On Saturday, June 21, 2025, following a spate of unprecedented aerial attacks that Israel carried out against Iran just days before, the United States joined the war and used bunker-busting bombs to strike three key Iranian nuclear sites and their underground bunkers: the Fordow fuel-enrichment plant, the Natanz nuclear facility, and the Isfahan nuclear technology center.
Operation Midnight Hammer, the Pentagon’s codename for the strikes on Iran, marks the first-ever use of the Massive Ordnance Penetrator (MOP), a colossal 30,000-pound bomb that only the B-2 stealth bomber can carry. As such, America has been regarded as the only country capable of taking out Iran’s underground nuclear facilities, and therefore its nuclear program—but if it actually accomplished that feat is yet to be seen.
While President Trump declared that the operation “completely and totally obliterated” the sites, Iranian officials downplayed the attacks. As of publication time, it’s unclear the level of damage inflicted based on satellite imagery alone, but a CNN report published on Tuesday afternoon claims that the strikes on Iran did not destroy the country’s nuclear program and has instead only set it back by a matter of months, according to early U.S. intelligence.
If history serves as any indication, there is a chance Iran’s underground nuclear facilities could be partially or wholly intact. That’s because up until now, in the quiet arms race between concrete and bombs, the concrete has been winning.
In the late 2000s, for instance, rumors circulated about a bunker in Iran struck by a bunker-buster bomb. The bomb had failed to penetrate—and remained embedded in—the surface of the bunker, presumably until the occupants called in a bomb-disposal team. Rather than smashing through the concrete, the bomb had been unexpectedly stopped dead. The reason was not hard to guess: Iran was a leader in the new technology of Ultra High Performance Concrete , or UHPC, and its latest concrete advancements were evidently too much for standard bunker busters.
Stephanie Barnett, Ph.D, of the University of Portsmouth in the U.K. is involved in developing stronger concrete to protect civilian buildings from terrorist attacks, and has heard about Iran and its ultra-tough concrete. While civilian audiences have been enthusiastic about the advancements in concrete, she occasionally hears less positive responses from military personnel attending her presentations.
“One officer told me, ‘If you make this stronger blast- and impact-resistant material, we need to think about how to get through it,’” Barnett says.
Getty Images On June 21, 2025, the U.S. Air Force used six B-2 bombers to drop 12 bunker-busting bombs on Fordow, Iran’s most significant nuclear enrichment facility, an official told CNN. Based on satellite imagery alone, it’s still unclear the level of damage the underground bunker sustained.
The U.S. Air Force introduced its first modern bunker buster in 1985. General-purpose bombs have a thin steel casing filled with explosives, while bunker busters have a narrower profile, with a thicker casing and less explosives. This design concentrates all the weight on a smaller area, making it an ice pick rather than a hammer, so the bomb can smash through concrete or burrow through earth to strike deeply-buried targets.
While the same general-purpose bombs from the 1990s are being used today, bunker busters had to go through several generations of upgrades. In the early 2000s, the Air Force even developed a special type of steel for the purpose, known as , in association with steel specialist Ellwood National Forge Company.
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