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In a dramatic turn in West Asia’s escalating crisis, the United States has deployed one of its most formidable weapons—the GBU-57 Massive Ordnance Penetrator (MOP)—in direct strikes on Iran’s underground nuclear facilities. But what is this weapon, and why was it considered essential to this operation?
What Is the GBU-57 MOP?
The GBU-57A/B Massive Ordnance Penetrator—commonly known as the MOP—is the most powerful non-nuclear bomb in the US arsenal designed specifically to destroy deeply buried and fortified targets.
- Weight: Over 13,600 kilograms (30,000 pounds)
- Length: Nearly 6.2 meters (20.5 feet)
- Penetration Capacity: Can burrow through 60 meters of reinforced concrete or several hundred feet of earth before detonating.
- Purpose: Tailored to target hardened underground bunkers, particularly those used for storing weapons of mass destruction or protecting high-value military assets.
Developed by Boeing and fielded by the US Air Force, the MOP is delivered by heavy stealth bombers, such as the B-2 Spirit, which are capable of flying undetected into hostile airspace.
Why Was It Used on Iranian Nuclear Facilities?
Iran’s nuclear infrastructure has long been designed with maximum survivability in mind. Facilities like Fordow, Natanz, and Isfahan are heavily fortified—some are buried deep within mountains or shielded beneath layers of reinforced concrete, making them nearly impervious to conventional airstrikes.
- Fordow Fuel Enrichment Plant: Dug into a mountain near Qom, heavily protected and a known uranium enrichment centre.
Iran’s nuclear facility at Fordow is located approximately 100 km (60 miles) southwest of Tehran. While it also contains centrifuge cascades, it is smaller than the facility at Natanz. According to the International Atomic Energy Agency (IAEA), construction of Fordow began at least as early as 2007. However, Iran only informed the UN nuclear watchdog about its existence in 2009, after US and allied Western intelligence agencies became aware of it.
The facility is buried under a mountain and is protected by anti-aircraft batteries, indicating that it is designed to withstand air strikes. Military experts believe that it could only be targeted effectively by bunker-buster bombs, which are designed to penetrate deep below the surface before detonating. One such example is the GBU-57 A/B Massive Ordnance Penetrator, a precision-guided bomb weighing approximately 13,600 kg, intended for attacking deeply buried and hardened bunkers and tunnels.
- Natanz: A sprawling underground facility central to Iran’s centrifuge operations.
Iran’s nuclear facility at Natanz, located approximately 220 km (135 miles) southeast of Tehran, serves as the country’s primary site for uranium enrichment. Israeli airstrikes have already targeted this facility. The uranium at Natanz has been enriched to levels of up to 60 per cent purity, which is considered mildly radioactive but is just a short step away from weapons-grade material. Following an Israeli attack, the above ground portion of the facility was destroyed, as reported by the UN’s nuclear watchdog, the International Atomic Energy Agency (IAEA).
Another part of the facility is situated underground on Iran’s Central Plateau to protect against potential airstrikes. This section operates multiple cascades—groups of centrifuges working together to accelerate the uranium enrichment process. The IAEA believes that most, if not all, of these centrifuges were destroyed in the Israeli strike that cut off power to the site.
The IAEA has stated that the contamination resulting from these strikes was limited to the facility itself and did not affect the surrounding area. Additionally, Iran has been drilling into the Kūh-e Kolang Gaz Lā, also known as Pickax Mountain, which is located just beyond the southern perimeter of Natanz. The facility had previously been targeted by the Stuxnet virus, which is believed to have been created by Israeli and American entities, and that virus successfully destroyed Iranian centrifuges. Furthermore, two separate attacks, attributed to Israel, have also hit the facility.
- Isfahan: Known for uranium conversion, vital to feeding enrichment processes.
The facility in Isfahan, located about 350 km (215 miles) southeast of Tehran, employs thousands of nuclear scientists. It also houses three Chinese research reactors and laboratories that are part of the country’s atomic program.
Israel has targeted buildings at the Isfahan nuclear site, including a uranium conversion facility. However, the International Atomic Energy Agency (IAEA) has reported no signs of increased radiation at the site.
- Other nuclear sites
Iran has several other locations involved in its nuclear program that were not included in the recent US strikes. The country’s only commercial nuclear power plant is located in Bushehr, about 750 km (465 miles) south of Tehran. Iran is also constructing two additional reactors at this site. The Bushehr plant is fueled by uranium sourced from Russia, not Iran, and is monitored by the IAEA.
The Arak heavy water reactor is situated 250 km (155 miles) southwest of Tehran. While heavy water helps cool nuclear reactors, it also produces plutonium as a by-product, which can potentially be used in nuclear weapons. Under the 2015 nuclear deal with world powers, Iran agreed to redesign the facility to address concerns about proliferation.
The Tehran Research Reactor is located at the headquarters of the Atomic Energy Organization of Iran, the civilian agency overseeing the country’s atomic program. Initially, this reactor required highly enriched uranium, but it was later retrofitted to use low-enriched uranium due to concerns about proliferation.
These sites are considered core to Iran’s nuclear capabilities and have been monitored closely by Western intelligence for years.
The Strategic Message Behind the Strike
The U.S. decision to deploy MOPs in a pre-emptive strike signal both technical capability and strategic intent. Unlike symbolic airstrikes, the use of the MOP is intended to cripple Iran’s nuclear program at its foundations—literally and figuratively.
President Trump, addressing the nation after the strikes, claimed the facilities were “completely and totally obliterated,” a statement meant to project overwhelming U.S. firepower and resolve.
However, Iranian officials have pushed back against this. An advisor to Iran’s Parliament Speaker dismissed the attacks, stating that Fordow had already been evacuated and claiming, “Knowledge cannot be bombed.” Yet, the psychological impact of the strike—and the signal it sends to Iran and the wider region—is undeniable.
Why the MOP and Not a Nuclear Option?
While the US has the technological means to use low-yield nuclear weapons for such operations, the MOP offers a non-nuclear alternative with comparable penetrative force, minimizing diplomatic fallout while achieving strategic destruction.
Using the MOP allows Washington to walk the line between maximum force and controlled escalation, especially in a volatile theatre like the Middle East, where nuclear use would risk a far broader conflict and global condemnation.
What Next?
With the GBU-57 now in active use and Iran promising swift retaliation, the threshold for wider war has been crossed. Tehran has vowed that all US military and civilian assets in the region are now “legitimate targets.” The strike may also serve as a prelude to further U.S.-Israeli coordination aimed at either compelling Iran to capitulate—or paving the way for regime destabilization.
Diplomatically, the strike tests the silence of global actors, including Russia, China, and the European Union, and may reshape the non-proliferation regime centred on the NPT and the IAEA, both of which Tehran has accused of complicity through inaction.
Team BharatShakti
