The main appeal of using an energy beam to shoot things is that it travels at the speed of light, which means, in practice, that it will hit whatever it is aimed at. Trying to shoot down an incoming missile or warhead with a physical projectile, by contrast, is much more difficult. The guidance challenges of trying to “hit a bullet with a bullet” are enormous and are only gradually being solved using complex radars and missiles equipped with expensive sensors. A second attraction of lasers and other energy weapons is that in most cases they cannot run out of ammunition, and can keep firing for as long as they are plugged into a power source. The initial costs may be quite high, but each shot may then cost only a few dollars, compared with a price-tag of $3m or more for the latest missiles used to shoot down aircraft or other missiles.
Yet until very recently, despite the billions of dollars invested in them, military lasers have had a less than glowing record/.../The Center for Strategic and Budgetary Assessments, a think-tank based in Washington, DC, argues that various sorts of solid-state lasers could be in service on American ships by 2018. It thinks that they could also be used to counter cruise missiles flying directly at a ship, using relay mirrors mounted on nearby unmanned aircraft.