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The US military's effort to build what may become the largest conventional bomb ever used is making progress.

Boeing announced on Monday that its Massive Ordnance Penetrator (MOP) demo weapon had successfully completed a "static tunnel lethality test" at the White Sands Missile Range in New Mexico.

It's being developed under the auspices of the US military's interestingly-named Threat Reduction Agency, which normally does things like verifying nuke disposals. The MOP is intended to reduce the threats faced by the USA only, of course, by pulverising them. From the viewpoint of other countries the new bomb could be described more as a threat enhancement.

Even so, to some the MOP seems like a relatively delicate tool. The US originally had a plan to deal with enemy bunkers, WMD facilities or whatnot using a special ground-penetrating nuke. The "Robust Nuclear Earth Penetrator" programme was axed by the Senate in 2005, however, leaving the MOP as America's last best hope for taking out difficult targets.

Bomb spotters may care to note that the MOP won't be the heaviest conventional bomb ever made by the US. The 1940s era T-12, at almost 44,000lb, was a substantially bigger brute. The T-12 was one of the final developments of the World War II Allies' "earthquake bomb" programmes, developed to knock out German V-weapon sites and U-boat pens. Famed British bomb boffin Barnes Wallis, inventor of the dam-busting "bouncing bomb", was an early innovator, designing the "Tallboy" and "Grand Slam" penetrators.

The T-12 didn't arrive in time for wartime use, and is now obsolete. The US does have some pretty hefty ordnance in current service, most famously the 21,700-lb GBU-43B Massive Ordnance Air Blast (MOAB) job – perhaps better known under its media nickname "Mother Of All Bombs".

The MOAB isn't any good for knocking out bunkers, however. It's a pure blast weapon, essentially a massive lump of explosive without penetrating abilities. It was developed to replace the old 15,000lb "Daisy Cutters" which US forces used to flatten jungle and create helicopter landing zones in Vietnam.

The MOP, however, should be just the ticket for deep bunkers. Most of its weight is actually in the hardened metal casing, which will strike the earth at several times the speed of sound after falling from high altitude. This should enable the MOP to drill a long way down before exploding.

There must be a lot of planners at the Pentagon scratching their heads right now over the Iranian nuke facility at Natanz, parts of which are said to be 75 feet underground and covered by metres of reinforced concrete. They'll be very keen to see the MOP ready for use. ®

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