Did America’s Biggest Bomb Just Bounce Off a Mountain?

The GBU-57 is supposed to be the hammer of God. But Iran’s Fordo site may have just shrugged it off.

I was on vacation when it happened, naturally. Every time I take a little time off (this time my first visit to NYC), something happens in the world that I would normally write about; you know, being a miltech writer and all…

So, I’m sitting down eating at a Mexican food restaurant in Times Square called the “Pink Taco” (not kidding), and I receive a notification on my phone from CNN. “Trump bombs Iran.”

Afterward, Trump claimed that the Iranian nuclear site at Fordo was completely “OBLITERATED.”

Well, that’s reassuring. But… How does he know, for sure?

That’s when someone at the Defense Intelligence Agency (DIA) leaked an assessment that cast doubt on Trump’s claims.

American B-2 Spirit stealth bombers dropped what should have been the final word in conventional airpower: fourteen GBU-57A/B Massive Ordnance Penetrators. Thirty thousand pounds of solid hate designed to bore through nearly 200 feet of rock and obliterate whatever lies beneath. In this case, that would be Iran’s deeply buried Fordo uranium enrichment facility, dug into the base of a mountain like a doomsday prepper with a fossil fuel budget.

The strike was supposed to be decisive. Final. Infographics made it look like a straight shot into the Earth’s crust, followed by a biblical underground fireball.

But here’s the problem: it may not have worked; at least, not as well as the Pentagon might believe.

Let’s Talk About That DIA Assessment

A classified assessment from the Defense Intelligence Agency suggests that the bombs caused “limited damage.” Not zero. But not the “glass crater” some Pentagon PowerPoint warriors had in mind either. According to one US official who spoke to NPR on the condition of anonymity, Fordo’s advanced centrifuges might have been set back a few months, maybe.

Satellite imagery shows some new scars on the surface, possibly entry holes from the penetrators. But the underground complex? Still standing. Still spinning.

The White House denies it, calling leaks of the DIA report an attempt to embarrass President Trump. “Everyone knows what happens when you drop fourteen 30,000-pound bombs perfectly on their targets,” said Press Secretary Karoline Leavitt. “Total obliteration.” Except… no. Not necessarily. And not if physics has anything to say about it.

We’ve known this for decades: penetrating rock is hard. Really hard. After 9/11, good ole George W. Bush considered using low-yield nuclear bunker busters to collapse al-Qaeda’s mountain hideouts. But scientists ran the numbers and concluded there was no way to get a nuclear warhead deep enough to avoid spraying radioactive debris everywhere.

Thankfully, that hare-brained project got canceled.

The GBU-57 is what we ended up with instead. Well, that, and the MOAB, for Massive Ordinance Air Blast; technically called the GBU-43/B. Also called the “Mother of All Bombs.”

Are these bombs impressive? Absolutely.

But still bound by Newtonian laws and geologic reality. Weapons are built in labs. Targets under mountains are built by tectonics. That’s the mismatch.

Bunker busters like the GBU-57 were engineered with equations, simulations, and high-speed footage of steel slamming into sand. But Fordo? Fordo was built by geology, not geometry. And rock doesn’t read engineering specs.

Let’s start with the basics. The physics of penetration is governed by a few core variables: weapon weight, impact velocity, nose shape, and the medium it's trying to tunnel through. These aren’t negotiable. You don’t get to wish your bomb deeper just because your target is inconveniently deep.

That’s where an interesting US government contractor report written by C.W. Young comes in. The title of this riveting 37-page read is simply “Penetration Equations.”

Young’s equations, the ones engineers plug into when they want to know how deep something will actually go, are not a secret. It’s been around for decades. And it doesn’t care about how many YouTube explainer videos your bomb has.

Surprise, surprise! It turns out that the Earth’s composition at your bombing site determines the penetration depth.

Drop a GBU-57 into forgiving soil and you might get 80 meters.

Into fractured limestone? Closer to 20.

Into Fordo’s suspected bedrock? Maybe 7 or 8 meters.

That's it. After that, the bomb has bled off its kinetic energy and starts acting more like a very expensive doorstop.

