Stephen Chen in Beijing

Published: 10:00pm, 19 Jul 2025

Precision-guided bunker busters fly slowly but carry massive warheads wrapped in thick armour. Small nations without air power watch helplessly as bombs fall.

When US B-2 stealth bombers struck Iran’s nuclear sites with GBU-57 MOP (Massive Ordnance Penetrator) bunker busters on June 22, there was reportedly little resistance.

Chinese researchers have offered a countermeasure: strike the weak flank. Although the bomb’s nose armour is thick, its steel sides are thin and measure just a few centimetres, meaning one or two anti-aircraft shells could crack it open.

Low-cost anti-aircraft guns can be deployed around key sites. But the guns must survive, radar must track and electronic warfare must be countered.

Instead of China’s own weapon, the computer simulation used Swiss Oerlikon GDF guns which are widely fielded in the Middle East, including Iran.

The GDF fires 36 shells in two seconds. At 1,200 metres (0.7 miles), the kill probability hits 42 per cent.

The team led by Cui Xingyi, a researcher with Chinese weapons giant Norinco’s Northwest Institute of Mechanical and Electrical Engineering, published the method in the Journal of Gun Launch and Control, China’s top arms journal, on April 14.

Smart US bunker busters can be stopped by low-cost anti-aircraft guns. Photo: Northwest Institute of Mechanical & Electrical Engineering

Here’s how it works.

The bomb’s egg-shaped nose deflects frontal hits and only side strikes break through. Impact angles must stay under 68 degrees. Beyond that, shells glance off, according to Cui and his colleagues.

Beyond 1,500 metres (4,900 feet), penetration fails. Within 1,200 metres, the inert explosives inside the bomb can be ignited by heat and shrapnel.

The science is simple and based on calculations using World War II armour-piercing formulas.

But there is a trick: guns must pre-aim to a point in the smart bomb’s flight trajectory. The closer the point is, the better, as then the barrels stay put with minimum adjustment. Researchers call it “sniper fire control” tactics.

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“This sniper-style interception has several advantages,” Cui’s team wrote.

It lowers servo system demands and eliminates iterative calculations, slashing the response time to 1 millisecond.

“It is engineer-ready with current tech,” they added.

But combat is cruel. Air powers can use mass raids to clean up the guns before sending in the bombers. A smart bomb’s final manoeuvres can spoil trajectory prediction and the 1,200m window lasts for the blink of an eye.

Meanwhile, a Beijing-based physicist not involved in the study, noted: “What works in China may not work elsewhere.”

Stephen Chen

Stephen Chen is the SCMP's science news editor. He investigates major research projects in China, a new power house of scientific and technological innovation