat-seekers", since infrared is just below the...

missiles; some of the remainder (e.g. AIM-54) are active radar guided.