[RightWhale]

"The earth-penetrating capability of the B61-11 is fairly limited...Tests show it penetrates only 20 feet or so into dry earth when dropped from an altitude of 40,000 feet.

That's if dropped into permafrost = ice. Doubtful there would be a command bunker under the permafrost.

[Amerigomag]

That's if dropped into permafrost

A quick trip down google indicates that current technology is not capable of delivering air dropped, low yield ordinance deep enough to insure containment by natural overburden.

Outside of the obvious problem of scale, the path of the ordinance provides a natural vent.

Sorry.