A laser-guided bomb (LGB) is a guided bomb that uses semi-active laser guidance to strike a designated target with greater accuracy than an unguided bomb. First developed by the United States during the Vietnam War, laser-guided bombs quickly proved their value in precision strikes of difficult point targets. These weapons use on-board electronics to track targets that are designated by laser, typically in the infrared spectrum, and adjust their glide path to precisely strike the target. Since the weapon is tracking a light signature, not the object itself, the target must be illuminated from a separate source, either by ground forces, by a pod on the attacking aircraft, or by a separate support aircraft. Data from Vietnam showed that laser-guided bombs achieved direct hits nearly 50% of the time, versus just 5.5% for unguided bombs. Because of this dramatically higher precision, laser-guided munitions can carry less explosive and cause less collateral damage than unguided munitions. Today, laser-guided bombs are one of the most common and widespread guided bombs, used by a large number of the world's air forces.
Laser-guided weapons were first developed in the United Kingdom and United States in the early 1960s. The United States Air Force issued the first development contracts in 1964, leading to the development of the Paveway series, which was used operationally in the Vietnam War starting in 1968. Although there were a variety of technical and operational problems, the results were generally positive. LGBs proved to offer a much higher degree of accuracy than unguided weapons, but without the expense, complexity, and limitations of guided air-to-ground missiles like the AGM-12 Bullpup. The LGB proved particularly effective against difficult fixed targets like bridges, which previously had required huge loads of "dumb" ordnance to destroy.
It was determined that 48% of Paveways dropped during 1972–73 around Hanoi and Haiphong achieved direct hits, compared with only 5.5% of unguided bombs dropped on the same area a few years earlier. The average Paveway landed within 23 feet of its target, as opposed to 447 feet for gravity bombs. The leap in accuracy brought about primarily by laser guidance made it possible to take out heavily defended, point objectives that had eluded earlier air raids.
The most dramatic example was the Thanh Hoa Bridge, 70 miles south of Hanoi, a critical crossing point over the Red River. Starting in 1965, U.S. pilots had flown 871 sorties against it, losing 11 planes without managing to put it out of commission. In 1972 the “Dragon’s Jaw” bridge was attacked with Paveway bombs, and 14 jets managed to do what the previous 871 had not: drop the span, and cut a critical North Vietnamese supply artery.
In the wake of this success, other nations, specifically the Soviet Union, France, and Great Britain, began developing similar weapons in the late 1960s and early 1970s, while US weapons were refined based on combat experience.
The United States Air Force and other air forces are now seeking to upgrade their LGBs with GPS guidance as a back-up. These weapons, such as the USAF Enhanced Guided Bomb Unit (part of the Paveway family), use laser designation for precision attacks, but contain an inertial navigation system with GPS receiver for back-up, so that if the target illumination is lost or broken, the weapon will continue to home in on the GPS coordinates of the original target.