A soldier careens into the briefing tent of Cross Functional Team (CFT) Taiwan, barely able to catch his breath.

“Attention on the floor!” he shouts. “Sorry to barge in, sir, but you’ll want to hear this.”

Chinese ships have begun to cross the Taiwan Strait “with full intention to invade”.

Chaos breaks out in the command centre, where specialists had been outlining recent operations. Sirens blare, soldiers pick up rucksacks, plastic chairs are pushed aside.

Over the tree-line, hostile drones whirr into view. As troops hustle a visiting congressional delegation to an evacuation point, they swoop overhead and drop munitions.

Ear-splitting explosions send plumes of smoke into the air. People fall by the side of the road, screaming.

So begins the long-feared war between the world’s two largest militaries – or at least, a drill simulating the event at the 25th capability exercise of the US Special Forces at Fort Bragg army base.

A hint of slapstick lingers in the air. Called upon to help the wounded, visitors fiddle with their lanyards, while fake blood soaks the clothes of gurgling actors.

The scenario, however, is head-poundingly serious.

Xi Jinping, the Chinese president, has ordered his military to be ready to “reunify” the self-governing island of Taiwan with the mainland by 2027.

An extraordinary build-up is under way. The People’s Liberation Army (PLA) now boasts one million troops more than the US, as well as the world’s largest navy, vast supplies of ground-based long-range missiles and a galloping nuclear arsenal set to hit 1,000 warheads by 2030.