NATO is preparing its biggest live joint command exercise since the cold war next year, assembling more than 40,000 troops to practice how the alliance would attempt to repel Russian aggression against one of its members, The Financial Times said, Report informs.

The Steadfast Defender exercise comes as part of NATO’s rapid push to transform from crisis response to a war-fighting alliance, prompted by the invasion of Ukraine.

It will start in spring next year and is expected to involve between 500 and 700 air combat missions, more than 50 ships, and about 41,000 troops, NATO officials said. It is designed to model potential maneuvers against an enemy modeled on a coalition led by Russia, named Occasus for the purposes of the drill.

The exercise is also a first in terms of technical capability, using real world geographical data to create more realistic scenarios for troops.