10 things to know about the US stealth bombers that dropped 13,600 kg bombs on Iran

An airman prepares a dummy 5000 lbs. 'bunker buster' for a demonstration of bomb loading on a mock B-2 during Bomber Media day at Whiteman Air Force Base 30 October, 2002 Missouri. (Image credit: AFP)

In a dramatic escalation of tensions, the United States recently confirmed using "bunker buster" bombs in strikes against three key Iranian nuclear sites. These specialised munitions, designed to penetrate hardened underground facilities, signify a significant shift in the conflict. As the world grapples with the implications, here are 10 essential things to understand about the formidable weapons deployed by the US military.

1. What are stealth bombers?
Built by American aerospace giant Northrop Grumman, the B-2 Spirit is better known as the Stealth bomber. This remarkable aircraft can slip past even the most advanced air defences to carry out pinpoint strikes on fortified targets, including deeply buried nuclear research facilities like those in Iran. Multiple B-2s were reported to have departed from their base in Missouri prior to the strikes.

2. Costs around $2.1 billion each
The B-2 is staggeringly expensive – each one costs around $2.1 billion, making it the priciest military aircraft ever built. But its hefty price tag comes with a massive reach: it can fly over 6,000 nautical miles without needing to refuel, allowing it to launch attacks directly from bases in the US.

3. What are bunker busters and GBU-57 massive ordnance penetrator (MOP)?
Bunker buster is a broad term for bombs engineered to penetrate deeply buried and fortified structures, such as command centres, weapons caches, or nuclear facilities, before detonating. They are distinct from conventional bombs due to their robust casings and delayed fuzing systems, which allow them to bore through earth or concrete. The US primarily used the GBU-57 MOP in the recent strikes on Iran. This behemoth is the largest non-nuclear bomb in the American arsenal, weighing approximately 13,600 kg and measuring over 6 meters (20.5 feet) in length.

4. Penetration power
The GBU-57 is designed for extreme penetration. While exact figures can vary depending on the material, it's designed to penetrate up to 200 feet underground before exploding, Al Jazeera reported. It is also reported to be capable of burrowing through up to 18 meters (59 feet) of reinforced concrete. The warhead is encased in a special high-performance steel alloy, which helps carry a large explosive payload while maintaining the penetrator case's integrity during impact, an Air Force fact sheet stated. This remarkable capability is crucial for reaching deeply buried targets like the Fordow facility. This remarkable capability is crucial for reaching deeply buried targets like the Fordow facility.

'Bunker busters' are designed for extreme penetration. (File photo: AFP)

5. How do they work?
Bunker busters employ a combination of immense weight, a hardened steel casing, and precision guidance. They are dropped from high altitudes, gaining significant kinetic energy. Upon impact, the robust casing allows them to tunnel through layers of earth or concrete. A delayed fuze then ensures the bomb explodes after reaching the target depth, maximising destructive force within the underground structure.

6. Targeted Iranian nuclear sites
President Donald Trump confirmed that the US struck three primary Iranian nuclear sites: Fordow, Natanz, and Esfahan. Fordow, being buried deep within a mountain, was a prime target for the bunker busters, with Trump stating that a "full payload of BOMBS" was dropped on it.

7. First combat use of GBU-57The recent strikes on Iran mark the first reported combat use of the GBU-57 Massive Ordnance Penetrator. This signifies a new level of military engagement and a demonstration of the US's capability to target deeply buried facilities.

8. Advanced precision guidance system
Beyond their sheer destructive power, these bombs are noted for their precision. The GBU-57 incorporates advanced guidance systems, combining Global Positioning System (GPS) and Inertial Navigation System (INS) technology. This ensures extreme accuracy, allowing the bomb to strike within metres of its intended target.

9. Strategic purpose: Neutralising hardened targets
The development and deployment of bunker buster bombs like the GBU-57 directly address the strategic challenge posed by highly fortified and deeply underground military and nuclear facilities. These structures are designed to withstand conventional airstrikes, making specialised penetrator munitions essential for their destruction. Their use underscores a strategic aim to degrade Iran's nuclear infrastructure, Reuters reported.

10. Other munitions also used 
While the GBU-57 was central to the attack on Fordow, it was not the sole munition employed. Reports indicate that approximately 30 Tomahawk cruise missiles were also fired at other Iranian nuclear sites, including Natanz and Esfahan. These missiles were reportedly launched from US submarines.