Robust Nuclear Earth Penetrator
According to a report on Australian Broadcasting: Pentagon wants bunker-buster funds back
The Bush administration has stated that no existing weapon in the Pentagon's arsenal is capable of destroying deeply buried targets such as underground bunkers containing chemical, biological and perhaps nuclear weapons or military command and control facilities.
Well, except for the BLU-113 Bunker Buster
that was used in Gulf War I. I realize it will only penetrate 20 feet of reinforced concrete or 100 feet of dirt, but every bunker needs an entrance to the surface. If you seal the entrance whatever is in the bunker is useless.
If you would really like an idea of what a bad idea this is: the funding was removed by a Republican controlled Congress.
Not convinced? Take six spikes out to your yard with a hammer. The rule is you can only hit each spike once. Drive in the first spike, then put the tip of the second spike on the head of the first spike and drive it. Continue until you run out of spikes. Carefully dig along the side of the spikes to see how straight the spikes are.
Multiple explosions to drive the warhead deeper with each explosion, a concept by someone who has never dug in a garden. There is almost no possibility that the weapon will continue on a designed path after it enters the dirt.