The most dramatic missions of Operation Epic Fury were flown by the smallest fleet in the US Air Force. The B-2 Spirit stealth bomber, with only 20 airframes in existence, carried the only weapon capable of threatening Iran's deepest nuclear facilities: the GBU-57A/B Massive Ordnance Penetrator, a 30,000-pound bunker buster that represents the pinnacle of conventional penetrating munition design.
The Target Problem
Iran had learned from Israel's 1981 Osirak strike and the vulnerability of surface-level nuclear facilities. Beginning in the 2000s, Iran moved its most sensitive enrichment operations underground. The Fordow Fuel Enrichment Plant, located inside a mountain near Qom, was the ultimate hard target — buried under an estimated 80 meters of rock and earth, with multiple hardened access tunnels and blast doors.
Natanz, while partially above ground, housed its most advanced centrifuge cascades in underground halls reinforced with meters of concrete and earth overburden. Conventional 2,000-pound penetrating bombs like the GBU-28 could damage these facilities but lacked the kinetic energy to reach the deepest chambers. Only the GBU-57 had a realistic chance of penetrating to the target.
The Weapon: GBU-57A/B
Developed by Boeing under an Air Force program that began in 2004, the Massive Ordnance Penetrator is an engineering marvel designed for one purpose: destroying targets that nothing else can reach.
- Weight: 30,000 pounds (13,600 kg) — the heaviest conventional bomb in the US arsenal
- Length: 20.5 feet (6.25 m)
- Penetration: Up to 60 meters of earth or reinforced concrete (exact capability classified)
- Warhead: 5,300 pounds of high explosive, detonated after penetration
- Guidance: GPS/INS with hardened electronics that survive the deceleration of penetrating rock
- Unit cost: Approximately $3.5 million
The weapon uses its massive kinetic energy — delivered by a hardened steel penetrator case — to bore through layers of earth and concrete. The fuze is programmed to detonate only after the weapon has reached its target depth, maximizing destruction of the buried facility.
The B-2 Missions
B-2 sorties against Iranian nuclear facilities launched from Whiteman Air Force Base, Missouri — a round trip of approximately 25,000 miles requiring multiple aerial refueling sessions and 30+ hours of flight time. The 509th Bomb Wing maintained its combat-ready posture throughout the campaign, generating sorties at a pace rarely seen since the aircraft's introduction in 1997.
Each B-2 carried two GBU-57 MOPs in its internal weapons bays. The attack profile required precise GPS coordinates, and multiple weapons were directed at each aimpoint to ensure that sequential impacts deepened the penetration crater — a technique called "burrowing" where the second bomb follows the first through the same entry point to reach deeper.
The missions required extensive support: KC-135 and KC-46 tanker aircraft stationed along the route, EA-18G Growlers providing electronic warfare coverage over the target area, and F-22 Raptors flying escort to ensure no Iranian fighters threatened the bombers during their vulnerable weapons release phase.
Fordow: The Ultimate Test
The Fordow strike was the most technically challenging mission of Epic Fury. Intelligence assessments indicated that even the GBU-57 might not fully penetrate the mountain's depth to reach the enrichment halls. The attack plan called for multiple B-2 sorties delivering sequential MOP strikes on the same aimpoints, with each weapon deepening the penetration path created by its predecessor.
Post-strike satellite imagery showed massive debris plumes from the mountain's surface, and seismic monitoring stations detected the deep underground detonations. The initial battle damage assessment indicated "significant damage" to the facility, though the full extent of destruction to the deeply buried centrifuge halls could not be confirmed through overhead imagery alone.
Inventory Constraints
The GBU-57's extreme effectiveness came with a critical limitation: scarcity. With an estimated inventory of only 20-30 weapons, each MOP expenditure represented an irreplaceable capability loss. The Air Force had to balance achieving decisive damage to Fordow and Natanz against retaining a reserve for potential follow-up strikes or other contingencies.
This constraint influenced target planning throughout Epic Fury. Less hardened nuclear facilities at Isfahan and Arak were struck with conventional penetrating bombs — GBU-28s and GBU-31 JDAMs — reserving the precious MOP inventory exclusively for Fordow and Natanz. Even so, by the end of the initial nuclear strike campaign, the US had expended a significant fraction of its total MOP stockpile.
Strategic Impact
The B-2/MOP combination represented the ultimate expression of American conventional military power — the ability to hold any target on earth at risk, regardless of how deeply it was buried. The strikes on Fordow and Natanz set Iran's enrichment program back by years, destroying centrifuge cascades and contaminating underground spaces with rubble and radioactive debris that would take months to clear even if the facilities could be accessed. For the Pentagon, the missions validated a capability that had been developed over two decades specifically for this scenario. The B-2/MOP pairing remains the only conventional option for the world's deepest hardened targets — a capability no other nation possesses and one that the Air Force intends to preserve as the B-21 Raider enters service in coming years.