We’ve talked a lot about Close Air Support here lately. Let’s talk a bit about a strike/interdiction for a bit.
Suppose you have a heavily defended, deeply buried underground command bunker that you absolutely have to take out, but don’t feel like losing a bunch of planes to do it. The bunker is buried too deep for a Tomahawk or ALCM cruise missile to destroy. What do you reach for?
The Air Force’s go-to weapon of choice for heavily defended hard targets is usually the AGM-130 missile.
While the splodey is nice, the interesting part of the story is the development history of this heavy hitter.
Most folks know the basic story of the development of the Precision Guided Munitions(PGMs) in Vietnam as regards Laser Guided Bombs (LGBs). Few folks, however, remember that at the same time as the LGBs were being developed and fielded that a second approach to precision attack was taken. Electro/Optical (E/O) seekers were developed that would allow the attacking aircraft to lock onto a target via the contrast between light and dark portions of a target. Theoretically, that contrast could be kept centered in the seeker field of view, and used as a steering command to guide a weapon to the target. As with the LGB approach, the Air Force decided to use a “modular” approach to weapons design. Instead of developing a bomb or missile from the ground up, the warhead would be an existing low drag bomb body, in this case, the 2000lb Mk84 bomb (designed, BTW, by that great American, Ed Heinemann). By simply adding the seeker and control components to an existing warhead, great cost savings could be achieved. The result of this “bolt on” development process was the GBU-8 HOBOS or Homing Bomb System. The HOBOS was used in Vietnam against several high value targets, but its performance was not entirely satisfactory. The biggest problem was that it often lost lock on targets that had only marginal contrast. Integration of the weapon with the fighters of the day, the difficulty of finding and locking onto a target while under severe anti-aircraft fire, and the limitation to daylight and fair weather use all contributed to making the HOBOS an “also-ran” compared to LGBs in Vietnam. LGBs were also cheaper weapons than HOBOS, since the expensive part of the guidance system, the laser, stayed with the attacking plane, and could be reused.
But that didn’t mean HOBOS was a dead end street. LGBs also had some limitations that E/O guidance didn’t suffer from. LGBs had to be guided all the way to the target, meaning that at least one jet had to stick around to lase the target. E/O bombs, though, were autonomous after launch, that is, they were “fire and forget” weapons. The attacking aircraft was free to maneuver and get out of Dodge as soon as the bomb left the rack. Further, LGBs were limited in range by the attenuation of the laser beam, and the lack of optical discrimination as the range to target increased. That is, if the attacking crew was too far out, the laser spot was too weak for the LGB to home in on, or alternatively, the crew couldn’t point the laser with sufficient accuracy to ensure a hit on a discrete target such as a bridge abutment. E/O guidance, however, actually improved as the weapon approached the target, as the decreased range improved optical resolution. If the seeker managed to maintain lock, the weapon generally hit exactly where it was aimed. And the potential for increased stand-off range for E/O weapons made them very attractive for continued development.
The Air Force continued to work on optical seekers, mainly for its AGM-65 Maverick family of missiles, and eventually fielded a family of seekers that could reliably maintain lock on. This was followed by seekers with image magnification, and finally, by using an Imaging Infrared (IIR) seeker that worked both during day and at night. About this time, someone had the bright idea to revive the HOBOS concept of an optical seeker using a Maverick seeker to improve reliability. Coupled with improved wings and control surfaces, the resulting weapon was the GBU-15 EGOB (Electro-Optically Guided Bomb), pronounced “Ee-gob.” The EGOB could actually be lofted to glide to the target from further out than its seeker could distinguish targets, so the next step was to incorporate a data-link that would transmit the seeker’s video imagery back to the launching aircraft. As the weapon approached the target, the launching aircraft could steer it onto the specific aim point, or even guide it all the way to impact.
One improvement leads to another. The AWX-13 digital datalink actually had a considerably greater range than the glide range of a GBU-15. So the next step in the improvement process was to bolt a powerful rocket motor to the bottom of the bomb. With this motor, the bomb, now called the AGM-130, could exploit the full range of the datalink, and keep the launching aircraft well away from enemy defenses. By bolting the guidance and control components to the BLU-109 2000lb penetrating warhead, the AGM-130 gave the Air Force the ability to hold at risk heavily defended hardened targets such as bunkers from ranges of up to 40 miles.
Even using the building block approach, the AGM-130 is a very expensive weapon. It wouldn’t typically be used for close air support where JDAMs or LGBs would be a cheaper, more viable alternative. Proper use of the AGM-130 requires extensive planning before launching the attack. The attacking aircrew has to know what the target will look like, both on its search radar, and through the seeker as it approaches the target. For a bunker in the middle of nowhere, that’s not a big challenge. But for a target in a built up area, that requires extensive planning and rehearsal. The primary carrier for the AGM-130 is the F-15E Strike Eagle. Typical targets might include air defense command nodes, airfields, bridges and critical logistical nodes.
What’s next for the AGM-130 family? It’s hard to say. Coupling its seeker with a GPS update or perhaps a millimeter radar seeker. But in any event, the evolutionary improvement using proven technology has yielded a battle tested weapon that can service targets while saving our aircrews from potential losses.