The Massive Ordnance Penetrator (MOP), AKA the GBU-57, commonly referred to as a bunker buster, was developed after U.S. intelligence discovered in 2009 that Iran was tunneling deep under a mountain near the city of Qom for the express purpose of creating weapons-grade uranium. As much as half a mile below the ground, such a facility would be beyond the reach of any bunker buster in the U.S. arsenal. The best bunker buster the U.S. military had, the GBU-28, was only capable of penetrating 20 feet into hardened concrete. That may have been good enough for Saddam Hussein’s bunkers during the U.S.-Iraq War, but not enough to even rattle the plates—or upset the uranium-enriching centrifuges — at Fordow.
What followed was a 15-year program to develop the next generation of bunker busters capable of penetrating 60 to 200 ft[i] below ground. Even if that may have not been deep enough to penetrate into the space where the centrifuges spun, might the bombs collapse the ceilings or the centrifuges be ruined by shockwaves?
The Centrifuges at Fordow
The Fordow Fuel Enrichment Plant is (was?) Iran’s deeply buried uranium enrichment facility, near Qom. It was said to house three to four thousand centrifuges. Fordow’s initial centrifuges go by the IR-1 designation, Iran’s derivative of Pakistan’s P-1. They were joined by the more advance IR-6 in 2019, reported Reuters.
Fordow’s centrifuges are housed in underground halls in approximately 70,000 square feet of total space.
Each centrifuge features a tall aluminum or carbon-fiber rotor that spins at 1,000–1,500 revolutions per second.
These machines are highly delicate—small vibrations or even modest overpressure can cause damage. They are dynamically balanced and rely on perfect alignment. They are highly susceptible to vibration, ground shock and blast waves.
Even if the facility isn’t penetrated or collapsed, the pressure wave and shock can misalign bearings, warp rotors and fracture casings of the centrifuges. The strikes could also impact support systems, including electrical and cooling systems. A blast or impact could also cause structural instability and, if close enough to the interior, cause spalling[ii].
IAEA inspectors have noted in other enrichment sites that relatively minor seismic tremors can cause significant damage to centrifuges.
Weoponeering
In 2009, the U.S. military “weaponeers[iii]” set about developing a 30,000 lb bomb capable of damaging, if not penetrating, deep underground targets like Fordow. They could count on gravity for a high terminal velocity (secret, but rumored to be near Mach 1 or greater) and previously developed technology for guidance and control to hit the precise location, but to achieve penetration depth as much as 10 times the previous bunker buster involved considerable analysis.
“In the beginning of its development, we had so many PhDs working on the MOP program, doing modeling and simulation, that we were quietly and in a secret way, the biggest users of supercomputer-hours within the United States of America,” said Chairman Gen. Dan “Razin” Caine in U.S. Department of Defense briefing after the U.S. strike against Fordow.
In the development of the GBU-57, the Defense Threat Reduction Agency worked with Pentagon teams to model geology, concrete reinforcement, subsurface layout, and ventilation shafts at Fordow. Analysts created detailed digital replicas of the target site to simulate bomb penetration, fuse behavior, impact angle, etc.
The Pentagon conducted repeated full-scale test drops of the MOP (hundreds, according to Caine’s account), utilizing computer models and supercomputer simulations to verify performance against realistic underground structures.
To achieve maximum damage, precise modeling for penetration depth and destructive yield was essential. Each bomb’s impact had to be subtly tuned—arrival angle, velocity, and delay settings were computer-optimized. Supercomputing enabled analysts to iterate on weapon designs rapidly, minimizing field testing and ensuring peak effectiveness before deployment.
Of course, the military would not use commercially available cloud servers, such as those provided by Amazon (AWS), Google and Microsoft (Azure). While a number of FEA programs can simulate underground explosions, including Dassault Systèmes ABAQUS, Ansys Autodyn, LS-DYNA and FLAC3D, no simulation company could be expected to develop multiphysics simulation for high-speed impact and explosion for a market of one — even if that one was the U.S. military.
No matter. The U.S. has resources aplenty. Not only did the U.S. national labs have plenty of their supercomputers but they also had the software. It would not be the first time they have been called into service to build a new weapon. Gen. Caine did not give any one lab credit but we can expect Sandia National Laboratories to have answered the call. They had developed their own CTH code to analyze the effects of shock. And Lawrence Livermore National Laboratory, too, for they had developed SIERRA, a platform for engineering mechanics.
Did It Work?
Fordow sits under what might be as much as half a mile of rock. The MOPs, even two strikes on the same spot, as was said to occur at Fordow, could not drill that deep. They may not have needed to. The highly sensitive machines could have been knocked out of commission from the shock waves.
In an interview with French media, Rafael Grossi, director general of the International Atomic Energy Agency (IAEA), told Radio France Internationale (RFI), “Obviously, we can’t assess the degree of damage. But given the power of these devices and the technical characteristics of a centrifuge, we already know that these centrifuges are no longer operational, because they are fairly precise machines. There are rotors, the vibrations have completely destroyed them.”
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[i] The original spec for the GBU-57 gave the penetration depth as 60 ft, but current accounts state penetration depth of 60 m, approximately 200 ft.
[ii] A penetrator, like an anti-tank round, can damage by spalling, caused by shock waves travelling from the impact surface to the interior surface, loosening material that retains a significant portion of the kinetic energy from impact.
[iii] Weaponeering is a portmanteau of “weapon” and “engineering.” You can’t get a degree in weaponeering, it is learnt on the job. It is the process of determining the quantity of a specific weapon needed to achieve a target effect. The term may have first been used during the Vietnam War, as discussed in this paper in the Military Review.