Why America’s giant bunker-busting bombs may have failed to reach their target : NPR

An American Air Force B-2 spirit is prepared for operations before “Operation Midnight Hammer” to Whiteman Air Force Base, Missouri, June 2025.

509th Wing / Digital Bomb

hide

tilting legend

509th Wing / Digital Bomb

Infographics were everywhere as Sunday’s morning strike approaches Iranian nuclear installations by American stealth bombers.

They represented the American bunker bomb, known as the massive ammunition or GBU-57 penetrator. He had fallen from above above the earth by a B-2 bomber. Then, the graphics showed it plowing a narrow channel deeply under the ground – about 60 meters, or 200 feet – and radiant in an illustrated explosion.

Only America had this 30,000 pound weapon. Only America could strike the most buried Uranium enrichment site in Iran in a place called Fordo. It was buried under almost 90 meters (about 300 feet) of rock, much deeper than the Israeli bombs could not penetrate.

There was only one problem – I was not entirely sure that it would work.

Now it seems that it may not be. According to an evaluation still classified by the Defense Intelligence Agency, the bombs did not “erase” the Iran enrichment site of Iran, as President Trump said. Instead, this has only made damage limited to the advanced centrifuges that remained there. At most, the program was set back “a few months”, according to an American official who confirmed the existence of the assessment at NPR but remained anonymous because they were not allowed to speak to the press.

The White House disputes this assertion.

“The flight of this alleged evaluation is a clear attempt to lower President Trump,” said the press secretary of the White House, Karoline Leavitt, on the social media platform X. “Everyone knows what is happening when you deposit fourteen bombs of 30,000 pounds perfectly on their objectives: total obtaining.”

Well … not necessarily.

Decades ago, I covered another effort to create a powerful weapon penetrating by the earth. In the aftermath of September 11, with an eye towards the caves of Afghanistan, where Osama bin Laden was supposed to hide, the administration of the president of George W. Bush examined if a nuclear weapon could be placed from an airplane in the ground. The robust penetrating nuclear earth, as the concept was known, would provide a powerful shock to tunnels and underground bunkers.

But when scientists got involved, they discovered that there was no way to obtain a nuclear weapon almost deep enough to contain the explosion and radioactive benefits, and the program was finally abandoned.

I went back to take a look at the mathematics of these first studies, and I found that it was actually quite simple. The equations have existed since the 1960s and depend on a limited number of factors, including the shape of the nosecon, the weight and the diameter of the weapon, the speed at which it touches the soil and – especially – the type of earth on which it is falling.

“It depends a lot on the type of rock,” explains Raymond Jeanloz, professor at the University of California in Berkley and one of the original authors of the national study of the 2005 academies on land penetrators.

When I executed the calculations, using a key equation of this study, I discovered that the GBU-57 could go up to 80 meters (262 feet) underground if it had fallen into the silt clay.

In the average rock, things seemed very different. The GBU -57 could only do about 7.9 meters (about 25 feet) under the ground – well below the 60 meters claimed by the infographic.

This can be an important part of the reason why the weapon failed to destroy its objective – if indeed the bombs have failed as DIA claims.

Jeanloz says it is not only the strength of the rock. Changes in the geological structure can also bring the bomb to change the direction even when it moves through the earth.

“If there are variations … including fractures or gaps, which can divert the trajectory in the soil,” he said. These same variations can disperse any explosion of the bomb.

It is clear that American planners were aware of this type of challenges. Rather than sending one or two GBU-57, they sent 12 to fall on Fordo. Based on satellite imaging, it seems that they may have been fell by pairs, the first weapon fracturing the rock to increase the penetrating depth of the second. The bombers also seemed to target the Fordo ventilation system, a possible weak point.

The weapons have probably created a powerful shock wave in the rock which would have traveled deeply underground, wrapping the installation below.

But Jeanloz says that these shock waves weaken quickly when they move into the rock. Fordo’s position directly under the crest of the mountain has probably maximized this protection.

In fact, going further is a simple solution to the threat of bunker-buses. A major conclusion of the 2005 study was: “It is cheaper and easier for someone to dig more deeply than to penetrate through this depth,” he said.

It turns out that geology may have thwarted one of the most daring American air operations in recent memory.

Tom Bowman of NPR has contributed to this report.