A nuclear bunker buster, also known as an earth-penetrating weapon (EPW), is the nuclear equivalent of the conventional bunker buster. The non-nuclear component of the weapon is designed to penetrate soil, rock, or concrete to deliver a nuclear warhead to an underground target. These weapons would be used to destroy hardened, underground military bunkers or other below-ground facilities. An underground explosion releases a larger fraction of its energy into the ground, compared to a surface burst or air burst explosion at or above the surface, and so can destroy an underground target using a lower explosive yield. This in turn could lead to a reduced amount of radioactive fallout. However, it is unlikely that the explosion would be completely contained underground. As a result, significant amounts of rock and soil would be rendered radioactive and lofted as dust or vapor into the atmosphere, generating significant fallout.
Subsidence craters remaining after underground nuclear (test) explosions at the north end of the Yucca Flat, Nevada test site
B61 nuclear bomb
A bunker buster is a type of munition that is designed to penetrate hardened targets or targets buried deep underground, such as military bunkers.
A U-Boat pen after being hit by a Grand Slam. Note the figure standing on the pile of rubble.
An example of bunker busters at work at Ali Al Salem Air Base, Kuwait
GBU-57 Massive Ordnance Penetrator
A GBU-24 Paveway III strikes its target in a weapons test