NATO is launching its largest exercise since the Cold War, rehearsing how U.S. troops could reinforce European allies in countries bordering Russia and on the alliance’s eastern flank if a conflict were to flare up with a “near-peer” adversary.

Some 90,000 troops are due to join the Steadfast Defender 2024 drills that will run through May, the alliance’s top commander Chris Cavoli said on Thursday.

More than 50 ships from aircraft carriers to destroyers will take part, as well as more than 80 fighter jets, helicopters and drones and at least 1,100 combat vehicles including 133 tanks and 533 infantry fighting vehicles, NATO said.

Cavoli said the drills would rehearse NATO’s execution of its regional plans, the first defence plans the alliance has drawn up in decades, detailing how it would respond to a Russian attack.