'Cold War' cat-and-mouse’ games return under the sea
NATO fears Russia is targeting vital communication cables
NATO fears Vladimir Putin is prepared to cause financial chaos by attacking undersea cables between the US and the Europe and are going to extraordinary lengths to track Russian submarines.
US and UK military sources this weekend said that Russian submarine activity in the North Atlantic has reached a 25-year high and there has been a return to "Cold War cat-and-mouse games" under the sea.
Amid mounting tensions with the Kremlin, the allies are using a remarkable array of modern technology and military equipment to make sure they know exactly where the submarines are as they move around the region.
Satellites spot when the submarines leave naval bases and intercept communications, while planes fly over the sea scanning a 100-square-kilometre radius.
Helicopters dangle sonar buoys in the water to detect submarine movement, while warships drag pipes more than 800m-long rigged with underwater microphones.
NATO submarines with listening devices are able to follow the Russian submarines, while fixed listening devices placed on the seabed alert officials when they pass.
Western military figures liaise when a Russian submarine is being followed, with the Norwegians and other NATO countries also often being involved, notably France.
One fear is that Mr Putin could attempt to interfere with undersea communication cables that carry data on which stock markets in both the US and Europe are reliant.
"The largest exchange of data between America and Europe is via undersea cables," said one well-placed source. "Putin has the means and the capability to disrupt that if he wished. It is not stretching reality to paint a scenario where he would."
A US navy official said there had been a "return of great power competition" and that America has its "laser focused on increasing war-fighting readiness" to counter foes.
In the wake of the Soviet Union's collapse in 1991 much of the country's navy - the pride of the nation since Peter the Great - was sold off or junked. However under Mr Putin's leadership there has been a concerted effort to build up the Russian navy again, with a particular focus on submarines.
In recent years, as Russia annexed Crimea where its Black Sea fleet was based, stoked civil war in Ukraine and meddled in a US election, there has also been an increase in Russian activity under the North Atlantic.
Currently, at most times of the year there is at least one Russian submarine in the region or heading towards it. The surge in activity has sent NATO scrambling to re-engage. In March, the UK deployed a submarine under the Arctic for the first time in a decade.
Earlier this year America re-established its Second Fleet, which is responsible for patrolling the North Atlantic and had been inactive since 2011.
NATO is also creating a new joint forces command for the region based in Norfolk, Virginia.