by Tom Clancy
But maybe even more amazing was the way Paveway bombs redefined the word hit. With LGBs frequently generating average circular error probability (CEP) miss distances under 10 feet/3.05 meters (a typical Vietnam-era F-4D CEP with "dumb" LDGP bombs was commonly 150 feet/45.7 meters), it frequently only took a single bomb from one plane to destroy a target which previously took a whole squadron of fighter bombers to hit. Quickly, the cry of "one bomb, one target" became a hallmark of LGB performance around Southeast Asia. As if to highlight the economy of the LGB effort further, a Paveway I guidance kit cost only about $2,700 in 1972 dollars — cheap compared to over $20,000 for a GBU-8 E/O guidance kit.
Paveway caused a revolution in aerial warfare, and it showed during the final U.S. air campaigns of the war, Linebacker I/II. During these efforts, which ran from May 1972 until January 1973, Paveway LGBs were the "magic bullets" of the American arsenal. They were everywhere, doing everything. In the south, LGBs from the 8th TFW (the only unit equipped with them at the time) helped stop the armored drive of the North Vietnamese at An Loc with an early demonstration of what would become known as "tank plinking" during the 1991 Persian Gulf War. In the north, they were dropping every vital bridge between the Chinese border and Vinh, as well as a variety of other vital targets.
Now, with all this success, there also came problems. While the LGB seeker would guide the bomb to an almost perfect bull's-eye every time, the bomb had to be dropped within a fairly narrow "basket" in the sky (within a few thousand feet of a "perfect" ballistic launch point) for the bomb to have the necessary energy or "smash" to reach the target. This meant that in Vietnam, the Paveway I-series bombs had to be dropped from medium to high altitude (above 10,000 feet/3,048 meters); low-level drops (less than 10,000 feet/3,048 meters) were completely out of the question. In addition, clear visibility in daylight was a must, because the early Paveway I designators did not have low-light or thermal imaging systems. In fact, until the introduction of the AAQ-26 Pave Tack targeting and designation pod in the late 1970s, the designators were the major limitation in the use of LGBs.
The first designation system that made LGB drops in high-threat areas viable was the Pave Knife built by Ford Aeronutronic (now Loral Aeronutronic). Hand-built and fielded by a team led by the legendary optical engineer Reno Perotti, the six prototype Pave Knife pods that were available became one of the single most important factors to the continued success of the Linebacker campaigns in 1972.
In the late 1970s, DoD began fielding a new version of the bomb-guidance kit, the Paveway II. Essentially a production version of the hand-built Paveway I-series kits, they provided the USAF, USN, and USMC with their primary PGM capability well into the 1980s. They have even enjoyed a measure of export success, including use by the British in Desert Storm. In fact, Paveway II-series kits are still in the U.S. and NATO inventory, and will continue to soldier on well into the 21st century.
The Paveway II kits come in three varieties, broken down by the following bomb configurations:
The Paveway II-series bombs proved to be extremely successful, and have enjoyed a long and useful career. The first attempted combat use of Paveway II appears to have occurred in October 1983, when an A-6E from the USS John F. Kennedy (CV-67) dropped several LGBs on targets in the Beirut area. Unfortunately, problems with the ground-based laser designator caused them to miss their assigned targets. They saw their first really successful combat trials during Operation Prairie Fire in 1986, a series of confrontations between the U.S. Navy and Libya in the Gulf of Sidra. During the famous "Line of Death" confrontations, USN A-6Es used Paveway II-series bombs to help destroy/disable several Libyan patrol boats. Later, they were used during Operation Eldorado Canyon, the joint April 1986 USAF/USN/ USMC raid on Benghazi and Tripoli.
One of the Paveway II configurations, the diminutive 500 lb./227.3 kg. GBU-12, proved to be one of the most important weapons of the 1991 Persian Gulf War. In late January and early February of 1991, CENTAF BDA teams showed that the "battlefield preparation" in the KTO (Kuwaiti Theater of Operations) was not destroying enough armored vehicles and artillery pieces with standard LDGP bombs to meet the proposed attrition target of 50 % prior to the start of the ground war.
