Everything We Just Learned About the Ordnance Penetrator Strikes on Iran

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The Pentagon has shared extensive new information about the use of 30,000-pound GBU-57/B Massive Ordnance Penetrator (MOP) bunker buster bombs in recent strikes on Iran, a mission it says was 15 years in the making. Additional details have also been provided about how the specific need to hold the deeply buried Iranian enrichment facility at Fordow at risk was a primary design driver for the MOP program and its evolution. All of this comes amid still evolving and often competing assessments, at least from what we know so far, about what the strikes on Iran actually achieved.

Chairman of the Joint Chiefs of Staff U.S. Air Force Gen. Dan “Razin” Caine talked extensively about the GBU-57/B’s development and its employment in strikes on Iran this past weekend, dubbed Operation Midnight Hammer, at a press conference at the Pentagon today. Caine spoke to TWZ and other outlets alongside Secretary of Defense Pete Hegseth. The Pentagon previously disclosed that B-2 stealth bombers dropped 12 MOPs on Fordow and another two on an underground portion of the Iranian nuclear facility at Natanz during the mission. Targets on the surface at the Iranian nuclear site Isfahan were struck separately by Tomahawk land-attack cruise missiles launched from a U.S. Navy submarine.

“The GBU-57/B, which all of you I know know [sic], is a 30,000-pound weapon dropped only by the B-2. It’s comprised of steel, explosive, and a fuze,” Caine said. For the actual strike on Fordow this past weekend, the MOPs each had their “fuze programmed bespokely” in order for “each weapon to achieve a particular effect inside the target,” and that each of the 12 bombs “had a unique, desired impact angle, arrival, [and] final heading,” he explained.

A pair of ventilation shafts, with their openings above ground, were the primary targets, something that sounds right out of a Hollywood blockbuster, like the first Star Wars movie or, more recently, Top Gun: Maverick.

“In the days preceding the attack against Fordow, the Iranians attempted to cover the shafts with concrete to try to prevent an attack,” according to Caine. “I won’t share the specific dimensions of the concrete cap, but you should know that we know what the dimensions of those concrete caps were. The planners had to account for this. They accounted for everything.”

Earlier this week, TWZ explored in great detail evidence of Iranian efforts to seal up Fordow against a potential ground raid in the days leading up to the Operation Midnight Hammer strikes, which you can find here. Capping the ventilation shafts would also have denied another potential access point to any forces on the ground.

In the end, six MOPs were dropped on each of the two shafts at Fordow, with both groups of munitions being employed in the same general fashion, Caine further explained.

“The cap was forcibly removed by the first weapon, and the main shaft was uncovered. Weapons two, three, four, [and] five were tasked to enter the main shaft, move down into the complex at greater than 1,000 feet per second, and explode in the mission space,” Caine continued. The sixth bomb in each group “was designed as a flex weapon to allow us to cover if one of the preceding jets or one of the preceding weapons did not work.”

“All six weapons at each vent at Fordow went exactly where they were intended to go,” according to the Chairman of the Joint Chiefs of Staff. “A bomb has three effects that causes [sic] damage: blast, fragmentation, and over-pressure. In this case, the primary kill mechanism in the mission space was a mix of over-pressure and blast ripping through the open tunnels and destroying critical hardware. The majority of the damage we assess, based on our extensive modeling, was a blast layer combined with the impulse extending from the shock. “

“A point that I want to make here, the Joint Force does not do BDA [bomb damage assessment] by design, we don’t grade our own homework. The intelligence community does,” Caine noted. “But here’s what we know following the attacks and the strikes on Fordow. First, that the weapons were built, tested, and loaded properly. Two, the weapons were released on speed and on parameters. Three, the weapons all guided to their intended targets and to their intended aim points. Four, the weapons functioned as designed, meaning they exploded.”

“The pilots stated, quote, ‘this was the brightest explosion that I’ve ever seen. It literally looked like daylight,'” according to Caine.

Caine’s comments confirm much of TWZ‘s previous analysis of the Operation Midnight Hammer strikes, as well as the general employment methodology for the MOP, including using multiple bombs to drill down on a single point of impact.

Caine also took time today to explain how the need to strike Fordow, in particular, was a key aspect in the GBU-57/B MOP’s development, and shared videos from past testing of the munition, seen below.

“There’s an organization in the U.S. called the Defense Threat Reduction Agency, DTRA. DTRA does a lot of things for our nation, but DTRA is the world’s leading expert on deeply buried, underground targets,” Caine said by way of introduction into his remarks about the MOP. “In 2009, a Defense Threat Reduction Agency officer was brought into a vault at an undisclosed location and briefed on something going on in Iran for security purposes. I’m not going to share his name.”

