Britain is to deploy troops, tanks and jets to Eastern Europe to deter Russian aggression.
In the biggest military build-up in Eastern Europe since the Cold War, an armoured force will be deployed to Estonia.
RAF planes are also being dispatched to patrol Romanian airspace for the first time.
The moves are designed to stop Moscow taking over or undermining its former Eastern European satellites as it has with Crimea and Ukraine.
The UK is sending 800 troops to Estonia as part of a Nato reaction to Russian aggression in Eastern Europe, with both sides increasing their military capability in eastern Europe in the biggest military build-up since the Cold War
In other developments:
Vladimir Putin upgraded the firepower of his Baltic Fleet with more ships and missiles;
40million Russians took part in four days of nuclear defence drills;
Spain cancelled plans to refuel Russian vessels heading for Syria.
Several Nato states, including Estonia, fear they could be next on President Putin’s hit list. And fellow members, including the UK, have a legal duty to defend them.
The alliance’s build-up will see 800 UK troops deployed to Estonia for six months from May. They will be relieved by soldiers from another Nato nation to keep up a continuous presence.
Sir Michael Fallon said the British mission would incorporate Challenger 2 tanks, Warrior vehicles and hand-held drones.