Deep Dive The GBU-57 “Bunker Buster”: America’s Go-To Weapon for Targeting Iran’s Nuclear Facilities

In modern warfare, there are few weapons as intimidating — or as secretive — as the GBU-57A/B Massive Ordnance Penetrator. When the U.S. reportedly struck three of Iran’s nuclear facilities in Natanz, Fordow, and Isfahan during a late-night operation, many defense analysts immediately speculated about one key piece of the puzzle: what exactly did Washington use to get past the deeply buried defenses surrounding these sites? The answer appears to be a weapon so powerful that only nuclear arms could surpass it — but with a far more targeted purpose.

The GBU-57 is the largest conventional bunker-busting bomb ever developed, weighing in at more than 30,000 pounds (13.5 metric tons) and stretching nearly 20 feet in length. It was designed in the early 2000s after intelligence revealed that existing munitions simply couldn’t penetrate hardened underground targets. Containing almost 5,000 pounds (2.5 tons) of explosive material, the GBU-57 was built specifically to strike fortified enemy bunkers, deeply buried command centers, and high-value military infrastructure protected beneath layers of soil, stone, and reinforced concrete.

Designed for Deep Impact: What the GBU-57 Can Do​

There’s still a lot we don’t know about the full capabilities of the GBU-57, and that’s by design. Official data on penetration depth varies depending on source and context, but common estimates suggest that the bomb can reach up to 200 feet (60 meters) underground — though this figure generally applies to less dense soils. Against reinforced concrete, that number drops significantly; some analysts estimate around 60 feet (19 meters) of penetration in hardened structures, which still places it far beyond the reach of most other conventional bombs.

One particularly challenging target is Iran’s nuclear facility at Fordow, which is believed to be located beneath a mountain of granite. Western defense analysts suggest that it would take at least five GBU-57 bombs, each hitting with surgical accuracy, to fully neutralize a site like this. That’s no small feat. The bomb’s massive size and weight make delivery extremely complex, and precision is absolutely critical — a challenge compounded by the bomb’s speed and the lack of margin for error when striking underground fortifications.

While the use of the GBU-57 in Iran represents a potentially historic first, it's also what makes independent verification difficult. As of now, there are no publicly available images or video footage confirming the effects of the weapon in this particular strike, leaving much of its real-world impact open to speculation.

A Job Only America’s Stealth Bombers Can Handle​

Transporting and deploying a weapon like the GBU-57 requires serious airpower, and that’s where the U.S. Air Force’s B-2 Spirit stealth bomber comes in. Due to its size and weight, the bomb can only be delivered by select platforms — and the B-2 is the most viable and combat-tested aircraft capable of executing such a mission. The stealth bomber is one of the most expensive aircraft in the world and has seen action in Yugoslavia, Iraq, Afghanistan, and Libya. Notably, Israel — while widely considered a major regional power — does not possess B-2 bombers, making it highly unlikely that it could have carried out such strikes independently.

In the near future, the GBU-57 is expected to be integrated into the next-generation B-21 Raider, which is currently undergoing flight testing and is not yet operational. For now, the responsibility lies with the elite 509th Bomb Wing at Whiteman Air Force Base in Missouri, the only unit equipped to carry out missions involving the GBU-57.

Flying a B-2 from Missouri to Iranian airspace is no small journey — the round trip can take roughly 30 hours, making aerial refueling absolutely essential. Interestingly, one week prior to the reported strikes, more than 30 U.S. tanker aircraft (KC-135s and KC-46s) were redeployed to Europe under the guise of NATO exercises. While the Pentagon cited joint training missions, military observers noted a striking detail: many of the tankers involved were over 50 years old, hardly the kind of assets you’d move unless there was a more serious reason beneath the surface.

The Unknown Effectiveness — And Strategic Message​

This marked the first confirmed combat use of the GBU-57, and with it, a powerful message was likely sent: the United States still maintains a unique set of military capabilities that no other country — including its allies — can fully replicate. If the goal of the strike was to degrade Iran’s nuclear infrastructure without escalating into all-out war, then using a weapon like the GBU-57 allows Washington to thread the needle — delivering forceful impact while remaining (technically) within the realm of conventional warfare.

And yet, until the dust settles — both literally and politically — we may not know exactly how effective the strike was. Iran has remained quiet, and no visual evidence has emerged. But one thing is clear: when it comes to targeting the world's most heavily protected sites, this is the weapon America brings to the table — a near-nuclear punch delivered without crossing the nuclear threshold.