Fighter Wing: A Guided Tour of an Air Force Combat Wing

Electro-Optical Bombs: The GBU-15/AGM-130 Series

Airpower enthusiasts have long dreamed of a munition which would drop a bridge or destroy a building with only one round. This has been the promise of airpower for over seventy-five years, and it has taken a long time to even get close to that. Like the AAM, the first real successes in the area of precision-guided munitions came from Nazi Germany in World War II. In 1943, the Luftwaffe deployed a pair of guided bombs, the FRITZ-X and the HS-293, for use as standoff precision strike weapons. Though they were quite primitive, they terrorized Allied shipping, and even sank an Italian battleship, the Roma, as it was on its way to surrender to Allied forces. After World War II, such efforts took a backseat to nuclear weapons development. Then, with the coming of the Vietnam War, the Air Force was forced to realize that there were a number of international situations where nukes were just not appropriate. Thus, the USAF went into Vietnam completely unequipped for the war they would spend the next decade trying to win.

Immediately, the air units involved in the war began to find that they had been the victims of an unanticipated paradigm shift. Where in the past the flattening of a town with a carpet of GP bombs was a politically acceptable option, in Vietnam, it was a war crime. The politics of appearance were taking over in the 1960s, with the result that politicians now wanted the 'surgical' air strikes that airpower zealots had promised for decades. Unfortunately, such promises by the visionaries who had created airpower as a weapon had never anticipated flying into an integrated air defense system (IADS) of fighters, SAMs, and AAA guns all tied together with a computerized sensor network of radars and observation posts. No one had anticipated that crews of tactical aircraft would be trying to drop their loads of munitions while violently 'jinking' and fighting for their lives against coordinated multiple threats such as American pilots and crews saw in the skies over North Vietnam. Worse than that was where some of those bombs fell after they were dropped. Collateral damage is a serious concern in any war, but even more so when the enemy is showing American newsmen the destruction wrought by errant bombs and contrasting it with the stories of 'precision strikes' coming out of official channels in Washington, D.C.

In an effort to overcome the political problems of collateral damage, as well as the tactical problems of fighting in an IADS environment to precisely deliver ordnance onto a target, the USN and USAF initiated a series of programs known as Precision Avionics Vectoring Equipment (PAVE), designed to provide aviators with weapons that could hit high-value targets with some sort of standoff and precision. One promising technology was television electro-optics (TV E/O). This means that the guidance electronics package looks at the TV camera picture and locks onto the contrast 'edge' or line between a dark and light zone on the picture. Integrated circuits and microprocessors were years away, and the early history of what we now call electro-optically (E/O) guided bombs was riddled with problems as a result.

The Air Force E/O guided bomb program, known as the Glide Bomb Unit (GBU)-8 (also known by its program nickname of HOBOS, which stands for Homing Bomb System), was designed to be what is called a 'modular' bomb. This means that the guidance kit (the seeker and guidance fin sections) would be literally bolted onto a standard -80-series bomb, which would act as the warhead. This meant that the warhead could be tailored for any kind of target that was required, be it heavy demolition (where a 2,000 lb./909.1 kg. Mk 84 would be appropriate), or area suppression (where a cluster bomb dispenser would be best). The GBU-8 was designed and built by Rockwell International in Columbus. Unfortunately, the USAF HOBOS had a poor combat career in Vietnam. There were a lot of single-point failures in various subsystems that made proper development of E/O bomb delivery tactics nearly impossible. But the worst of the problems revolved around the GBU-8 seeker itself. Because they had to actually see the target, the E/O bombs of the period could not be used in times of darkness or reduced visibility. In anything but 'perfect' conditions, the WSOs had to take manual control of the HOBOS through the data links and try to fly the bombs onto the targets. Frequently, they did not have time to make the necessary corrections before bomb impact.