And here's where it gets even more unforgiving: the deceleration forces. As that 30,000-pound weapon slams into the earth, it endures g-forces that would turn a human body into a fine mist. Its internals have to survive that punishment while staying operational. A failure in the nose cone’s structural integrity or internal wiring is a $3 million faceplant.

None of this is new. These problems have been staring back at engineers since the earliest earth-penetrator weapons. During the 1980s and 90s, scientists ran live tests into hard soil, reinforced concrete, and various rock substrates. The pattern was always the same: bombs can’t cheat geology. Medium-strength rock slows them like molasses in winter.

Hell, there’s even a 4,500 lb bunker-busting “Disney bomb” used during World War II and named after Walt Disney because he provided the inspiration for its design.

The Disney bomb, ladies and gentlemen! I must have missed this exhibit at Epcot.

(I presume this particular bomb sang “It’s a small world, after all” as it penetrated Nazi submarine pens.)

And even when you get the math right on paper, the real world still adds wrinkles. Moisture content in the soil. Seasonal temperature shifts. Subsurface voids or pockets of denser material. These aren’t footnotes; they're wildcards that can tank the best-case scenario.

So, when someone says, “Why didn’t the bomb reach 60 meters like the diagrams showed?” the answer is simple: the diagrams were Boeing marketing. The rock was real.

It’s Not Just Depth… It’s Direction

Rocks aren’t homogeneous. They fracture, shift, and mess with the bomb’s path as it slams through. Even minor variations in geology, say, a fault line or a dense seam, can knock the weapon off course. And if the casing warps or deflects mid-burrow, even a millimeter shift on impact can translate to meters of miss inside the target zone.

Raymond Jeanloz, one of the original authors of that 2005 study, put it plainly: “If there's any variation, including fractures or gaps, that can deflect the trajectory into the ground.” Translation: the Earth fights back.

So why drop fourteen?

Ah, USAF thinking 101. Because when you’re not sure if one hammer will crack the safe, you bring a whole toolbox and start swinging.

Fourteen GBU-57s were insurance. When you're staring down a target like Fordo, buried beneath a mountain and likely hardened with reinforced concrete, rebar cages, and years of Iranian engineering paranoia, the math alone doesn’t give you confidence. So, you throw redundancy at the problem.

But there was method in the saturation. It wasn’t a blind carpet-bombing. Satellite imagery and acoustic data suggest that many of the bombs were dropped in tightly grouped pairs.

That’s a classic tandem strategy. The first bomb acts like a battering ram; its job isn’t to destroy the facility, but to loosen the surrounding geology. It fractures rock, creates micro-fissures, and softens up the substructure.

Then, moments later, a second bomb slams into the same hole, aiming to ride that fractured channel deeper. If everything goes perfectly, and it rarely does, you get a multiplying effect on penetration.

There’s also targeting logic. Fordo’s entrance and ventilation shafts, electrical substations, and possible elevator shafts would all be high-value choke points. You don’t need to vaporize the entire facility to cripple operations. You just need to collapse the exits, blind the sensors, or disrupt cooling systems.

If just one bomb seals a main shaft or melts server racks, that could buy you months.

And then there’s the unknown unknowns. Maybe planners weren’t confident about the geology beneath every aim point. Maybe the GPS data had a margin of error. Maybe the facility had decoys or dummy bunkers.

The answer to all of that? Drop more. Cover more ground. Create overlapping shockwaves. Make the site a seismic migraine.

DoD released

But more bombs also bring more chances for deviation. Each weapon’s trajectory might get skewed by buried faults or dense inclusions. By dropping fourteen, you’re rolling the dice enough times that one might get lucky.

Or maybe the bet was never on precision, but on pressure. A message sent in deep decibels: we know where you are, and we can reach you, even if just barely.

By the way, if my math is correct, and it rarely is, the US dropped nearly its entire stockpile of publicly disclosed GBU-57s. The Defense Security Monitor estimates that the US now has fewer than six left.

Shockwaves Don’t Travel Far Enough

Blowing something up underground sounds dramatic, until physics gets involved. The assumption many outsiders make is that if a bunker-buster detonates near a target, the resulting shockwave will do the dirty work, rattling it to rubble. In reality, rock behaves less like a loudspeaker and more like a sponge.

