America's huge bunker-busting bomb is not sure to work in Iran
ISRAELI AIR strikes have destroyed some buildings on the surface of Iran's nuclear facilities, but the heart of the operation at sites such as the Fordow fuel-enrichment plant is still likely to be intact, hidden deep underground. Destroying this type of facility requires bunker-busting bombs more powerful than anything Israel can deliver. Donald Trump, America's president, has indicated in recent days that he is coming around to the idea of helping. On June 17th he warned 'our patience is wearing thin' with Iran. Reaching Iran's bunkers will take a special kind of bomb: the US Air Force's GBU-57 Massive Ordnance Penetrators (MOP).
The MOP is a huge weapon weighing 13 tonnes; conventional bombs are closer to one tonne. It is deployed on the UFO-like B-2 stealth bomber—flown exclusively by the US Air Force—which can carry only two at a time. The bomb has never been used in action.
The MOP is dropped from high altitude to smash through rock using sheer kinetic energy. It has a narrower profile than general-purpose bombs to concentrate the force in a small area, and most of its weight comes from its thick steel casing. Only 20% of the bomb's total weight is the explosive filler. The casing is a special ultra-strong alloy known as Eglin Steel (named after an Air Force base in Florida where it was developed). A MOP can reportedly penetrate 60 metres of standard concrete (see chart).
The bomb was first tested in 2007, and its design has been upgraded several times since. At least 20 are known to have been delivered in the first batch. As with smaller bunker-busters, MOPs are probably fitted with a void-sensing fuse which detects its surroundings and detonates when it emerges from solid rock into a cavity. A facility might have multiple levels, and the fuse can be programmed to explode on the third level underground, for example, in order to cause the most damage.
MOPs were developed by America's air force when it found that its existing bunker-busters could not damage Iraqi bunkers during the invasion in 2003. A new weapon had to be rushed into service. The MOP aimed to smash even deeper and harder bunkers being built in Iran and North Korea.
However, there are limits to what even the biggest conventional bomb can do. Whereas the MOP can go through over 60 metres of standard concrete, which can withstand 5,000 pounds-per-square-inch (psi) of pressure, that drops to eight metres for concrete of double the strength. In recent years Iran has advanced considerably in the field of Ultra High-Performance Concrete (UHPC), producing material with strengths of 30,000 psi or more.
And even if the bomb can break through, hitting the target may not be straightforward. MOPs need great accuracy to be effective and, like most American guided bombs, they rely on GPS satellite guidance. Military GPS is supposed to be jam-resistant, but in Ukraine American-supplied bombs have been severely affected by Russian jamming. In some cases it had reportedly decreased their accuracy from 20 metres to 1,200 metres before fixes helped to restore their accuracy. But jamming techniques have improved too, turning it into a cat-and-mouse game.
Israel is less reliant on GPS, and has alternatives such as the SPICE guidance system, which relies on cameras on bombs and uses AI-guided steering to reach the target. Israel has used weapons with SPICE in the current campaign against Iran. America may want to hastily retrofit this—or an American equivalent—to a MOP if America's generals lack confidence in GPS, although this process could take some weeks.
No conventional bomb except a MOP has a chance of finishing off Fordow, and only America can supply them. But even if Donald Trump decides to drop one (or even several), it is not assured to succeed.
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