To help overcome this problem, Major General Buster Glosson, the CENTAF Director of Operations, came up with an idea called "tank plinking." General Charles A. Horner, the commander of CENTAF during the war, is said to have been told by the commander of CENTCOM, General H. Norman Schwarzkopf, to never call this tactic "tank plinking." General Horner, always the obedient fighter pilot, promptly ordered his staff to make sure that everyone always called it "tank plinking."
Here is how tank plinking worked. A flight of F-111Fs or F-15Es would fly over an Iraqi artillery or armored unit shortly after sunset. Since the sand of the desert cooled faster than the military equipment dug in among the dunes, the vehicles and artillery tended to show up as "hot spots" in the aircraft's FLIR targeting systems. They would then drop one of the "old" GBU- 12s on the desired target, and the results were, in a word, spectacular. Despite what you might think, even a main battle tank cannot have armor everywhere, especially on top. Thus, when one of the "little" LGBs hit one, the target would go up in flames, and the BDA assessments were quite positive. The fact that an F-111F might carry four GBU-12s, and an F-15E up to eight, meant that tank plinking was a surprisingly economical way of killing targets up in the KTO. Every night, for several weeks in early February 1991, the 4th and 48th TFWs would send pairs of F-15Es and four ship flights of F-111Fs into the KTO to hunt artillery and armor targets. The results were spectacular. Often, the small formations would come home with anything from twelve and sixteen targets killed per mission.
Combined with the capabilities of an integrated thermal imaging/laser designation/weapons delivery system, the Paveway II-series LGB was a formidable weapon when properly employed. Formidable, but very limited. Paveway II still had a very small launch "basket," which diminished its utility in high-threat environments. In particular, its low-level capabilities were highly restrictive, making its utility in that mode marginal. Even with drops from 20,000 feet/6,096 meters, the favored altitude for Paveway II drops, there were challenges for the crews.
Even before Paveway II went into combat, the Air Force and TI had begun to develop the replacement for the Paveway II under a program called the Low-Level Laser-Guided Bomb (LLLGB). Begun in 1981, it was designed to overcome the shortcomings inherent in the previous Paveway II bombs and take full advantage of the new series of laser designator systems being deployed worldwide. The result was the Paveway III series of bombs, which came into service in the mid-1980s.
The key was to be an all-new guidance section, which would be equipped with a microprocessor-controlled digital autopilot adaptive to the flight and release conditions. There are a variety of settings for delivery aircraft, flight mode, warhead configuration, laser coding, and delivery profile. Even more important, with a change of the Programmable Read Only Memory (PROM) chips which hold the autopilot software, the basic guidance package can be adapted to a variety of bomb configurations and capabilities. The changes to Paveway III start at the front of the seeker with the seeker dome, which is made of Lexan plastic with a fine wire mesh. Inside this dome is an optics housing containing a four-quadrant laser sensor and optics to focus the spot of laser light from the laser designator. The simple four-quadrant detector in the seeker is the touchstone of the Paveway program's simplicity, and is one of the keys of its success. And the sensitivity of the seeker itself has also been improved, so that even low-power laser designators (or standard designators degraded by weather) can be used. The seeker housing is gimbaled in two axes, and can scan in a bar (horizontally, back and forth), box (rectangular), or conical (circular) mode. Aft of the seeker is the guidance electronics section, which contains the autopilot, laser decoding, and signal processing circuitry, as well as the rotary switches for programming the bomb. The control setting switches are mounted flush with t
he exterior of the airframe, and can be set with almost any flathead tool, though the "ordies" (ordnance technicians) from the 391st Fighter Squadron at Mountain Home AFB (they fly the F-15E Strike Eagle) tell me that a quarter works best for this job.
The laser seeker, guidance electronics, and control section form what is termed the Guidance and Control Unit (GCU), which is attached to the front of the selected warhead. Paveway LGBs have always made use of standard USAF munitions as the warhead; and Paveway III is no exception. It can be attached to any of the 80-series bombs, as well as the BLU-109/B penetrating warhead. At the rear of the warhead is mounted the cruciform airfoil group. This is a tail section equipped with four pop-out wings to help stabilize the weapon during its flight. Along with mounting lugs for the bomb rack on top of the weapon, this is the makeup of a complete Paveway III LGB.
