The 30,000-pound GBU-57 bombs, also known as MOPs, used in this assault were designed to attack deep underground targets in locations that are hundreds of feet below ground level. 

Caine and Defense Secretary Pete Hegseth briefed reporters at the Pentagon Thursday regarding the military’s planning and execution of the U.S. airstrikes on Iranian nuclear facilities, which marked the first-ever operational employment of the MOP weapon.

Early testing of the MOP began roughly two decades ago under a technology demonstration effort led by the Defense Threat Reduction Agency before being transitioned to the Air Force. Super computers were used for modeling and simulation during the development of the weapon, Caine noted during Thursday’s briefing. The chairman said he met yesterday with two DTRA officers who “spent their life’s work” enabling and demonstrating the complex bombs.

The U.S. used these so-called bunker-buster bombs on two nuclear facilities — in Fordow and Natanz — last weekend. Caine noted that the U.S. targeted ventilation shafts at Iran’s nuclear facility in Fordow.

The MOP is “comprised of steel, explosive and a fuze programmed bespokely [for] each weapon to achieve a particular effect inside the target. Each weapon had a unique desired impact, angle, arrival, final heading and a fuze setting. The fuze is effectively what tells the bomb when to function. A longer delay in a fuze, the deeper the weapon will penetrate and drive into the target,” he explained.

The U.S. military decided to strike two of the ventilation shafts at Fordow as the primary points of entry into the underground facility. In the days preceding the attack, the Iranians attempted to cover the shafts with concrete to try to thwart 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. 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 1000 feet per second and explode in the mission space,” he said. “There were six on each side. Weapons number six 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.”

Two additional MOPs were used on Natanz. A total of 14 were dropped during Midnight Hammer.

During a previous briefing on Sunday, Caine said that early battle damage assessments suggested that the “massive ordnance penetrator” bombs dropped by U.S. Air Force B-2 Spirit stealth bombers severely damaged Iran’s nuclear arsenal.

​​On Thursday, he said all of the MOPs used against Fordow went exactly where they were intended to go. 

“A bomb has three effects that causes damage: blast, fragmentation and overpressure. In this case, the primary kill mechanism in the mission space was a mix of overpressure 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,” he told reporters.

Hegseth criticized recent reporting about an intelligence assessment from the Defense Intelligence Agency in the wake of the attacks that suggested the airstrikes might not have damaged Iran’s nuclear program as much as senior Trump administration officials have claimed. Hegseth told reporters that there was “low confidence in this particular report.” 

Caine said the intelligence community is in charge of the battle damage assessments.

“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 function as designed, meaning they exploded. We know this through other means, intelligence means that we have,” Caine said. “We were visibly able to see them. And we know that the trailing jets saw the first weapons function, and the pilot stated, quote, ‘this was the brightest explosion that I’ve ever seen. It literally looked like daylight’” even though the attacks occurred in darkness.

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“The strike package was supported by U.S. Strategic Command, U.S. Transportation Command, U.S. Cyber Command, U.S. Space Command, U.S. Space Force and U.S. European command,” Gen. Dan Caine, chairman of the Joint Chiefs of Staff, told reporters in a briefing at the Pentagon Sunday morning, later thanking the cyber operators, among others, who made the mission possible.

However, no further details about Cybercom’s efforts were disclosed. The command referred DefenseScoop to the Pentagon for comment, where a spokesperson said they had nothing further to provide at this time beyond the transcript from Sunday’s press conference.

Although details about Cybercom’s assistance for Operation Midnight Hammer, the code name for the strikes, remain murky, experts — most of whom spoke to DefenseScoop on condition of anonymity — outlined a number of possibilities for how the organization may have contributed to the effort.

Outside experts noted that there probably aren’t any U.S. military ops nowadays, regardless of how rudimentary, where a cyber component isn’t involved.

“We really don’t do military operations without cyber support anymore,” Gary Brown, Cybercom’s first senior legal counsel and now a professor at Texas A&M’s Bush School of Government and Public Service, told DefenseScoop. “There is a cyber component for everything we do, even if it seems really unsophisticated, even if the cyber component is just on the intelligence collection side. It’s always there.”

Moreover, others pointed out that with such a high-profile operation, many Defense Department components will want involvement in order to prove their value.

A former military cyber official noted that a sophisticated operation like Midnight Hammer points to the maturation of Cybercom, which was created just 15 years ago and now is “is a fully integrated mechanism,” supporting air superiority and global transportation.

While details regarding Cybercom’s involvement in the strike were limited, experts provided a few examples for how the command could have supported such an attack. These sources noted that they had no inside knowledge of the recent operation and were largely speaking in hypothetical terms to offer vignettes for how digital forces would likely be involved in that type of mission.

The operation involved seven B-2 Spirit stealth bombers that dropped 14 “massive ordnance penetrators” — 30,000-pound so-called bunker-busting bombs — as well as Tomahawk missiles launched from a submarine and 125 aircraft that included refuelers and fighter jets, some of which were used as decoys to draw Iranian air defenses away from the B-2s. The strikes targeted the Iranian nuclear facilities at Fordow, Natanz and Esfahan.