By 1972, the shortcomings of the first-generation HOBOS were well understood, and the Air Force initiated a program to develop an improved family of E/O guided bombs. Now known officially as the Modular Glide Bomb System, the new program was designed to overcome the problems that had plagued the early HOBOS. Following a design competition under the Pave Strike program, the USAF selected Rockwell International as the winner to build what would now be called the GBU-15. The major improvements that the GBU-15 was designed to have over the earlier GBU-8 included:

• A longer standoff range to allow the launch aircraft to stay out of the range of SAMs and AAA guns.

• More maneuverability and cross-range performance, to provide greater tactical flexibility, and to improve endgame accuracy during approach to the target.

• An improved data link system, to allow greater control of the weapon during the terminal phase, the approach to the target.

• A greatly improved seeker system, with greater resolution and target discrimination capabilities.

• Options for improved seekers, including an infrared imaging (IIR) variant.

With these ideas in mind, the Rockwell International engineers got to work. Though they started fresh with the new design, Rockwell kept most of the good things that the GBU-8 had offered, starting with a standard Mk 84 2,000 lb./909.1 kg. bomb body as the warhead. This time, though, with the emerging miracle of integrated circuitry and microprocessors, Rockwell was able to do a much better job. Rockwell also added Hughes Missile Systems to the GBU-15 team; they produced the TV seeker from technology based on their highly successful AGM-65 Maverick air-to-ground missile. As an added bonus, a version of the seeker based on technology from the Imaging Infrared (IIR) version of the Maverick was designed and eventually fielded.

The basic GBU-15 is composed of a guidance/fin section, a bomb warhead, and a cruciform wing group (with steering fins) at the rear of the weapon. The following table shows the details of the various GBU-15 variants:

The initial E/O version was known as the GBU-15(V)-1. Originally operational in 1977 with the Israeli Air Force (the USAF spent five more years testing and developing it), it is currently cleared for use on the F-111F and the F-15E Strike Eagle. It was followed by the IIR version, designated GBU-15(V)- 2, and is favored by crews and planners. Some seventy of the GBU-15(V)-2s were expended in the Persian Gulf during Desert Storm in 1991. Like the earlier HOBOS, it is equipped with a two-way data link, with the instructions and seeker video data being fed through a pod, designated AN/AXQ-14. This allows the WSO of the launching aircraft, or another controlling aircraft, to actually fly the bomb onto a target with truly stunning precision. In addition, the data link system allows the seeker video to be recorded; this assists in bomb damage assessment (BDA), as well as providing CNN with exciting videos!

All the basic GBU-15s can be launched from a maximum range of 8 miles/14.6 km. at low altitude, and up to 20 miles/36.6 km. at higher altitudes. The key to this relatively long range is the lift capabilities of the cruciform wings at the front and rear of the GBU-15; these make the bomb an unpowered glider, with much greater maneuverability than previous HOBOS.

Following Desert Storm, several new variants, called the GBU-151 series, came into service with the Air Force. But at an FY-1991 cost of $227,000 per copy, a GBU-15 is anything but cheap, and further development is unlikely. There is, however, one GBU-151 variant which is rapidly gaining momentum, the Air-to-Ground Missile (AGM) -130. The AGM-130 is basically a GBU-151 with a small rocket motor strapped to its belly. This has the effect of extending the AGM-130's range to 16 nm./30 km. at low altitudes, and up to 40 nm./45.7 km. at higher release altitudes. It's an impressive set of capabilities for one family of weapons, though it places a great burden of responsibility on its operators. WSOs assigned to operate the GBU-15/AGM-130-series weapons have to be carefully trained, and have a delicate touch, to get the most out of this most accurate of PGMs.

Laser-Guided Bombs: The Paveway Series

Once there were two bridges that were the stuff of nightmares to U.S. pilots who flew over North Vietnam. The Paul Doumer Bridge over the Red River in Hanoi and the Dragon's Jaw Bridge (Ham Rung in Vietnamese) near Thanh Hoa were the toughest targets in a war full of tough targets. Prior to 1972, despite the efforts of thousands