Precision-guided munitions (PGM) can trace their origins back to World War Two. These early weapons, such as the QB-17G "Aphrodite" were essentially airframes packed with explosives and guided via radio direction signals to their target, where they would crash and explode. While guidance was extremely crude by today's standards, these weapons were more accurate than conventional dropped munitions, and did not expose aircrews to deadly enemy anti-aircraft fire. Unfortunately, such weapons were unwieldy, unsuitable for small targets, and were themselves subject to defensive fire. The first truly precision-guided munitions did not appear until the Vietnam War. Serving as a major supply conduit for North Vietnam, the mile long Paul Doumer Bridge over the Red River was the most important ground target of the war. Unfortunately, it was also one of the most heavily defended, its approaches ringed with anti-aircraft guns and surface to air missile emplacements. While American pilots were able to attack the bridge using conventional munitions, such missions were extremely hazardous and casualties were high. In 1967 the Rockwell International Corporation was tasked with producing a precision munition using electro-optical guidance technology. The end result was the GBU (Guided Bomb Unit) 8 or Homing Bomb System (HOBOS), a conventional Mk. 84 2,000 pound bomb with a TV like electro-optical guidance package in the nose to provide direction and a modified tail fin assembly in the rear to provide lift. To launch the GBU-8 the pilot aligned the TV camera sight in the bomb with the target and the weapons officer locked the bomb's seeker onto the target. Once aligned, the bomb could be released well away from the target area and it would guide itself into the target with a high degree of accuracy.
GBU-24E/B, an Enhanced Paveway Laser Guided Bomb, is a precision-guided hardened target penetrator used to destroy hardened aircraft hangers and underground bunkers. It integrates a Global Positioning System and a ring laser gyro inertial measuring unit (IMU) to the already fielded GBU-24B/B ""Paveway III"" with the existing laser guidance. A new guidance and control unit has been modified to incorporate GPS electronics, GPS antenna, IMU and software for precision GPS/INS guidance. Testing of this system began in late 1999.