Bunker busting: "Divine Strake"

From The Guardian's Julian Borger: "Pentagon plans record-breaking explosion in Nevada desert"

The Pentagon is preparing to set off a record-breaking bang, detonating 635 tonnes of high explosives and sending a mushroom cloud into the sky over the Nevada desert. The blast, on June 2, codenamed Divine Strake, is likely to be the biggest controlled conventional explosion in military history, experts said, and is designed to test the impact of bunker-busting bombs aimed at underground targets.
The blast comes at a time of rising tension with Iran over its nuclear programme. The US has refused to rule out military action and is considering the feasibility of destroying underground warhead development sites Iran is alleged to have built.
"We have several very large penetrators we're developing," James Tegnelia, head of the Defence Threat Reduction Agency (DTRA) told US defence reporters. "We also have - are you ready for this? - an explosively formed charge that we're going to be putting in a tunnel in Nevada ... and that represents to us the largest single explosive that we could imagine doing conventionally to solve that problem."

Aha. The WH doesn't want Iran to get dabomb so it 'asked' Congress to approve nuclear bunker-busting bombs to penetrate Iranian underground facilities. Too many ironies... must... not... let head explode!

Alas, poor Yorick did not get his new baby-nukes (just yet). These are ol' fashioned--just friggin huge mofo bombs:

The explosive used will be ammonium nitrate soaked in fuel oil - a cheap but potent combination. "I don't want to sound glib here but it is the first time in Nevada that you'll see a mushroom cloud over Las Vegas since we stopped testing nuclear weapons," Mr Tegnelia said.
Ivan Oelrich, a munitions expert at the Federation of American Scientists, said: "I suspect this is primarily a test of their computer modelling abilities, because I don't know how they could deliver a weapon like this. They are looking at how different rocks respond to shockwaves."
The White House and the Pentagon wanted to develop a nuclear bunker-buster bomb, but the initiative was blocked by Congress, obliging the defence department to experiment further with conventional explosives.

FYI, the US has used so-called "bunker busters" (thermobaric) bombs in Afghanistan and has been waiting with blueballs to develop the nuclear variety since forever. Well, at least since March 2005's "Joint Publication 3-12: Doctrine for Joint Nuclear Operations." Check out this gem (pg. III-I, under "Preparation"; emphasis mine):

Responsible security planning requires preparation for threats that are possible, though perhaps unlikely today. The lessons of military history remain clear: unpredictable, irrational conflicts occur. Military forces must prepare to counter weapons and capabilities that exist or will exist in the near term even if no immediate likely scenarios for war are at hand. To maximize deterrence of WMD use, it is essential US forces prepare to use nuclear weapons effectively and that US forces are determined to employ nuclear weapons if necessary to prevent or retaliate against WMD use.