“He was shown some photos and some highly classified intelligence of what looked like a major construction project in the mountains of Iran. He was tasked to study this facility, [and] work with the intelligence community to understand it, and he was soon joined by an additional teammate,” Caine continued. “For more than 15 years, this officer and his teammate lived and breathed this single target, Fordow, a critical element of Iran’s covert nuclear weapons program. He studied the geology. He watched the Iranians dig it out. He watched the construction, the weather, the discard material, the geology, the construction materials, where the materials came from. He looked at the vent shaft, the exhaust shaft, the electrical systems, the environmental control systems, every nook, every crater, every piece of equipment going in and every piece of equipment going out.”

“They literally dreamed about this target at night, when they slept,” he added. “They thought about it driving back and forth to work, and they knew from the very first days what this was for. You do not build a multi-layered underground bunker complex with centrifuges and other equipment in a mountain for any peaceful purpose.”

“Along the way, they realized we did not have a weapon that could adequately strike and kill this target,” according to Caine. “So they began a journey to work with industry and other tacticians to develop the GBU-57.”

It is important to note here that DTRA had already been working on what became known as the GBU-57/B for years before 2009, as part of a larger Hard Target Defeat (HTD) program. However, the MOP did not begin to enter operational service until the early 2010s, after Caine said being able to strike Fordow had emerged as a central factor in the munition’s development. The design has been upgraded multiple times since then. The chairman also made clear today that the U.S. intelligence community had been aware of work at Fordow prior to 2009, when he says the individuals at DTRA were tasked to focus their efforts on it. Work on Fordow is understood to have first started in 2006.

“They tested it [the MOP] over and over again, tried different options, tried more after that. They accomplished hundreds of test shots and dropped many full-scale weapons against extremely realistic targets for a single purpose: kill this target at the time and place of our nation’s choosing,” Caine said. “Ultimately, weaponeering is determining the right weapon and fuse combination to achieve the desired effects and maximum destruction against a target. In the case of Fordow, the DTRA team understood, with a high degree of confidence, the elements of the target required to kill its functions, and the weapons were designed, planned, and delivered to ensure that they achieve the effects in the mission space.”

MOP testing is already known to have occurred at various locations within the U.S. Army’s White Sands Missile Range in New Mexico.

Me, standing at the edge of a MOP crater on a mountain top at White Sands Test Range, where detailed studies of massive earth penetrators were studied for effectiveness against deeply buried targets by the Defense Threat Reduction Agency (DTRA) —formerly Defense Nuclear Agency.… pic.twitter.com/JYq1V2xO6q

— Gary Stradling (@gary_stradling) June 24, 2025

The US military has been understandably reluctant to share detailed information about live tests of the MOP. However, several press releases do mention that MOP tests took place at White Sands Missile Range (WSMR) in New Mexico. 2/10 pic.twitter.com/oQSdxJVQ7g

— Fabian Hinz (@fab_hinz) June 25, 2025

“By the way, 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,” Caine noted today.

“Then, on a day in June of 2025, more than 15 years after they started their life’s work, the phone rang and the President of the United States ordered the B-2 force that you’ve supported to go strike and kill this target,” the Chairman of the Joint Chiefs of Staff added. Caine said he met in person yesterday with the two members of DTRA in question.

Significant questions do still remain about the exact results of the Operation Midnight Hammer strikes. The leak of an initial intelligence report suggesting that damage to Fordow, specifically, was minimal, directly prompted today’s press briefing. By the end of yesterday, Hegseth and several other senior U.S. government officials had already made statements saying that confidence in the initial report was low and/or that additional intelligence had led to updated assessments of more significant damage to the site. You can read more about all of this in our previous reporting.

How the damage to Fordow, as well as to Natanz and Isfahan, will impact future nuclear developments in Iran remains to be seen. Iran’s parliament approved a bill yesterday to cease all cooperation with the International Atomic Energy Agency (IAEA).

Hegseth said at today’s press briefing that the “mission set back a nuclear program in ways that other presidents would [only] have dreamed,” but did not elaborate. He did refer back to statements put out yesterday by the Central Intelligence Agency (CIA) and the Israel Atomic Energy Commission (IAEC) that Fordow had been functionally destroyed and would require significant effort to rebuild.

“Of course, our IC, the intelligence community, will keep watching what Iran does and pay attention to that,” Hegseth added.

When it comes to GBU-57/B, the Air Force is also working now toward a successor to that munition, which you can read more about here. Just like the emergence of Fordow impacted MOP’s original development, it is hard not to see post-strike assessments from Operation Midnight Hammer feeding into what is currently referred to as the Next Generation Penetrator (NGP).

“You know, one of the things that I’m trying to do through this journey that we’re on together, of course, [is] transparency, but also the requirement to really protect these capabilities,” Caine said today. “So there’s a balance in there, right. We do need to preserve options, should the nation and the joint force be tasked to go do something again. So I’m confident we’ll find the middle ground. But there are some things that have passed [that] I want to not release for later.”

Regardless, Operation Midnight Hammer has prompted the disclosure of significant and fascinating new details about the MOP and its history.

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