Brawny New Bunker Buster: 'Divine Thunderbolt'

By David Hambling
February 04, 2008 2:39:00 PM
Categories: Ammo and Munitions
Courtesy Of: Wired.com

The latest addition to the Air Force's arsenal of bunker busters is a 5,000lb weapon with formidable penetrating power. If you're going to attack the hardest of targets, you've got two options: go for the weak spot, like the Air Force's Portal Defeat program does; or simply to use the biggest, hardest bomb possible striking at high speed for maximum force. And that means the BLU-122. It replaces the BLU-113, a weapon with a rather colorful history. During the 1991 Gulf War it was discovered that shelters being used by some Republican Guard units were proof against existing bunker busters. The call went out to build something bigger and better -- and fast. In the absence of any suitable alternative, old eight-inch howitzer barrels were pressed into service and became the bomb's body. This crude but effective expedient resulted in a bomb which can go through twenty-two feet of concrete or a hundred feet of dirt. Details of the replacement have been scanty -- until now.

Designated the BLU-122, the new weapon is similar in size and shape to the BLU-113, but has been upgraded all 'round. Specifically, instead of being made out of an old gun barrel, the casing is now a custom-built ES-1 steel shell with much greater robustness. (Interestingly, ES-1 was specifically developed by the Air Force for just this sort of application). The fill has been enhanced: instead of 625 lbs of Tritonal mix, it contains 780 lbs of AFX-757, a thermobaric explosive which is both less sensitive and significantly more powerful. And the hardened nose has been modified to a shape known as 2.4 Triconic to give increased penetration through rock and concrete.

they included mounting the bomb on a rocket sled and running it into a stack of concrete blocks (pictured). The bomb's physical improvements seem to work well, with penetration inproved by some 20%-22% , which suggests that it can go through something like twenty-eight feet of concrete.

The explosives performed well: based on overpressure, the BLU-122 produced 70% greater blast than the earlier BLU-113.

However, the Achilles heel is the fuzing. As DANGER ROOM previously noted, the US has problems with hard target fuzes and looks like importing German technology for the job. But, as reported in the Divine Thunderbolt test report,

We Need A Hard target Fuze!....Portion Of BLU-122 Target Set Does Not Have A Capable Fuze

Until that particular problem can be resolved, the BLU-122 will not be quite as impressive at it looks.