Sources noted that this would probably be a broad effort from Cybercom across several of its elements spanning the defensive side, offensive side — through teams that support combatant commands — and possibly its elite Cyber National Mission Force that protects the nation from nation-state cyber activity.

The former official said one of the most likely ways Cybercom would have aided the operation is through something akin to a cyber escort package. With air assets coming from all over the world and various commands — such as Transportation Command, European Command, Central Command and the Air Force’s Global Strike Command — it is important to ensure those aircraft and enabling functions execute missions smoothly.

That includes backups and failsafes as well as ensuring the Department of Defense’s Information Network is up and running to enable communication. Defensive cyber protection teams would likely ensure infrastructure was up and running and protected from any adversary intrusions or disruptions. That could include teams supporting several combatant commands as well as those protecting the DOD Information Network and Transportation Command, headed by the DOD Cyber Defense Command.

One of the classic examples always cited throughout Cybecom’s history as a key capability for enabling military operations is the monitoring and disabling of enemy integrated air defense systems to allow friendly aircraft to penetrate and strike. If access is gained into those systems, cyber operators could turn them off or make them malfunction, preventing the enemy from shooting down friendly aircraft looking to engage targets.

Experts that spoke to DefenseScoop noted they had no direct knowledge if this was part of the strike package or capability over the weekend, but cited it as a potential example for how Cybercom could support a kinetic strike operation.

B-2 bombers rely on stealth and thus don’t have many defensives. Given that and the fact they’re not very maneuverable under fire, monitoring and possibly disabling an adversary’s IADS would be desirable to minimize the risk of the aircraft being shot down.

Others noted that any support Cybercom can offer often requires access ahead of time, a key caveat that is often overlooked. Unlike in Hollywood, cyberspace operations aren’t as easy as just pushing a button on a keyboard. Forces must be forward and present to gain the necessary access for intelligence collection to map and understand systems, and eventually affect systems if the go-ahead is given. Moreover, that access can be eliminated if forces are discovered by the target or if a patch is implemented.

Thus, cyber forces require constant persistence in order to gain and maintain those accesses, even during times outside of conflict. In 2018, Congress paved the way to enable the command to conduct this activity, referred to as intelligence preparation of the battlefield, without tipping the covert action statute that requires presidential authority to do so, clarifying cyber is a traditional military activity.

Given this access is difficult to gain and maintain, each operation requires an important calculus on whether to act on those implants and create effects because once used, that access is burned.

For example, if it wasn’t needed, the U.S. might not have acted on Iranian IADS if they weren’t poised to shoot down the B-2 bombers, provided this was part of the op.

Axios reported that the U.S. government asked Israel to eliminate Iranian air defense systems to clear a path for American aircraft.

Others pointed to how cyber operators could have been standing by to cause effects elsewhere to divert Iranian attention away from the targets. This could include brownouts or disrupting communications, though, again, those effects would likely be weighed against the downsides of giving up those accesses if those actions weren’t needed.

Cyber-enabled intelligence, surveillance and reconnaissance could have also been provided prior to the attack, producing targeting data, intelligence on Tehran’s likely immediate response, Iran’s force posture and ability to target U.S. forces during or right after the operation, according to sources.

Similarly, cyber forces could provide indications and warning during the attack to alert U.S. units with near real-time information on Iran’s military forces or counterattacks.

Support could also have taken the shape of offensive cyber action during the airstrikes, disabling Iranian military or civilian communications or their ability to respond, which likely would have been undertaken by combat mission teams that conduct cyber ops on behalf of combatant commands, mostly in the offensive sphere.

This activity could have disabled or disrupted enemy early warning systems or spoofed them in a way to show no activity incoming or many more assets moving in.

Sources also indicated cyber means could help with battle damage assessments after the strike, however, that would most likely fall within the purview of the NSA and its signals intelligence role, monitoring Iranian chatter and channels.

Some noted that it’s possible U.S. defense leaders were also lumping in NSA when they referred to the support of Cyber Command, both of which are co-located and share a leader despite having different missions — foreign intelligence, in the case of NSA.

In that vein, cyber forces, either from NSA or Cybercom, could’ve been monitoring for chatter among Iranian sources to see if they bit on the diversion the U.S. sought at the outset of the strikes against the nuclear facilities.

Defense officials reported that they sent some bombers initially west toward Guam as a ruse to distract from a potential strike in Iran, which was ultimately carried out by B-2s that flew east from the United States across the Atlantic to reach their targets.

There is also a defensive role Cybercom could be playing after the attack. Many experts are bracing for potential blowback in the digital domain and Iranian retaliation. While Tehran’s military has faced setbacks from Israeli attacks in recent days, it does pose a threat in cyberspace, which levels the playing field some as opposed to matching traditional forms of military might against the U.S. and Israel after having been significantly weakened.

