They can always move

If you are a military person and you want to "get" some bad people literally holed up several hundred meters underground, what do you want? A nuclear "bunker busting" bomb. Naturally. What would you call it? Well the Bush Administration calls it a Robust Nuclear Earth Penetrator (since you know the Bush administration I feel confident I don't have to add the qualifying phrase, "No, really. I'm not kidding.").

But wait. The US arsenal already has one of those, you say, the B61-11 bomb. No good. Doesn't penetrate solid rock. For that we need nuclear (or if you speak dialect, nucular). This way you can get at the estimated 100 "potential-enemy" complexes built 100 to 400 meters underground or the 2000 strategic hardened or buried targets in urban areas. We know they are there because military intelligence sources tell us so. That's probably also where the Iraqi WMD are, too. If not, we'd like to put some of our own WMDs there.

The trouble is that to get good penetration you must detonate them a bit underground to get the required energy transfer downwards. And that turns out to be difficult, according to a National Research Council report issued April 27. This from an excellent article in New Scientist by Jeff Hecht:

Most of that advantage comes from penetrating just 3 metres into the ground. Once this depth is obtained, a 300-kiloton earth penetrator could destroy a target buried 200 m deep, while a 1-megaton weapon would be needed for a target 300 m underground.

The problem is that earth penetrators cannot plunge deeply enough into the ground to fully contain the effects of a nuclear blast, so casualties would be "for all practical purposes, equal to [those] from a surface burst of the same weapon yield”, the report suggests. That means surface casualties could be high.

[snip]

"Using an earth-penetrating weapon to destroy a target 250 meters deep - the typical depth for most underground facilities - potentially could kill a devastatingly large number of people," said John Ahearne, chair of the report committee.

Not to worry. Why are those people living near enemy facilities anyway? They probably work there. So if they don't want to be "taken out" along with the bunker, they should quit their jobs and move.

Update, 5/2/05: The Bulletin of the Atomic Scientists has more information in a piece by Jonas Siegel here (.pdf).