The capability of the new B61-12 nuclear bomb seems to continue to expand, from a simple life-extension of an existing bomb, to the first U.S. guided nuclear gravity bomb, to a nuclear earth-penetrator with increased accuracy.
The National Nuclear Security Administration (NNSA) previously published pictures of the drop test from October 2015 that showed the B61-12 hitting inside the target circle but without showing the bomb penetrating underground.
But a Sandia National Laboratories video made available by the New York Times shows the B61-12 penetrating completely underground.
The evidence that the B61-12 can penetrate below the surface has significant implications for the types of targets that can be held at risk with the bomb. A nuclear weapon that detonates after penetrating the earth more efficiently transmits its explosive energy to the ground, thus is more effective at destroying deeply buried targets for a given nuclear yield. A detonation above ground, in contrast, results in a larger fraction of the explosive energy bouncing off the surface. Two findings of the 2005 National Academies’ study Effects of Earth-Penetrator and other Weapons are key:
“The yield required of a nuclear weapon to destroy a hard and deeply buried target is reduced by a factor of 15 to 25 by enhanced ground-shock coupling if the weapon is detonated a few meters below the surface.”