At least a dozen specialist NATO warplanes have been launched to search for a Russian submarine suspected of threatening an American aircraft carrier. Photo: Getty Images

It is believed the aircraft completed 27 sorties in almost 48 hours since Sunday evening. It came as the US Navy's USS Gerald R Ford - the world's biggest aircraft carrier - and her strike group reportedly carried out training drills with the Norwegian Navy in the North Sea. The UK Ministry of Defence (MoD) confirmed sorties by the RAF was not an exercise.

A defence source said the mission was a "highly unusual surge", according to The Sun.

Former Royal Navy commander Tom Sharpe told the newspaper: "It looks like they have found a Russian submarine and they are hammering it.

"It is telling Russia: 'We see you.'"

It is believed the RAF made eight P-8A Poseidon flights from RAF Lossiemouth over the waters.

The UK has nine of the aircraft which specialise in anti-submarine warfare and maritime surveillance, equipped with sonobuoys for submarine detection and torpedoes.

America used a base in Iceland for the suspected submarine search, while at least two Poseidons were deployed from Sicily, The Sun reports. Norway also dispatched three Poseidons from a base inside the Arctic Circle.

The aircraft, which are based on the Boeing 737-800 airliner, reportedly turned off their transponders as they approached the search area to conceal their location to other pilots.

However, data from flight tracking websites showed an RAF Poseidon spent hours circling over an area of the Norwegian Sea.

An MoD spokesperson earlier told the Express: "The UK's P-8 Poseidon aircraft work continuously on operations, protecting national interests and keeping the UK and our allies safe.

"For security reasons we will not comment on operational details."