What are bunker busters: Everything to know about the $500M bombs

A 15-ton “bunker buster” bomb was likely needed to destroy the last untouched nuclear facility in Iran, and only the US had one.

Such a powerful weapon — the largest non-nuclear bomb in the US arsenal — was needed because the target, the Fordow fuel enrichment plant, is built some 300 feet inside a mountain near the city of Qom, two hours south of Tehran.

The heavyweight explosive is known as a GBU-57A/B Massive Ordnance Penetrator and was designed by Boeing for the United States Air Force.

Its huge weight means it can only be delivered with a B-2 Spirit stealth bomber — a jet that Israel’s air force does not possess.

“The United States controls the bomber and the bomb,” John Spencer, chair of urban warfare studies at the Modern War Institute at West Point military academy, recently told The Post.

The missile cost over $500 million for the US Army to develop, and was built to specifications that would allow it to penetrate deep enough into the Fordow plant to destroy the nuclear centrifuges in the complex, according to a 2013  Wall Street Journal report, which said at that time 20 of the bombs had been manufactured for the US military.

A different type of “bunker buster” bomb is the 5,000-pound GBU-37.

Read the latest on the US bombing of Iran’s nuclear facilities:

• US strikes Iran live updates: Trump to address the nation on ‘very successful attack’ on three nuclear sites
• US has bombed three nuclear sites in Iran, Trump announces: ‘Now is the time for peace’
• GOP leaders, Sen. John Fetterman commend Trump’s strikes on Iran: ‘The correct move’
• Trump’s Iran attack catches world off-guard after fakeouts with B-2 flights and ‘two weeks’ timeframe

“By weight and kinetic force, the GBU-57A/B Massive Ordnance Penetrator is designed to penetrate a certain amount of distance into the ground before it blows,” said Spencer.

“That’s why these bunker busters are called Penetrators. They penetrate the ground before they explode. The explosion is strategically delayed.”

Although the US has sold less powerful bunker buster weapons to Israel, it has declined to share the Massive Ordnance Penetrator with any of its allies.

“I’ve seen 500-pounders, and they’ll shake your teeth when they go off. It’s like an earthquake,” said Spencer. “This will be much more than that.”