Government & Politics

Is new bunker buster too big for the job?

A B-2 Spirit stealth bomber.
A B-2 Spirit stealth bomber. file photo

The Star originally published this story on Oct. 23, 2009.

If your goal is to blow up things like, say, a budding but deeply buried Iranian nuclear program, a bigger bomb would be better, right?


The Air Force is spending $30 million on one of the heaviest bombs ever built, brawny enough to theoretically muscle its way into the side of a mountain or the stoutest of bunkers.

Even without nuclear innards – stuffed, instead, with conventional explosives equal to the weight of a small elephant in a casing as heavy as a small whale — the bomb could take out some of the world’s toughest targets.

The Pentagon expects to load the bomb next year on B-2 bombers based 50 miles from Kansas City.

In an age of bunkers — intelligence estimates put the number of hard and deep targets in the world at about 10,000 and growing — a weapon that can bust into a tunneled fortress becomes especially valuable.

“It’s possible that this is worth doing,” said Robert Pape, a professor of international politics at the University of Chicago and the author of Bombing to Win. “But it might be only a marginally more efficient way of blowing things up.”

If it works.

One test for the “massive ordnance penetrator” comes this week inside a tunnel at White Sands Missile Range in New Mexico. The test will see what damage the bomb can do underground.

The physics of bunker cracking is tough. Tests with a smaller bunker buster found that even when dropped from 40,000 feet, it penetrated just 20 feet into the soil.

Iran’s facility at Natanz, about 200 miles south of Tehran, may be buried as deep as 100 feet.

The Air Force, citing security reasons, only will say it expects the bunker buster to go deeper than existing bombs. John Pike, the chief defense analyst at, says it will go through about 200 feet of reinforced concrete. Some see that as unrealistic.

But does a bomb even need to go that deep? On the way to making a nuclear bomb, the Iranians would need to link thousands of high-speed centrifuges to separate the heavier and lighter isotopes in uranium gas — a delicate operation. Simply giving that facility a good jolt, without destroying it, the centrifuges could basically rip themselves apart.

Even nukes “have limited effectiveness at destroying the deepest or widely separated underground bunkers,” said a 2005 report from the Union of Concerned Scientists.

For starters, the bomb’s metal must be especially hard. The bomb needs to be slender, which leaves less room for explosives. The guidance system needs to be accurate — which is more difficult with the increased weight of an oversized bomb. The bomb also must hit the ground at the right angle. (In tests, some smaller bombs skipped like rocks on a pond.)

Adding more explosives helps, but at a rate of diminishing returns. A 30,000-pound device, for instance, blows up barely twice the packed earth as a 5,000-pounder.

“The upside of a bigger bomb is ... you might get by with one attack rather than two,” Pape said. “Then you don’t have to loiter over the target.”

Nuclear weapons have been contemplated for such targets, but scientists are skeptical about their ability to take out the deepest bunkers. Plus they would bring with them both radioactive and political fallout.

Yet the advantage of a supersized conventional bomb comes at some sacrifice.

While the new bomb could be carried by either a B-2 or a much older B-52, most strategists picture it in the smaller stealth bomber slipping by the defenses of a country like Iran or North Korea.

Program manager Sandra Davis of the Air Force Research Laboratory noted that the utter size of the bomb means “you need bigger machinery.”

Whiteman Air Force Base near Knob Noster, Mo., and the B-2 bases in the Pacific and Indian oceans would need new bomb-handling cranes.

Drawing from its existing arsenal, the B-2 can tote from 16 to 80 bombs, each one satellite-guided to separate targets. The B-2 soon will be able to carry more than 150 smaller bombs at a time.

But just two of the new monsters can squeeze aboard.

Reconfiguring the bomb bay for the big bunker buster would mean setting aside jets for that bomb. The Air Force has only 21 of the $2.1 billion stealth bombers in its fleet. At any one time, roughly one in three is either being repaired or upgraded. An undisclosed number are reserved for carrying nuclear bombs.

“You’re only going to have two or three, max, available to carry these weapons,” said Robert Hewson, the editor of Jane’s Air-Launched Weapons. “You may even find that it’s so restrictive on aircraft, a commander might choose not to use it.”

Pike sees it differently.

“It’s a powerful coincidence that (the Pentagon claims) it’s going to have this thing soon and we’re possibly going to be bombing Iran, “ he said. “There’s a mission made for this bomb.”

But other analysts wonder whether six 5,000-pounders bombing the same crater until the bunker is reached would serve as well. That would still leave 10 more bombs in a B-2’s quiver for other targets.

That could matter. If Iran’s nuclear facilities became targets, they would be many and varied.

“It’s the sort of thing that you’d quite possibly want to do in a single evening. It gets harder after that — operationally and politically,” Pike said. “And that means you’d want to hit as many things as possible.”

Even if it means with a smaller bang.

“If we can’t attack a target using 5,000-pound bombs, it’s probably nature’s way of telling us it’s pointless,” said Owen Cote, the associate director of security studies at the Massachusetts Institute of Technology.

Scott Canon: 816-234-4754, @ScottCanon