From 24/7 News.com Australia

The United States military planned to detonate a 700 tonne explosive charge in a test called “Divine Strake” that would send a mushroom cloud over Las Vegas, a senior defence official said.

“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,” said James Tegnelia, head of the Defence Threat Reduction Agency.
Mr Tegnelia said the test was part of a US effort to develop weapons capable of destroying deeply buried bunkers housing nuclear, chemical or biological weapons.

“We have several very large penetrators we’re developing,” he said.

“We also have - are you ready for this - a 700 tonne 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.”

Read More Vegas