NATO is scrambling to find up to two Russian cruise-missile submarines believed to be shadowing French and US aircraft carriers operating off the coast of Syria.

The Russian Oscar-II submarines were built during the Cold War specifically to overwhelm the defences of US nuclear-powered aircraft carriers with swarms of missiles.

Russia has in recent years been steadily refurbishing and upgrading its fleet. Now it is believed two of these submarines are active in the eastern Mediterranean.

Атомный подводный ракетный крейсер «Томск» #ТОФ стал лучшим в #ВМФ России в стрельбе крылатыми ракетами в 2016 годуhttps://t.co/9B3r9MAlwu pic.twitter.com/fODQWioSdE — Минобороны России (@mod_russia) December 13, 2016

855 now RTB Sigonella after what looks like a successful task...? pic.twitter.com/Nbf4tgH7uI — Mil Radar (@MIL_Radar) December 12, 2016

The Aviatonist aviation blog reports military sources saying NATO anti-submarine forces are now attempting to locate and track these deadly submarines.

Of particular concern is the safety of the USS Eisenhower and the French Charles de Gaulle.

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Both aircraft carriers have been launching air strikes against Islamic State forces from waters off the coast of Syria.

Russia’s only aircraft carrier, the accident-prone Admiral Kuznetsov, and its escort of warships are also in the same area.

But NATO’s ability to locate such submarines — once its staple trade — is now in doubt.

Since the collapse of the Soviet Union, the United States — and in particular the United Kingdom — have allowed their submarine hunting abilities to wane.

Britain no longer has any sub-hunting aircraft, and its few remaining anti-submarine frigates are rapidly approaching the end of their useful lives.

In recent years the British government has repeatedly had to appeal to its European and American allies for the loan of aircraft and ships to tracking down Russian spy submarines believed to have been lurking of the coast of Scotland.

Thank you French aircraft carrier Charles de Gaulle for your contribution in support of #NATO Operation Sea Guardian. @MarineNationale pic.twitter.com/ZyMhRwzS1y — NATO MaritimeCommand (@NATO_MARCOM) December 13, 2016

The US is similarly having to cope with outmoded technology and techniques, though its new P-8 Poseidon submarine hunting version of the 737-800 airliner is taking part in this operation.

The 1980s vintage Russian Oscar class submarines are among the largest ever built.

At 154m long and 18m wide, they were designed to carry 24 nuclear-capable, high speed cruiser missiles. They are also fitted with six torpedo tubes, each also capable of launching missiles.

The presence of the submarines has little bearing on the Syrian civil war. Their missiles are not suited for attacking land-based targets.

It’s a similar story for the Russian Su-33 air superiority fighters now based in Syria. Neither Syrian rebels nor Islamic State operate aircraft.