US is firing 5,000lb 'penetrator' bombs on Iran - how do they work?

The new advanced GBU-75 5K penetrator bombs have been deployed to Iran (Picture: USAF)

US Central Command said the US military has fired 5,000lb penetrator bombs on missile sites along Iran’s coastline.

The munitions,named by a government official as GBU-72 Advanced 5k Penetrator bombs,were first released in 2021.

The US released them over Iran in hopes of reaching ‘hardened,deeply buried target challenges’ – namely,missile silos along the Strait of Hormuz.

The Air Force describes it as: ‘The weapon design and its projected effectiveness were developed using advanced modelling and simulation techniques and processes before the first warhead was forged.

‘This is a repeatable process for all future direct attack weapons. Lethality is expected to be substantially higher compared to similar legacy weapons like the GBU-28,according to James Culliton,GBU-72 program manager.’

The lethal weapons have only been used in combat a few times – so how do they work?

Deadly ‘bunker busters’ explode deep underground

The bombs are dropped by B-2 Spirit stealth bombers (Picture: Getty)

The GBU-72 Advanced 5k Penetrator bombs have been nicknamed ‘bunker busters’ for their capabilities.

The massive bombs are surrounded by steel,which allows the explosives to burrow deeply through the ground and concrete bunkers,exploding once they reach a certain depth.

Casting made of hardened ferro-cobalt alloy to survive impact,the warhead alone weighs 5,291 pounds and can enter through almost 200 feet of concrete.

The bomb used in Iran last summer was slightly different,however – the GBU-57 30,000-pound precision-guided bomb was used to penetrate the web of underground bunkers where Iran carried out its nuclear programme.

The US used GBU-57s to strike nuclear sites in Iran last summer (Picture: AP)

Iran’s state-run IRNA news agency confirmed the Fordow,Isfahan and Natanz nuclear sites had been attacked during the summer 2025 conflict.

B-2 bombers are only used by the US military,and they are the only aircraft capable of carrying and delivering the penetrator bomb.

The bombs were dropped by B-2 Spirit planes and guided to their targets by GPS systems,reaching supersonic speed before impact.

Each penetrator from the bombs used last summer weighed 30,000 pounds.

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