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Pentagon to use new bomb on Afghan caves

Department of Defense video shows a thermobaric bomb heading for a cave in testing.

WASHINGTON (CNN) -- The Pentagon is sending 10 new high-tech, bunker-busting bombs to Afghanistan that it says are more effective at destroying underground caves and tunnels.

The laser-guided bomb is a "thermobaric" weapon, a high-temperature, high-pressure explosive that uses a new class of fuel-rich explosive in its warhead. The explosive releases energy over a longer period of time than conventional explosives, allowing for a longer period of high pressure inside a confined space and creating more destruction via higher temperatures.

The Pentagon said Friday that tests show the thermobaric explosive is more effective in caves and tunnels. In an accelerated two-month field test completed December 14, the Air Force demonstrated that a ground-penetrating warhead filled with thermobaric explosives could destroy a mock tunnel target at a Nevada test site, the Pentagon said.

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U.S. troops and anti-Taliban Afghan fighters are searching hundreds of caves and tunnels in the mountainous Tora Bora region of eastern Afghanistan for any remaining al Qaeda or Taliban forces.

"It's something that we clearly have a need for in Afghanistan, and they're on their way over there," said Pete Aldridge, undersecretary of defense for acquisition.

Aldridge said the test in Nevada involved dropping a laser-guided bomb into a tunnel and exploding it with a delayed fuse. He said the bomb created "a significant growth in overpressure for the tunnel and temperature."

Known as the BLU-118B, the new warhead is fitted onto the BLU-109, a 2,000-pound air-launched bomb. Air Force F-15E fighter jets will launch the new weapon, which would find its target either by a laser or satellite guidance system.

Retired Air Force Maj. Gen. Don Shepperd, a CNN military analyst, said the new weapon is not a fuel-air explosive but works on a similar principle.

A fuel-air explosion results when a detonator ignites tiny particles of fuel. The explosion is similar to blasts that have occurred in industries, such as in a coal mine when coal dust in the air ignites and explodes.

Shepperd said the thermobaric bomb enters a cave and sends out a cloud of explosive particles. The bomb ignites the particles over a period of time, allowing them to spread further into a cave or tunnel, thus producing a larger explosion.

Dust and debris are shot out of the cave by the pressure created when the weapon explodes.

One key difference with the new weapon and previous bombs is that it doesn't completely destroy a cave, allowing U.S. troops to enter the cave after eliminating opposing forces.

"It can spread through these tunnel complexes and, in many cases, without actually destroying them," Shepperd said. "So it'll kill the people that are in there, but it won't collapse the cave. Then you can go in and find out what's in there, (that's) the idea behind these, if it works perfectly."

Shepperd said the additional time to build up pressure before the bomb explodes is short, measured in milliseconds. But it creates a more intense explosion with much more heat, he said.

"So this sucks air in and out of caves because of the thermobaric pressure that builds up there and the heat," Shepperd said. "So it's very effective against caves, and we rushed it together as we do in all conflicts."

Shepperd said the original bunker-buster bomb was put together hurriedly for the Persian Gulf War, adding that about six of them were used in that conflict.