The US Air Force has the medicine for evil-regime deep bunkers. But it needs more

A USAF B-2 Stealth bomber. The 19 B-2s are the only aircraft which can currently carry the massive GBU-57 bunker busting munition
A USAF B-2 Stealth bomber. The 19 B-2s are the only aircraft which can currently carry the massive GBU-57 bunker busting munition - Cristobal Herrera-Ulashkevich/EPA_EFE/Shutterstock

Desperate to avoid US air attack in the event of a major war, America’s foes are digging in – literally. China, North Korea and Iran are all building more, and deeper, underground military facilities. And the Pentagon is scrambling to keep up – with new bunker-busting bombs.

The newest of these bombs made a surprise appearance over the Mojave Desert back in March. Photographer Ian Recchio snapped photos of a US Air Force Boeing B-1 bomber refuelling from a USAF KC-135 tanker. There was something unusual under the swing-wing B-1’s forward fuselage: a large bomb.

Aviation expert David Cenciotti was one of the first people to see Recchio’s photos. At first, Cenciotti thought the bomb might be a GBU-31, an unremarkable 2,000-pound satellite-guided bomb. But then he looked closer.

It wasn’t a GBU-31. It was a new munition: a rarely-seen 5,000-pound GBU-72 designed to penetrate dirt and rock before exploding. A bunker-buster.

A satellite image of Iran's Natanz nuclear site on April 14 2023. New underground facilities at the site may have put Iranian uranium enrichment centrifuges beyond the reach of current bunker buster weapons
A satellite image of Iran's Natanz nuclear site on April 14 2023. New underground facilities at the site may have put Iranian uranium enrichment centrifuges beyond the reach of current bunker buster weapons - Planet Labs/AP

The GBU-72 is special. With its high-tech fuse and extra-hard casing, the satellite-guided bunker-buster is both highly penetrative and relatively small. In other words, it combines the best qualities of the US Air Force’s existing bunker-busters: the 4,000-pound GBU-28 and the 27,000-pound GBU-57.

The GBU-28 is small and light enough to be carried by the US Air Force’s Boeing F-15E fighters, but it penetrates less than 200 feet of hard earth. The GBU-57 should penetrate deeper than 200 feet, but it’s so big and heavy that only two USAF warplane types can carry it: the current B-2 stealth bomber and the future B-21 stealth bomber, both built by Northrop Grumman.

We don’t know how deep a GBU-72 could dig before it explodes. But “lethality is expected to be substantially higher compared to similar legacy weapons like the GBU-28,” the US Air Force stated, citing James Culliton, the GBU-72 program manager.

The GBU-72 might not be as powerful as the massive GBU-57, but it’s also not limited to carriage by the tiny fleet of just 19 B-2s – or the somewhat less tiny future fleet of a hundred or so B-21s. The US Air Force first tested the GBU-57 on an F-15E in 2021. The Air Force has around 200 F-15Es, and is replacing half of them with newer F-15EXs.

The service also has 44 B-1s that could carry the GBU-57. And if the B-1s are compatible with the bombs, there’s no reason the US Air Force’s 76 Boeing B-52 bombers – not to mention the B-2s and future B-21s – shouldn’t also be compatible.

All that is to say, many hundreds of American warplanes could carry GBU-72s. During a major war, these planes could go after shallower buried targets while the smaller force of bombers hauling GBU-57s goes after deeper buried targets.

The range of potential targets is daunting. Iran has dug underground bunker complexes to house rocket launchers, fighter squadrons and critical parts of its growing nuclear-weapons enterprise. A new underground nuclear complex is apparently more than 300 feet underground.

North Korea has also buried parts of its own nuclear weapons complex – and also maintains vast underground bases for artillery, rockets, fighter jets and even helicopters, often dug into the sides of mountains. It’s not for no reason US and South Korean troops routinely train for tunnel warfare.

China is digging in, too. The People’s Liberation Army “maintains a robust and technologically advanced underground facility program to conceal and protect all aspects of its military forces,” the Pentagon explained in the 2023 edition of its annual report on the Chinese military.

China’s underground bases house headquarters, ammunition stockpiles, nuclear warheads, supply depots and air, ground and naval forces. China has thousands of underground facilities “and constructs more each year,” according to the Pentagon report.

In a major war with any of these foes – Iran, North Korea or China – a token force of GBU-57-armed B-2s might be too small to dent the underground infrastructure. And the larger force of fighters carrying GBU-28s might be powerless to penetrate the deeper targets.

The GBU-72 should address this dilemma – by arming hundreds of American warplanes with deeper-digging bunker-busters.

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