A
cruise missile is, essentially, an unpiloted
kamikaze aircraft. All cruise missiles use small wings to generate lift, and maneuver just as an aircraft does. Most actually use control surfaces. In any case, they can be propelled by various means, the most popular being a
jet engine of some sort, although
rockets work for short ranges.
While one can of course create roughly the same effect more easily by having a remote human fly the device, this is a fundamentally different thing. Such devices are called drones rather than cruise missiles, since 'missile' implies that constant input is not required for the device to hit its present target. Remote targeting updates are not the same; those simply change the weapon's desired point of impact rather than provide control inputs necessary for flight. Reliance on communications to and from the pilot's 'base station' elsewhere mean that the weapon can be countered via electronic means without actually engaging the weapon itself - whereas a cruise missile can, typically, remain independent once launched.
These are not 'hard and fast' terminology differences, however. A drone designed to kamikaze, with some minimal autopilot capabilities, is in effect a cruise missile - if the user doesn't care too much about where it lands.
Although the US Tomahawk may be the most popular example in use currently, probably the best known cruise missile is one of the originals - the V-1, also known to the Germans as the Fieseler and to the British as the buzz-bomb.
A cruise missile differs from a regular missile in that it is designed to reach its target through continuously powered and controlled flight (although there may be some unpowered gliding near the end of its run). There are several advantages to this:
- Stealth. A cruise missile, remaining low to the ground and not rising above the horizon, is very very difficult to detect. You need to use either look-down radar or aircraft spotters, generally.
- Cost. Although they're not cheap (Tomahawks run between $500K and $1.2 million depending on version), they are a much cheaper means of getting a payload out to those distances than a ballistic missile.
- Risk. You don't have to put a human pilot in one, so you can essentially bomb things without worrying about losing people. This is important if you (like the U.S.) worry about this to an obsessive level.
Of course, some of these are disadvantages as well. The lack of a human pilot and the kamikaze nature means you can't re-use the thing, whereas you can (hopefully!) get multiple missions out of a piloted aircraft. While they'e cheaper than ballistic missiles, they're more expensive than the gravity bombs you'd drop from a manned aircraft. Finally, their low and slow flight means they can be engaged by a much wider variety of systems, including MANPADS and SAMs, with consequently less chance of reaching target. Of course, since they're cheaper than ballistics, you can buy more...and so on, and so on.