The usefulness of precision weapons, particularly those that depend on a sensor that detects and homes in on reflected laser light, has depended on gradual improvements on a technology first used on precision bombs in the 1960s. For example, the most recent advances have produced a laser seeker that is lighter (350 g/12.3 ounces), smaller (52mm in diameter), more reliable and more sensitive. This last item is particularly important because laser guided bombs and missiles are expected to reliable go after moving targets. The latest generation of laser seekers can do that. Not only that but these new sensors are small enough to fit on new, smaller, guided missiles like those based on World War II era 70mm rockets.
This comes after the recent (2008) introduction of a new generation of laser seekers that many heretofore difficult shots possible while increasing the overall success of missiles fired to over 90 percent. The main breakthrough here was producing a sensor able to spot the reflected laser light within a 180 degree arc, rather than 40 degrees as before. Not easy, from a technical point of view, but it's a technique that has worked well in other missile types.
The way hellfire and other laser guided missiles work is that you have someone (in the air or on the ground using a laser designator) shine a laser light (think of a tiny, long range, laser spotlight) on the target. The invisible light bounces off the target, providing a target for the laser seeker in the front of the missile. Thus you have to fire the missile in the direction of the "illuminated" target, and hope that the seeker picks up the reflected light. The homing part is easy. Getting the rapidly moving missile to where its sensor can pick up the reflected laser light can be tricky. One of the first uses of these new sensors was in the "P" model of the Hellfire laser seeker. This allowed Hellfires to be fired from higher altitudes and even when the aircraft has passed the target area. Users were quick to report increased success because of the new seeker and manufacturers realized that even more improvements were possible.
The new, smaller sensors are particularly useful in the smaller and cheaper guided missiles entering service. For example the new 70mm guided missile costs about $30,000 each. This is typical for these smaller weapons and about a third less than a smart bomb and less than a third of what a Hellfire missile costs.
The guided 70mm rocket is used against targets that doesn't require a larger (49 kg/108 pound), and more expensive (over $100,000) Hellfire missile but still needs some targeting precision. In tests the 70mm missile hit within a meter (a few feet) of the aiming point, about what other laser guided missiles are capable of. The 70mm missile makes an excellent weapon for UAVs, especially since you can carry more of them. The launcher for carrying these missiles is designed to replace the one for Hellfire but can carry four missiles instead of one.
All these 70mm guided rockets are basically 13.6 kg (30 pound) 70mm rockets with a laser seeker, a 2.7 kg (six pound) warhead, and a range of about six kilometers when fired from the air. Laser designators on a helicopter, or with troops on the ground, are pointed at the target and the laser seeker in the front of the missile homes in on the reflected laser light.