The US military plans to detonate a 700-ton (1.4 million pound) explosive charge in a test called "Divine Strake" that will send a mushroom cloud over Las Vegas, a senior defense official said. The explosive charge is equivalent to 75 GBU-43/B Massive Ordnance Air Blast Bombs (MOAB), the largest-ever satellite-guided, air-delivered weapon in history (blast photo at right).

"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 Defense Threat Reduction Agency.

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 told defense reporters.

"We also have -- are you ready for this -- a 700-ton explosively formed charge that we're going to be putting in a tunnel in Nevada," he said.

"And that represents to us the largest single explosive that we could imagine doing conventionally to solve that problem," he said.

The aim is to measure the effect of the blast on hard granite structures, he said.

"If you want to model these weapons, you want to know from a modeling point of view what is the ideal best condition you could ever set up in a conventional weapon -- what's the best you can do.

"And this gets at the best point you could get on a curve. So it allows us to predict how effective these kinds of weapons ... would be," he said.

He said the Russians have been notified of the test, which is scheduled for the first week of June at the Nevada test range.

"We're also making sure that Las Vegas understands," Tegnelia said.

The largest previous conventional explosive test was called Minor Scale, a test conducted by the United States Defense Nuclear Agency (now part of the Defense Threat Reduction Agency) involving the detonation of several thousand tons of conventional explosives for the purpose of simulating the explosion of a small nuclear bomb.

The test took place on June 27, 1985 at the White Sands Missile Range in New Mexico. Various sources indicated that between 2400 and 4800 tons of ANFO (ammonium nitrate and fuel oil) explosive were used to roughly simulate the effect of a four kiloton nuclear device. Minor Scale was reportedly "the largest planned conventional explosion in the history of the free world." Below is a photo taken in a split second after detonation. Note the F-4 Phantom II jet in the foreground to show the scale of the fireball.