Few weapons in recent times have captivated—as much as provoked strategic concern—as the GBU-57 Massive Ordnance Penetrator, or MOP. In June 2025, this 30,000-pound bunker-buster was tested for the first time in combat as U.S. B-2 Spirit bombers assisted Israeli forces in strikes against Iran’s most heavily fortified nuclear sites. What occurred and why it matters is illuminated with respect to the new challenges of targeting deeply buried targets.
The Challenge of Iran’s Highly Buried Nuclear Facilities
Iran’s nuclear program has had to rely for years on underground cover to shield its most exposed activities. Experience from the 1981 Osirak reactor bombing in Iraq and the 2007 attack on Syria’s Al-Kibar facility forced Iranian engineers underground. Places like Fordow, which is beyond Qom, are hidden under hundreds of feet of rock and armored concrete, making conventional airstrikes virtually meaningless. The dispersal and depth of such sites forced military planners to rethink how to destroy hardened targets short of nuclear.
The Massive Ordnance Penetrator: Design and Capabilities
Enter the MOP. It weighs 30,000 pounds and is nearly 20 feet long, specifically geared to burrow through the concrete and rock strata to explode upon contact. Its steel shell focuses an appalling quantity of weight into a very small space, thereby able to act as a supersonic hammer. Released from an aerial B-2 Spirit, the bomb can reach speeds greater than Mach 1, delivering nearly a gigajoule of kinetic energy.
Having traveled through rock and reinforced concrete, its 5,300-pound explosive payload then explodes, and intelligent fusing causes it to only explode after traveling to the target’s farthest point. Only the B-2 is capable of carrying and delivering the MOP, and one bomber can transport two such massive ordnance units.
Operation Midnight Hammer: Execution and Outcomes
The United States first tested the MOP in combat in June 2025 under Operation Midnight Hammer. Seven B-2s, supported by aerial refueling tankers, fighter escort, and reconnaissance aircraft, set out from Whiteman Air Force Base to attack Iran’s most critical nuclear targets, Fordow, Natanz, and Esfahan. Fourteen bombs simultaneously attacked two target areas, coordinated with near-concurrent Tomahawk missile strikes on Esfahan for maximum surprise. The flights were round-trip flights that lasted approximately 36 hours, and all of the aircraft returned intact.
Initial estimates of damage showed widespread damage at all three targets. The attacks highlighted the MOP’s unique ability to penetrate and destroy deeply buried targets—something conventional ordnance could not accomplish. While the physical destruction was substantial, military analysts point out that the larger implications extend far beyond the initial damage.
Strategic and Geopolitical Implications
Fielding the MOP into combat is a turning point in counterproliferation policy. There were years of argument among planners about whether, or even if, it was feasible to destroy deeply buried nuclear plants without using nuclear weapons. This mission demonstrated that conventional weapons, with the right tools, could accomplish what was once impossible. The fact that only America has both the MOP and the B-2 serves to highlight the country’s unique capability in this regard. To friends, like Israel, collaboration with the U.S. remains essential for the operations of this high priority.
The strikes also delivered a message: buried sites are no longer invulnerable. But experts caution that destroying physical infrastructure doesn’t kill off expertise. Scientific know-how is still present in Iran, and therefore reconstruction is feasible, though costly and laborious.
Risks, Limitations, and the Road Ahead
Even as it appeared to succeed, the attack highlighted risks. Nuclear plant attacks hold the danger of radioactive spillage, though so far, contamination has been limited to localized areas. There is also the danger of escalation—in the aftermath of the attacks, Iran retaliated with missile attacks on Middle East-based U.S. bases, reminding planners that these operations never involve no risk.
The MOP is not a silver bullet. While it can blow up hardened targets, it does nothing to eliminate the underlying knowledge or ability of rivals. Counterproliferation efforts may deter, but they can also promote incentives to develop further hardened sites or underground programs. The operation shows the perpetual cat-and-mouse race of military technology: for every advance, there is an implied advance by potential rivals.
Ultimately, the first combat deployment of the Massive Ordnance Penetrator has reset the argument about deep-target attacks. It shows that when technology, planning, and execution are properly aligned, even the most heavily defended facilities can be threatened. It also reminds us, though, that military action is always an act of high-wire risk, capability, and calculated resolve—a one that will continue to evolve as the next generation of weapons and tactics unfold.