The further a blast travels through solid earth, the more it fizzles out. Energy dissipates rapidly as the wavefront encounters seams, voids, and mineral inconsistencies. Each geological hiccup, whether it’s a crack in the bedrock or a change in density, saps more strength from the blast. Even the most ideal detonation starts to look like a bad handshake by the time it gets a few dozen meters into the mountain.

This attenuation problem only gets worse with depth. Fordo sits beneath a natural mountain ridge, nature’s own blast shield. The rock above is variable, fractured, and unpredictable. That variability blunts the bomb’s impact like a Kevlar vest for uranium centrifuges. You can create a decent surface-level explosion, sure, but by the time the pressure wave snakes its way toward the heart of the facility, it’s a whisper of what it was, barely enough to knock over a toolbox, let alone shred industrial machinery or rupture reinforced concrete walls.

That’s been validated in classified and open-source data. Underground nuclear tests during the Cold War, for example, showed how rapidly overpressure drops with distance in hard strata. A detonation has to occur frighteningly close to its target to guarantee destruction, often within a few meters. For Fordo, that’s the difference between a headline-making crater and a temporarily rattled operations room.

The Limits of Airpower, and the American Fantasy

There’s a reason military planners have a love-hate relationship with airpower. On paper, it looks clean, precise, and politically palatable, especially for democracies tired of body bags. Drop a high-tech bomb from 50,000 feet, roll the B-roll footage, and declare “mission accomplished” from the tarmac.

But reality is far messier.

The Fordo strike is a case study in this delusion. Fourteen bunker-busters from stealth bombers. A target buried beneath hundreds of feet of rock. No boots on the ground. No follow-up assault. Just the hope that gravity, kinetic energy, and a multi-million-dollar weapons package would do all the hard work. But hope is not a strategy, and airstrikes, even the big, headline-grabbing ones, rarely deliver strategic outcomes on their own... much to the chagrin of my colleagues in the Air Force

That’s because targets like Fordo are designed to withstand aerial punishment. Hardened facilities, buried bunkers, and dispersed command posts are textbook cases where precision munitions hit their limits.

You can rattle the walls, dent the door, and maybe even flood a tunnel, but you can’t confirm the kill unless you physically inspect the aftermath. That usually means someone with a rifle and a radio standing in the wreckage saying, “Yep, it’s gone.”

This is where the uncomfortable truth sets in: achieving military objectives often requires a combined arms approach. Don’t get me wrong, airpower is a vital component. It can shape the battlefield, degrade defenses, and neutralize threats, but it usually works best in concert with ground forces, special operations, cyber, and even good old-fashioned human intelligence.

Fordo didn’t need a bigger bomb. It needed someone to walk in and flip the light switches off manually. Now, I am in no way advocating for a ground invasion of Iran.

But America has long had a weakness for technological silver bullets. From drone strikes to precision-guided munitions to AI-enabled targeting, there’s a persistent fantasy that we can achieve complex political goals without ever getting our hands dirty.

It’s a seductive myth, not just for politicians looking to avoid domestic blowback, but for defense contractors who are all too happy to keep selling miracle machines that promise strategic effects without the bloodshed.

Bunker busters are profitable. $$$

Special forces raids with unpredictable outcomes? Less so. That’s why the cycle repeats: new threat, new tech, new contract. Rinse and repeat until someone points out that the enemy, remarkably, still has a functioning nuclear program.

So yes, airpower matters, but it’s rarely the whole answer. Sometimes, if you want to really end the threat, you have to send someone in to make sure the lights stay off for good.

Sometimes Dirt Wins

The GBU-57 is a marvel of modern engineering. But it’s still subject to the limits of material science, geology, and physics. Iran knew this. That’s why Fordo wasn’t just hidden, it was buried under 300 feet of rock, at a depth designed to laugh at even the most powerful non-nuclear penetrator.

If the DIA’s right, and if the bombs didn’t work as advertised, it’s not only a failure of the weapon, it’s a reality check. In this case, nature may have simply out-engineered the engineers.

Journalist Geoff Brumfiel has a great analysis of this in an X thread if you want a deeper dive into the math.

And as always, stay curious and stay skeptical.

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