The first production versions of the Paveway III were the GBU-24 family, which entered service in the mid-1980s. Designed as the general purpose LGB, the GBU-24 quickly became the primary weapon of the F-111Fs of the 48th TFW at RAF Lakenheath. It is the airfoil group, with its large spring-deployed planar wings, that makes all the difference in expanding the launch and delivery envelope of the GBU-24. When the wings are fully extended some two seconds after the bomb is dropped, they have twice the lift area of the Paveway II-series airfoil group, and give the GBU-24 a glide ratio of 5:1, meaning that for every foot/meter of altitude lost in flight, the bomb can travel forward five feet/meters. This means that the launch envelope for the GBU-24 is vastly greater than the Paveway II-series bombs, and gives it the energy and maneuverability for a lot of tricks.
The second version of the GBU-24 family, while a bit different, became one of the stars of Desert Storm. This variant has a BLU-109/B penetrating bomb warhead, designed to punch through heavy reinforced concrete and armor. Called a GBU-24/B, it was Saddam Hussein's greatest nightmare, and his worst tactical surprise when Desert Storm kicked off. With the exception of a handful of command bunkers outside of Baghdad, it was capable of destroying every hardened target in Iraq. This included the Yugoslav-built hardened aircraft shelters (HASs) that had been previously thought to be impervious, even to a near-miss by a tactical nuclear device! The GBU-24/B is composed of the same components as the basic GBU-24/B, with the difference of the BLU-109 being substituted for the Mk 84. In addition, there is a spacer attached to the bomb body called an ADG-769/B Hardback. This helps maintain the same tail clearances as the larger-diameter Mk 84. In addition, there is only one fuze, an FMU-143/B delayed action unit mounted in the rear of the BLU-109/B. Other than that, the two models are identical, with the necessary software to operate both models already being built into the common guidance and control unit. A third variant, the GBU-24B/B, is an improved GBU-24A/B.
The fourth variant of the Paveway III family is a unique version for the F-117A Nighthawk Stealth Fighter, the GBU-27/B. The reason for this is that the F-117A design was frozen before the new bomb was even in design, and the Lockheed designers had originally assumed that they would only have the older Paveway II-series weapons with their relatively small airfoil groups to fit into the weapons bays of the F-117s. With the coming of the Paveway III- series weapons, though, the USAF wanted to get the new bombs, especially ones equipped with the BLU-109/B, onto the new stealth birds. The problem was that the BSU-84/B airfoil group was too large to fit into the Nighthawk's weapons bays. This problem was overcome when the TI and Lockheed designers realized that the F-117A was almost never going to fly the kind of low-level delivery profiles that the F-111Fs and F-15Es were going to. In fact, the Nighthawk normally flies its weapons delivery profiles straight and level at various altitudes, dropping its precision weapons under the control of the pilot. Thus, the TI designers came up with a slightly different version of the fin group used on the Paveway II family, which fits nicely inside the limited volume of the F-117A weapons bay. The normal warhead of the GBU-27/B is the BLU-109/B, though the Hardback adapter is deleted because of the unique "trapeze" weapons handling gear of the Nighthawk.
A drawing of the GBU-24/B Paveway III Laser-Guided Bomb.
Jack Ryan Enterprises, Ltd., by Laura Alpher
The final version of the Paveway III family deserves special attention. It is the famous "Deep Throat" super penetrator bomb that was used on the last night of Desert Storm. Officially designated as the GBU-28/B. Its origins date back to August 1990, when the first planning for an offensive air campaign against Iraq began. As the planners in what was known as the Black Hole began to look at strategic targets around Baghdad, they noted a series of super-hard command and control (C) bunkers, so heavily built that there were doubts about the ability of the BLU-109/B warhead to penetrate and destroy them. With this in mind, a request was made to study the problem at the USAF Air Armament Division at Eglin AFB, Florida. Down at Eglin AFB, a quiet study was started to look over the problems associated with an improved penetrating bomb. In the study group, headed by Major Richard Wright, there was an engineer named Al Weimorts, who began to make some early sketches of a concept bomb that might just do the job. And that was where the idea stayed until the early BDA results from Desert Storm began to come in. By January 21st, 1991, it was clear that the BLU-109/ B-equipped LGBs were just not getting the job done. All they had done to the big bunkers was scab the surface, and not much else. Worse, with more and more of the other Iraqi C bunkers being destroyed, a greater percentage of the top Iraqi leadership was taking refuge in the big command bunkers and continuing operations. This made the destruction of those bunkers a top priority, and the word went out to the team down at Eglin to find a way to do so quickly.
