In military language, a missile, also known as a guided missile, is a guided self-propelled flying weapon usually propelled by a jet engine or rocket motor.
This is in contrast to an unguided self-propelled flying munition, referred to as a rocket (although these too can also be guided). Missiles have four system components: targeting or missile guidance, flight system, engine, and warhead.
Missiles come in types adapted for different purposes: surface-to-surface and air-to-surface missiles (ballistic, cruise, anti-ship, anti-tank, etc.), surface-to-air missiles (and anti-ballistic), air-to-air missiles, and anti-satellite weapons.
Non-self-propelled airborne explosive devices are generally referred to as shells and usually have a shorter range than missiles. In ordinary language the word means an object which can be thrown, shot, or propelled toward a target.
The first missiles to be used operationally were a series of missiles developed by Nazi Germany in World War II. Most famous of these are the V-1 flying bomb and V-2 rocket, both of which used a simple mechanical autopilot to keep the missile flying along a pre-chosen route. Less well known were a series of anti-shipping and anti-aircraft missiles, typically based on a simple radio control (command guidance) system directed by the operator. However, these early systems in World War II were only built in small numbers.
Missile Maintainer inspects missile guidance system of the LGM-30G Minuteman ICBM
The most common method of guidance is to use some form of radiation, such as infrared, lasers or radio waves, to guide the missile onto its target.
This radiation may emanate from the target (such as the heat of an engine or the radio waves from an enemy radar), it may be provided by the missile itself (such as a radar), or it may be provided by a friendly third party (such as the radar of the launch vehicle/platform, or a laser designator operated by friendly infantry).
The first two are often known as fire-and-forget as they need no further support or control from the launch vehicle/platform in order to function.
Another method is to use a TV guidance, with a visible light or infrared picture produced in order to see the target. The picture may be used either by a human operator who steering the missile onto its target or by a computer doing much the same job.
One of the more bizarre guidance methods instead used a pigeon to steer a missile to its target. Some missiles also have a home-on-jam capability to guide itself to a radar-emitting source.
Many missiles use a combination of two or more of the methods to improve accuracy and the chances of a successful engagement.