It is the terrible moment the world has long feared. An army of Russian tanks and troops rolls across the border of a Baltic state in an act of naked aggression by Vladimir Putin’s regime.

Britain, the US and other Western nations are obliged by treaty to come to the defence of a fellow Nato member.

Within hours, the escalating conflict is poised on the precipice of a nuclear conflict that will claim millions of lives.

Our dramatic pictures show the incredibly life-like exercise on Salisbury Plain, intended to simulate President Putin’s forces invading Estonia, according to Army sources

This is the chilling scenario simulated by the British Army in one of the most realistic war games ever staged, revealed in these exclusive photographs obtained by The Mail on Sunday.

Our dramatic pictures show the incredibly life-like exercise on Salisbury Plain, intended to simulate President Putin’s forces invading Estonia, according to Army sources.

Taking part were troops due to be deployed early next year to shore up Nato forces in the Baltic states.

Every detail was as close as possible to those British soldiers will experience if Putin goes into Estonia.

Taking part were troops due to be deployed early next year to shore up Nato forces in the Baltic states

This demonstration on Salisbury Plain is exactly what I expect the Army to be doing, writes General Sir Richard Shirreff, and obviously they’ve thought it through

The enemy wore distinctive blue uniforms resembling Russian military police outfits and were equipped with AK-74 semi-automatic assault rifles issued to Russian troops.

Every detail was as close as possible to those British soldiers will experience if Putin goes into Estonia

The ‘Russians’ launched a tank assault using the T-72, a model recently upgraded by the Kremlin at £20 million per tank.

As well as the Polish-built T-72 there were three other Soviet-design tanks, supplied by a private collector and the Tank Museum.

UK forces responded with missile strikes from Apache helicopter gunships and bursts of fire from Warrior armoured fighting vehicles.

Challenger tanks patrolled the battlefield and RAF Tornados performed mock bombing runs.

The Ministry of Defence confirmed some of the troops are expected to deploy to Estonia.

The 400 UK soldiers will be within range of thousands of Russian troops and nuclear-capable missiles at Kaliningrad on the Baltic Sea.

Due to Army cuts, the MoD used a recruitment agency to find civilians to play enemy troops for the exercise. Gurkhas also became ‘enemies’.

A defence source said: ‘The idea was to simulate elements of Russia’s invasion of eastern Ukraine in 2014, which included a rapid seizure of territory which led to the annexing of Crimea.’

The UK troops will be part of the biggest Nato deployment in the Baltic region since the Cold War. It comes after Russian military manoeuvres in areas bordering Estonia, Latvia and Lithuania.

Some fear that Putin wants to test the West after US President-elect Donald Trump questioned the Nato alliance.

Just a war game? No, the threat is terrifyingly real

By General Sir Richard Shirreff

Ex-Nato Deputy Supreme Commander Europe - and author of 'War with Russia'

The defence of Britain starts these days not at the White Cliffs of Dover, but in the forests of Estonia, Latvia and Lithuania – to whose defence we are committed under Article 5 of the Washington Treaty of 1949 which created Nato.

This demonstration on Salisbury Plain is exactly what I expect the Army to be doing, and obviously they’ve thought it through.

It also sends exactly the right message about the importance of an effective deterrent

It also sends exactly the right message about the importance of an effective deterrent.

Estonia, Lithuania and Latvia are no backwater. Rather they are the new front line in a very dangerous world. The spotlight is on the Baltic states now as it was on Berlin and the Hanover Plain during the Cold War.

The Baltic is the most dangerous place from a British perspective, one of the reasons being that these states have such significant Russian-speaking populations – about 20 per cent in Estonia and 27 per cent in Latvia.

Estonia, Lithuania and Latvia are no backwater. Rather they are the new front line in a very dangerous world

And we only need to go back to the Crimea and how President Putin claimed that Russia should look after the interests of all Russians, wherever they are, to realise how he might seek to justify any encroachment into the Baltic territories.

Any notion that he has a right to interfere with his neighbours on the basis that their populations include Russian speakers – in a process that has been called ‘linguistic imperialism’ – is ridiculous and highly dangerous.

In Crimea, President Putin also went to great lengths to claim that his invasion was a civil war. He may do so again in the Baltic.

He may also seek to manipulate the Russian minorities in these countries using propaganda, cyber-warfare and other types of information warfare.

I have no doubt that what you’re seeing on Salisbury Plain is a response to a very serious conventional warfare threat, because, don’t forget, the Russians by their own admission have formed three divisions in their Western Military District, which is right on the doorstep of the Baltic states.

That is a really significant force, while Putin also continues to call snap exercises with immediate call-ups of as many as 40,000 troops at a time to demonstrate their readiness for war.