B-2 stealth bombers, 6 ‘bunker busters'—how US strikes on Iran unfolded
This article delves into the details of the strike, the targeted sites, the B-2 bomber, the MOP weapon, comparable munitions, and the potential damage inflicted.
On 22 June at 0230 hours (2.30 am) local time in Iran, the United States Air Force (USAF) dropped bombs on three key Iranian nuclear facilities: Fordow, Natanz, and Isfahan. The operation, described by President Donald Trump as a 'spectacular success', marked the first combat use of the GBU-57 Massive Ordnance Penetrator (MOP) and showcased the unparalleled capabilities of the B-2 Spirit stealth bomber.
As President Donald Trump gave Iran a two-week deadline on 19 June, the world expected diplomacy to play out for some more time. A mere two days later, he ordered the United States Air Force to bomb Iran.
Attack profile
The airstrike was carried out by a formation of B-2 Spirit stealth bombers, departing from Whiteman Air Force Base in Missouri. The bombers flew over 40 hours to Fordow in a round-trip mission. The likely route involved a trans-Pacific flight and was supported by multiple mid-air refuellings by KC-135 Stratotanker aircraft.
Surprisingly, the movement of the B-2 bombers and the Stratotankers was being widely reported on X. Despite the obvious loss of surprise, the formation executed the mission without any significant interference from the Iranians. The approach over Iran was made from the Arabian Sea, from vectors where SEAD/DEAD (Suppression/Destruction of Enemy Air Defences) operations had already degraded Iranian air defence significantly. It must be noted that Israel had executed these SEAD missions as part of Operation Rising Lion, launched on 13 June.
The attack profile used the B-2's stealth capabilities: the aircraft can fly at approximately 50,000 feet (15,240 metres) and a speed of about 0.95 Mach (1173.06 kilometres per hour) to evade detection. Each B-2 bomber deployed carried two 30,000-pound (13,600 kilograms) GBU-57 MOP bombs.
A US official confirmed that GBU-57s were dropped on Fordow and Natanz, six of them at the former site, which is more fortified. These strikes were also reportedly aided by submarine-launched Tomahawk Land Attack Missiles (TLAMs) at Natanz and Isfahan. Since the GBU-57 is essentially a 'gravity' bomb, the attack profile required the B-2s to fly close to the targets, exposing them to potential residual Iranian defences. The launch had to be made from within a precise 'bucket', requiring accurate piloting during the attack run.
Also read: Iran's brutal regime is facing a reckoning. Consequences of US attack will go beyond Tehran
Nuclear sites targeted
1. Fordow
Anticipating an aerial attack from specialist weapons, the Iranians constructed a facility 300 feet (91 metres) beneath a mountain near Qom, called the Fordow Fuel Enrichment Plant. It is Iran's most fortified nuclear enrichment facility. Built into a cave complex and reinforced with layers of concrete, it is designed to withstand conventional attacks.
Fordow is protected by Russian-supplied air defence systems, though Israeli strikes had significantly degraded those to a level not considered threatening. The facility is critical to Iran's nuclear programme, with the International Atomic Energy Agency (IAEA) reporting in May 2025 that Fordow was enriching uranium to 60 per cent purity, taking it closer to the levels required for nuclear weapons.
The site's depth and hardening posed a unique challenge. The only weapon that could possibly strike targets that deep was the GBU-57 MOP. Reportedly, the MOP can penetrate up to 200 feet (61 metres) of rock or concrete, requiring multiple hits at the same point to breach 300 feet of rock.
2. Natanz
Natanz is Iran's oldest, largest, and most widely known uranium enrichment site. It features both underground as well as above-ground structures. The underground complex is not very deep, likely buried at only 20-30 feet (6-9 metres).
While less fortified than Fordow, Natanz's underground centrifuges are critical to Iran's nuclear ambitions. Israeli strikes on 12 June, as part of the opening wave of Operation Rising Lion, damaged surface infrastructure. While the underground structures were targeted, the damage remains unknown.
It made operational sense to strike this site again. The US used the GBU–57 and the Tomahawk missiles to ensure comprehensive destruction.
3. Isfahan
The Isfahan nuclear research facility, less hardened than Fordow or Natanz, supports Iran's nuclear fuel cycle and research activities. The facility housed a Uranium Conversion Facility (UCF), which converts uranium ore concentrate (yellowcake) into uranium hexafluoride (UF6), a gaseous form used for enrichment, and uranium oxide (UO2), used in nuclear fuel production.
Incidentally, the enriched uranium at this site was kept under IAEA safeguards. It was struck primarily with the Tomahawks, targeting surface infrastructure. While not a primary enrichment site, Isfahan's role in Iran's nuclear programme made it a strategic target in disrupting Tehran's broader capabilities.
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B-2 Spirit stealth bomber
The B-2 Spirit, developed by Northrop Grumman, is the USAF's premier stealth bomber, designed to penetrate sophisticated air defences and deliver precision strikes. The first operational aircraft, named 'Spirit of Missouri', was delivered to Whiteman Air Force Base, Missouri, in December 1993. The total programme cost for 21 B-2 bombers was approximately $45 billion. The B-2's flying-wing design, advanced stealth technology, and significantly large bomb bay made it an ideal platform for this high-risk mission.
The B-2 has a range of over 6,000 nautical miles without refuelling, which is extendable to global reach with aerial refuelling. Its internal weapons bays, originally designed for 20,000-pound (9,000 kilograms) payloads, were modified to accommodate two 30,000-pound MOPs.
The operating costs for B-2 bombers are substantial, estimated at $135,000 per flight hour, with maintenance requiring specialised facilities. The B-2's ability to carry nuclear and conventional munitions, including the B83 nuclear bomb and Joint Direct Attack Munitions (JDAMs), underscores its versatility.
