"The US Air Force's BLU-113 "bunker buster" warhead was originally developed in a hurry during the 1991 Gulf War to attack fortified Iraqi command centres deep underground.
It is a 4,500 lb (2,041 kg) penetrating warhead, later used in Serbia and in Afghanistan, and now in the Iraqi capital, Baghdad.

It is carried in the form of the GBU-28 laser-guided bomb by the B-2 stealth bomber and F-15E fighter-bomber, or the GBU-37 satellite-guided bomb by the B-2 alone.

Satellite guidance means the bomb can be used even through cloud or smoke - because laser guidance, though highly accurate, is degraded by those.

The warhead includes more than 600 lb (272 kg) of high explosive - the rest is believed to be dense depleted uranium."

from the www