PAVEWAY laser guidance
PAVEWAY laser guidance is a three-generation family of technologies, and associated tactics, for U.S. laser-guided bombs (LGB), which were the first modern precision-guided munitions. Like the Joint Direct Attack Munition, PAVEWAY is a set of components that attaches to a conventional unguided bomb. A fourth-generation PAVEWAY IV variant is in use by the Royal Air Force, but the U.S. has not decided if it will use it.
PAVEWAY I began development in 1965, but had a significant combat entry in 1972, causing rethinking of air tactics worldwide. PAVEWAY II, an incremental improvement with cost reductions, was responsible for the dramatic "video game" precision attacks of the Gulf War. PAVEWAY III, however, was a major redesign that, at increased cost, greatly increased the tactical utility of the weapons.
Laser guidance is a short-range technique for providing terminal guidance to hit a target that reflects the radiation of a laser designator. The designator can be in the air or on land, but must remain in line-of-sight with the target. The delivery aircraft, however, can release the bomb and turn away, as long as the bomb acquires the laser spot.
The initial program began in 1965, as a joint effort between the U.S. Air Force and Texas Instruments. They are best known for destroying the Dragon's Jaw bridge in North Vietnam in 1972, a target that had proved nearly invulnerable to unguided bombs. The earliest PAVEWAY I used aerodynamic control surfaces on the nose only, for both lift and control, but fixed rear "wings" were added to increase the glide range. 
Both the PAVEWAY I and II used "bang-bang control", in which a control surface is either fully deflected or not deflected at all.
Cost reductions in PAVEWAY II included the replacement of a number of metal parts with injection-molded plastic. Rather than being fixed at launch, the wings "popped out" after release, which enabled them to be carried more easily by the aircraft. While the electronic control was not truly programmable, individual bombs could be coded to respond to specific laser designators, allowing there to be multiple bombs airborne to multiple targets. Incremental improvements included a wider field of view in the laser seeker, and greater deflection on the control surfaces, allowing a wider range of attack geometries.
Improvements in the PAVEWAY II Plus are in the electronic guidance system.
While the best-known images were of bombs going through air shafts and windows to destroy key buildings, the most common use, in the Gulf War, was "tank plinking". Tanks, of course, are inherently hard targets, especially when partially buried in sand to make them hard to see. Aircraft with infrared viewers, however, could detect the difference in heat between a tank and the sand, and send an approximately $10,000 bomb against a tank costing between $500,000 and $1.5 million.
Enhanced Laser Guided Training Round
This variant contains no explosive. While it was intended for training, it has been used in combat against targets where collateral damage is of critical concern, and the kinetic energy of an inert bomb, striking from high altitude, is sufficient to disable the target.
Dual Mode Guided Bomb
Dual Mode PAVEWAY II kits add inertial guidance with Global Positioning System updating, to provide midcourse guidance to complement the laser terminal guidance. Midcourse guidance extends the standoff range of the bomb.
With a much more sophisticated true control computer, which allows proportional aerodynamic control to replace bang-bang control, the PAVEWAY III is far less sensitive to the delivery altitude and geometry than the PAVEWAY II. Its larger wings give it both more maneuverability and longer standoff range.
It is considerably more expensive than the PAVEWAY II, so both II and III versions will remain in service.
The principal PAVEWAY III is the GBU-24, a 2000 pound hard target penetrator used by the U.S. and U.K.
Larger penetrators, such as the 5000 pound class GBU-28, also are in service. The original GBU-28 was built during the Gulf War as a "bunker buster" for targets invulnerable to the 2000 pound bombs. Its first version was made from bored-out howitzer barrels, and carried by F-111 aircraft. Production versions now have purpose-built penetrator cases, and are carried by the F-15E Strike Eagle and the B-2 Spirit.
While the U.S. has not put it into service, and its needs may be met by the Joint Direct Action Munition (JDAM) and its GBU-38 and GBU-53 Small Diameter Bomb variants, the PAVEWAY IV was developed for the Royal Air Force, replacing "existing Paveway II and Enhanced Paveway II weapons and 505kg unguided general purpose bombs" with a smaller warhead. Like the U.S. Small Diameter Bombs, an aircraft can carry more weapons while reducing collateral damage.
Convergence with other technologies
Joint Direct Attack Munitions (JDAM) are also strap-on guidance kits, using satellite-updated inertial navigation for midcourse guidance that extends into the terminal phase of flight. Certain JDAM variants, such as the GBU-54, are supplemented with laser terminal guidance. They do have longer range than the PAVEWAY, but the capabilities obviously are converging. Inertial and GPS guidance still gets the JDAM to the target area (i.e., midcourse guidance), but it then follows a laser designator spot onto a potentially moving target.
The GBU-54 has been tested on F-16 Fighting Falcon and now B-52 aircraft, and began used operationally in Iraq in 2008.  Note that it does not have the large wings of a PAVEWAY, and is intended for medium to high altitude delivery, but at much longer range than PAVEWAY weapons.
In development is the second-generation GBU-53 Small Diameter Bomb, which adds the Common Tri-Mode Seeker (CMTS) to the standard inertial and GPS, providing laser, imaging infrared, and radar guidance. It also has a unique explosive filler; the GBU-53 is not an add-on kit to an existing bomb, but still reuses JDAM technology.
- Carlo Kopp (September, 1981 (updated 2005)), "Laser Guidance", Australian Aviation & Defence Review
- Carlo Kopp (November, 2010), "The GBU-28 Bunker Buster", Air Power Australia, Technical Report APA-TR-2005-0501
- Paveway IV, Royal Air Force
- Air Force Link (August 27, 2008), Airmen employ laser joint direct attack munition in Iraq