GBU-57 bunker buster: The U.S. super bomb that crippled Iran’s nuclear sites

'Grave violation': Iranian Foreign Minister Araghchi warns of everlasting consequences after US strikes nuclear facilities.

The U.S. strikes on Iran’s nuclear facilities in the wee hours of June 22 have brought back to the spotlight a rarely used but highly specialised class of weapons - bunker buster bombs, or ground penetration munitions.

These powerful bombs are designed to destroy deeply buried or fortified targets that are otherwise inaccessible to conventional ordnance.

What are bunker buster bombs?

Bunker busters are engineered to penetrate hardened structures such as underground bunkers, command centers, and nuclear facilities before detonating. These bombs rely on a combination of kinetic energy, hardened steel casings, and delayed fuses to burrow deep into the earth or reinforced concrete, often up to 30 meters of soil or 6 meters of concrete, before exploding.

Notably, the concept dates back to World War II, with Germany's Röchling shells among the earliest prototypes.

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The Massive Ordnance Penetrator: America’s ultimate bunker buster

Designed to hit deeply buried targets such as Iran's heavily fortified nuclear facilities, the GBU-57 can burrow through up to 200 feet of earth or rock before detonating.

Unlike traditional bombs or missiles, which typically explode on or just beneath the surface, the GBU-57 is built with a reinforced steel casing and a specialized fuse that withstands immense impact pressure.

“You need an explosive that's not going to immediately explode under that much shock and pressure,” according to Masao Dahlgren, a missile defense expert at the Center for Strategic and International Studies (CSIS) in Washington, cited in an AFP report.

At 6.6 meters long and weighing 30,000 pounds, the MOP is the largest conventional bomb in the U.S. arsenal. It was designed in the early 2000s, and Boeing received its first production order in 2009 for 20 units

It uses a specially hardened casing to survive extreme impact, along with a sophisticated fuse that withstands the shock until the bomb reaches its intended depth. The weapon was developed in the early 2000s, with Boeing receiving a production contract in 2009.

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Now, how is the GBU-57 deployed? Let's understand here.

Notably, only the U.S. B-2 Spirit stealth bomber is capable of carrying and deploying the GBU-57.

It is built with a flying wing design and advanced stealth technology, allowing it to evade radar and deliver heavy payloads anywhere in the world. Each aircraft can carry two MOPs per mission.

Thanks to their long-range capabilities and aerial refueling, B-2 bombers can conduct nonstop bombing runs from the U.S. to the Middle East.

“They’re able to fly all the way to the Middle East to do bombing runs. That’s been done before,” Masao Dahlgren, a fellow at the Center for Strategic and International Studies, has been cited in the AFP report last week.

Satellite imagery reportedly analysed by AFP and Planet Labs confirmed the presence of B-2s at Diego Garcia in early May. Their subsequent absence by mid-June raised speculation that they had been deployed for the Iran mission.

During the June 22 strikes on Iran’s Fordow, Natanz, and Isfahan nuclear facilities, sites known for being deeply buried and heavily fortified, B-2 bombers were dispatched from U.S. bases.

They reportedly operated either from Diego Garcia, a joint UK-U.S. base in the Indian Ocean, or directly from the continental U.S., using mid-air refueling.

President Donald Trump later described the strikes as a “spectacular military success,” declaring that Iran’s key nuclear enrichment facilities had been “completely and totally obliterated.”

What are the other types of bunker busters? Let's find out here:

The U.S. military, besides the GBU-57, uses other types of bunker busters as well.

These are:

GBU-28: Weighs about 5,000 pounds, uses laser guidance, and was first developed during the Gulf War using repurposed artillery barrels.
GBU-37: A GPS-guided variant effective in all weather conditions, designed for accurate targeting of buried facilities.

This undated US Air Force handout image obtained 28 April 2005, shows a GBU-28 "bunker buster", a 5,000lb (2268kg), unpowered, hard target laser-guided weapon, with a range of more than six miles (9.65km). (AFP file image)

All these bombs are equipped with advanced guidance systems (laser or GPS) to minimise collateral damage and enhance the precision of the strikes.

Nevertheless, there are some ethical and legal concerns

While bunker busters are not banned under international law, their use in civilian-dense areas raises serious humanitarian concerns. The Geneva Conventions prohibit indiscriminate attacks that could cause excessive civilian harm.

These concerns resurfaced last September after Iran accused Israel of using U.S.-supplied bunker busters in strikes on Hezbollah sites in Beirut, located under residential buildings.

Over the past two decades, the U.S. has supplied Israel with bunker buster bombs:

2005: 100 GBU-28 bombs.2014: Additional transfers amid rising tensions in the region.

2023: Over 1,000 bombs as part of a $6.5 billion military aid package.

Israel, however, does not possess the GBU-57 or the B-2 bomber, limiting its ability to strike ultra-hardened targets like Fordow.

Interestingly, this makes the U.S. strike on Iran’s facilities particularly significant in terms of military capability and geopolitical messaging.

The use of bunker busters by the U.S. signals a major escalation in Washington's involvement in the Iran-Israel conflict. By deploying a weapon that only it possesses, the White House has sent a clear warning to Tehran about the costs of continuing its nuclear ambitions.

At the same time, the operation raises the risk of broader regional instability and potential retaliatory strikes by Iran or its proxies.