Cybercom could be posturing and bolstering its capabilities to defend against threatening attempts against networks originating from Iran. This could take the form of a preemptive digital action against Iranian cyber capabilities to limit their capacity to conduct offensive retaliatory action. Forces standing by to support that role could be either combat mission teams focused on the Middle East region or Cyber National Mission Force teams assigned to specific Iranian threat actors poised to target the U.S. homeland in cyberspace.

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The event marked the first-ever operational employment of the weapon, Secretary of Defense Pete Hegseth confirmed Sunday during a press briefing at the Pentagon.

The 30,000-pound GBU-57 bomb, also known as the MOP, is designed to be capable of attacking underground targets. It can reportedly hit locations hundreds of feet below ground level.

“MOP is a large, GPS-guided, penetrating weapon with the ability to attack deeply-buried and hardened bunkers and tunnels. The warhead case is made from a special high‑performance steel alloy and its design allows for a large explosive payload while maintaining the integrity of the penetrator case during impact,” according to an Air Force description of the system.

Due to the bomb’s size and design, it can only be carried by the B-2 bomber. Each B-2 can carry two GBU-57s.

Early testing of the MOP began about 20 years ago under a technology demonstration effort led by the Defense Threat Reduction Agency before the technology was transitioned to an Air Force “quick reaction capability program,” according to a service fact sheet. Boeing was contracted in 2009 for MOP-aircraft integration efforts. In 2017, the MOP transitioned to an Air Force program of record, according to a report by the Pentagon’s director of operational test and evaluation.

Notably, in fiscal 2024, the Air Force conducted two full-scale tests to “verify fixes to a B-2 integration issue,” according to a DOT&E annual report.

The Air Force has been pursuing a MOP modification program to integrate a “smart fuze” capability into the weapon. The so-called Large Penetrator Smart Fuze is intended to provide “increased probability of kill” against hard and deeply buried targets “by mitigating the risk of target intelligence uncertainty,” according to the DOT&E report. Defense officials on Sunday did not say whether the MOPs used in Midnight Hammer were equipped with the smart fuze capability.

Seven B-2s and a variety of other assets were involved in Midnight Hammer, which included U.S. attacks on Fordow, Natanz and Esfahan in Iran, Gen. Dan Caine, chairman of the Joint Chiefs of Staff, told reporters at Sunday’s press briefing.

Hegseth said the aim of the mission, which was ordered by President Donald Trump, was to “destroy or severely degrade” Iran’s nuclear program. Western officials were concerned that the Iranian regime could use the country’s nuclear materials and know-how to build weapons of mass destruction.

“At approximately 6:40 p.m. Eastern Standard Time, 2:10 a.m. Iran time, the lead B-2 dropped two GBU-57 Massive Ordnance Penetrator weapons on the first of several aim points at Fordow,” Caine said. “The remaining bombers then hit their targets as well, with a total of 14 MOPs dropped against two nuclear target areas. All three Iranian nuclear infrastructure targets were struck between 6:40 p.m. and 7:05 p.m. Eastern time … with the Tomahawk missiles [launched from a submarine] being the last to strike at Esfahan to ensure we retain the element of surprise throughout the operation. Following weapons release, the Midnight Hammer strike package exited Iranian airspace, and the package began its return home.”

Fighter jets went in ahead of the bombers to guard against enemy fighter aircraft and surface-to-air missiles. The Defense Department is unaware of any shots being fired at the U.S. military aircraft on their way in or out of Iran, Caine noted.

About 75 precision guided weapons were employed during the operation, including the 14 MOPs, according to Caine.

Dozens of air refueling tankers were also involved in the mission, he noted, as well as intelligence, surveillance and reconnaissance aircraft, and hundreds of maintenance and operational personnel.

On Sunday evening, Trump posted on Truth Social that the B-2 pilots who took part in Midnight Hammer had safely returned to their base in Missouri. The mission from Whiteman Air Force Base to Iran and back lasted about 36 hours, with the help of aerial refueling, according to U.S. Strategic Command.

Senior U.S. officials touted the operation as a success.

“The damage to the Nuclear sites in Iran is said to be ‘monumental.’ The hits were hard and accurate. Great skill was shown by our military,” Trump said in a Truth Social post.

Hegseth described the mission as an “incredible and overwhelming success.”

Caine noted that a final battle damage assessment will take “some time” to complete. However, initial battle damage assessments “indicate that all three sites sustained extremely severe damage and destruction,” he told reporters.

Officials in the Trump administration over the weekend said they now hope to have a negotiated settlement to the conflict. They were waiting to see how Iran would respond.

On Monday, Iran launched missile attacks at a U.S. military base in Qatar.

“I can confirm that al Udeid Air Base was attacked by short-range and medium-range ballistic missiles originating from Iran today. At this time, there are no reports of U.S. casualties. We are monitoring this situation closely and will provide more information as it becomes available,” a U.S. defense official said in a statement.

Updated on June 23, 2025, at 2 PM: This story was updated to include comment from a U.S. defense official about an Iranian missile attack on al Udeid Air Base on Monday.

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