Given their marching orders, TI, as well as the BLU-109/B team at Lockheed, got to work on a number of different problems at once. First there was the problem of the warhead. While the basic design of the BLU-109/B was sound, what was needed was something larger — longer and heavier, with a larger explosive payload. Also, because they had to bolt a modified Paveway III kit onto it, and because they had to maintain the necessary clearance to fly and drop it from either an F-111F or F-15E, it would not have a larger diameter than the BLU-109/B. This made for a long, skinny warhead section, with a long interior cavity, or "throat," for the explosive filler. Thus the bomb got the nickname "Deep Throat."
The two GBU-28/B "Deep Throat" super penetrating bombs at the Royal Saudi Air Force Base at Taif just before being loaded onto F-111F fighter bombers of the 48th Tactical Fighter Wing (Provisional). The BLU-113/B warheads have already had their fin groups mounted, and the guidance sections will be mounted once loaded.
Captain Ron Evans
Next, to machine and finish a forged-steel blank would take months, and the Eglin team had days. Luckily, an engineer at the Lockheed plant where the BLU-109/Bs were made was a retired U.S. Army trooper who remembered a stock of old 8-inch/203mm howitzer gun barrels lying around (literally) at the Letterkenny Arsenal in Pennsylvania. Made of the same kind of hardened steel as the BLU-109/B, they had been happily rusting away for some time. By February 1st, 1991, a number of the old gun barrels were shipped to the Watervliet Army Arsenal in upstate New York and machined into the shape of what would become known as the BLU-113/B Super Penetrator. Eventually, around thirty-two of the BLU-113/Bs would be built for integration into what was going to be known as the GBU-28/B. Several inert (non-explosive) tests indicated that the new bomb was capable of doing the job. This included one test on a rocket sled at Holloman AFB, New Mexico, where it penetrated 22 feet/6.7 meters of reinforced structural concrete, and then continued on to careen downrange for another mile or so without any damage whatsoever to the BLU-113/B. Each of the new warheads eventually weighed in at 4,700 lb./2,136.4 kg., and had to be hand-loaded with some 1,200 lb./545.45 kg. of explosive, and then integrated with the guidance kits from TI.
Those guidance kits were a whole story on their own. Meanwhile, the original Paveway III development team had long since moved onto other jobs within TI, and had to be reconstituted as
quickly as possible. Murl Culp from Lockheed contacted TI and discussed the feasibility of guiding the new penetrator with a derivative Paveway III GCU. Luckily, Bob Peterson, an original Paveway III engineer, was still with the company, and was able to reassemble enough of the original team to get the ball rolling. And other members of the team were pulled off of other important TI programs to staff the effort. By February 12th, the TI/Lockheed team was down at Eglin AFB briefing guidance concepts to the Air Force.
Once the new guidance software was completed, the major testing normally associated with development of a new Paveway GCU would have to be accomplished in days rather than years. A key problem was access to the only wind tunnel in the Dallas/Fort Worth area capable of doing the testing required to develop and validate the new LGB's software. Owned then by LTV/Vought, it was heavily booked with projects, and the security around the GBU-28/B precluded doing anything special to "force" the owners to provide access for TI. Thus, TI would have to use the only open "window" on the tunnel's calendar, on the weekend of February 16/17, just four days away. Now, it should be remembered that at the time all of this was going on, TI, Lockheed, and the Air Force did not have any sort of contract for this project. What they did was done on a handshake and good faith, and TI decided to trust in that when they scheduled the tunnel time. They constructed a 1/4 subscale model to establish the ballistics of the new BLU-113/B/Paveway III combination, which was designated the GBU-28/B.