Crew preparation
The B-2 Spirit is manned by a two-person crew, consisting of a pilot and mission commander. The crew would have meticulously prepared for this 40-hour mission over Iran.
Preparing for an operation such as this typically involves extensive briefings on intelligence, flight routes, targets, and contingencies, alongside likely threats. For some complex missions, the crew would fly in a simulator before undertaking the live mission.
Crew members make sure they're well-rested before an operation. During the long flight, they manage to rest by alternating naps in a designated area, using noise-cancelling headsets. Cockpit ergonomics and psychological training help mitigate stress.
It must be noted that mental robustness is a key crew selection criterion for a B–2 crew member. They must be well-versed in precise navigation, real-time threat monitoring, and weapons deployment. They may also use approved stimulants like modafinil to enhance alertness, under strict medical oversight, ensuring sustained performance throughout the gruelling mission.
The crew members probably breathed easy only after they exited Iranian airspace.
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GBU-57 Massive Ordnance Penetrator
The GBU-57 MOP, developed after the 2003 Iraq War by the Defense Threat Reduction Agency (DTRA), Air Force Research Laboratory (AFRL), and Boeing, is the USAF's most powerful non-nuclear bomb. Designed to destroy deeply buried and hardened targets, it underwent testing from 2007 to 2011, with improvements in fuzing for controlled explosions in confined spaces.
The MOP carries a 5,300-pound (2,404 kilograms) warhead of AFX-757 and PBXN-114 explosives. Encased in a high-performance steel alloy, the bomb can penetrate up to 200 feet before detonation. Soil penetration depends on the speed of impact and the composition of the surface.
The 20.5-foot-long (6.2 metres) bomb is guided by GPS and an Inertial Navigation Unit (INU), ensuring precision. Each MOP costs approximately $20 million, reflecting its specialised design. Only the B-2 is certified to carry the MOP; the B-52 was tested but not cleared. The unmanned B-21 Raider is being prepared for future use. Israel lacks both the MOP and a compatible platform for it, necessitating US involvement.
Comparable weapons
1. B61-11 Nuclear Bomb
The B61-11 is a low-to-intermediate yield nuclear weapon in the US arsenal. It was designed specifically for bunker-busting missions to destroy hardened, deeply buried targets such as command bunkers or underground facilities. However, the use of a nuclear weapon carries significant environmental risks besides severe geopolitical ramifications.
2. GBU-43/B MOAB
The GBU-43/B MOAB (Massive Ordnance Air Blast), nicknamed the 'Mother of All Bombs', is primarily a thermobaric weapon that uses atmospheric oxygen to create a massive blast wave and intense heat. This bomb is released from an MC-130E Combat Talon or a similar cargo aircraft like the C-130, using a drogue parachute to stabilise descent. Unlike the GBU-57 MOP, it is not carried by bombers like the B-2 Spirit.
There is only one known use of this bomb. On 13 April 2017, a single GBU 43 was used against an Islamic State: the Khorasan Province (ISIS-K) tunnel complex in Achin District, in Afghanistan. Dropped by an MC-130, it achieved mixed results. The results were not found commensurate with the strategic risk of collateral damage and the high cost of the weapon.
3. FOAB
Not to be left behind by the media attention garnered by the 'Mother of All Bombs', Russia tested its own thermobaric weapon, calling it FOAB (Father of All Bombs). Tested in 2007, the Russians claimed four times more destructive power than the MOAB. Its specifications are disputed, and it lacks the MOP's penetration capability, limiting its relevance to hardened targets.
4. Grand Slam
The Grand Slam, officially designated as the 'Bomb, Medium Capacity, 22,000 lb', was a massive conventional bomb developed by the British Royal Air Force (RAF) during World War 2. It was one of the largest and most powerful weapons used in the war, designed as an 'earthquake bomb' to destroy heavily fortified or underground targets by creating shockwaves through the ground. It was used to target hardened German infrastructure.
Damage assessment
President Trump claimed the strikes 'completely and totally obliterated' Iran's nuclear facilities. The facilities at Natanz and Isfahan likely suffered significant damage from the Tomahawks, but credible battle damage assessment (BDA) is pending.
Satellite imagery from Maxar depicted 'unusual truck and vehicular activity' at Fordow before the attack, suggesting Iran may have moved critical assets. Appearing on state-run TV, the deputy political director of Iran's state broadcaster, Hassan Abedini, said that the country 'didn't suffer a major blow because the materials had already been taken out'.
Intelligence and defence analysts suggest that the strikes set Iran's nuclear programme back by years, but did not eliminate its knowledge base. The fate of approximately 400 kilograms of highly enriched uranium kept at Isfahan is also unknown. The operation's success hinges on whether Fordow's enrichment capabilities were disabled—a question that awaits further intelligence and imagery analysis.
Also read: US strikes on Iranian nuclear sites draw Israel's praise, China calls it 'repeat of Iraq mistake'
Radiological fallout
The IAEA released a statement following the strikes on X.
'Following attacks on three nuclear sites in Iran – including Fordow – the IAEA can confirm that no increase in off-site radiation levels has been reported as of this time. IAEA will provide further assessments on situation in Iran as more information becomes available,' the post read.
This statement does not offer any proof of the success or failure of the mission. What it does tell us is that enriched uranium was not directly hit.
The airstrikes undertaken by the B-2 bombers on Iran's nuclear sites were a bold demonstration of US military power. The unique capability presented by the MOP takes away the concept of safe sanctuary and hardening of targets. With each B-2 costing over $2 billion, however, one cannot forget that such capabilities come at an immense cost.
Group Captain Ajay Ahlawat is a retired IAF fighter pilot. He tweets @Ahlawat2012. Views are personal.
(Edited by Prasanna Bachchhav)
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