NATO has announced its biggest call-up in decades as 90,000 troops prepare to begin World War 3 drills in a matter of days.
Among that number will be 20,000 British troops as the alliance plans to test allies on their ability to engage in conflict with an adversary as capable as Russia.
Steadfast Defender will begin next week and run to late May, involving units from all 31 NATO member countries plus candidate-member Sweden.
NATO's Supreme Allied Commander Europe, US General Christopher Cavoli, told journalists in Brussels of the groundbreaking news after a two-day meeting of national defence chiefs.
"The Alliance will demonstrate its ability to reinforce the Euro-Atlantic area by a transatlantic movement of forces from North America," Cavoli said.
The wargames are meant as a fresh show of strength from NATO and its commitment to defend all allied nations from attack.
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The UK's 20,000 troops will be sent alongside the Royal Navy's two new aircraft carriers and eight warships.
The RAF's F-35 lightning attack aircraft will also be present and tested with imitated conflict scenarios.
Defence Secretary Grant Shapps announced the deployment of all three Armed Forces to the 31-nation drill on Monday.
It comes as the prospects of World War 3 continue to grow with ongoing conflict around the world.
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But NATO's exercise is primarily preparing for potential aggression from Russia.
Earlier this week, a leaked military report revealed what could be Vladimir Putin's step-by-step plan to bring the West to the brink of World War 3 - and it starts in weeks.
The secret docs detail the despot's possible "path to conflict" which reaches its climax in the summer of 2025 on "Day X" when half a million Nato and Russian soldiers will face each other.
The UK continues to support Ukraine in their battle against Russia, however, with ministers announcing a further £2.5billion support package earlier this week.
But military strikes alongside the US against Iran-backed Houthi rebels in Yemen have also raised concerns of all-out warfare.
Foreign Secretary Lord Cameron told Sky News it was “hard to think of a time when there has been so much danger and insecurity”.
Germany will also send 12,000 soldiers to Steadfast Defender, according to national newspaper , along with 3,000 vehicles and 30 aircraft.
Citing the German Press Agency, Bild said the exercise will simulate a Russian attack on NATO territory, a scenario which would trigger Article 5.
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The article states that if any NATO country is attacked, all other alliance countries will mobilise to defend it.
The largest NATO exercise since the cold war took place in 2018 as 51,000 troops participated in 'Trident Juncture 2018' in Norway.