What are US bunker-buster bombs that hit Iran's underground missile sites?

In a shift towards targeting underground military infrastructure, the United States (US) used its latest 5,000-pound bunker-buster bombs to strike Iranian missile sites near the strategically critical Strait of Hormuz, marking a significant escalation in the ongoing conflict.  According to reports, the bombs used in the overnight strikes could mark the first operational use of the Guided Bomb Unit‐72 (GBU‐72), also known as the Advanced 5K (A5K) Penetrator, although this has not been officially confirmed.  “Hours ago, US forces successfully employed multiple 5,000-pound deep penetrator munitions on hardened Iranian missile sites along Iran’s coastline near the Strait of Hormuz,” US Central Command (CENTCOM) posted on X confirming the strikes.   The command added that the targeted missiles “posed a risk to international shipping in the strait.” While the specific weapon was not named, the GBU-72 - the US’ latest 5,000-pound bunker-buster— is believed to be among the likely munitions used.  Admiral Brad Cooper, commander of US CENTCOM, said in a video statement that eliminating Iran's “naval threats” is one of the Operation's three military objectives.  “We're also zeroed in on dismantling Iran's decades-old threat to the free flow of commerce through the Strait of Hormuz,” Cooper said on Monday. “Through a combination of air, land, and maritime capabilities, we have successfully destroyed over 100 Iranian naval vessels, and we aren't done.” 

What is a bunker-buster bomb?

A bunker-buster is a specially designed bomb built to destroy targets buried deep underground or protected by reinforced concrete.  Unlike conventional bombs that explode on impact, bunker-busters penetrate the ground first. They use a hardened steel casing to drill through layers of soil, rock or concrete before detonating inside the structure.  The likely weapon used in these strikes, GBU-72, is part of a newer generation of bunker-busters. It weighs around 5,000 pounds (approx. 2200 kilograms) and is designed specifically to hit “hardened” or deeply buried targets that normal bombs cannot destroy. 

How does it work?

The bomb is typically dropped from fighter jets or bombers and guided using Global positioning-based systems.  Once it hits the target, its weight and reinforced casing allow it to go underground. After reaching a certain depth, it explodes, causing maximum damage within the bunker or facility rather than on the surface.  This makes it especially effective against hidden military infrastructure such as missile storage sites, underground launch pads and command centres.  The targets in Iran were not ordinary military bases, but underground missile facilities located near the Strait. These sites were reportedly being used to launch or store anti-ship cruise missiles, which could and have targeted commercial vessels and oil tankers moving through the region.  The usage of GBU-72 suggests that such weapons are used only when targets are heavily fortified, indicating that the US is now focusing on neutralising Iran’s core military infrastructure rather than just surface-level capabilities.