Dramatic scenes played out as a Royal Navy helicopter based in Cornwall led operations to track a Russian submarine passing through British waters.
The vessel was monitored throughout its journey across the English Channel during a meticulously planned three-day operation alongside NATO allies this month.
The Navy reports that Russian ships threatening British waters have increased by 30% over the past two years.
A specialist Merlin helicopter from Royal Naval Air Station Culdrose in Cornwall, together with RFA tanker Tidesurge, maintained close surveillance of the Russian Kilo-class submarine Krasnodar and its support vessel, tug boat Altay, as they moved westwards from the North Sea, through the Strait of Dover and into the English Channel.
The Merlin helicopter, operated by 814 Naval Air Squadron stationed at the base near Helston, remained deployed aboard RFA Tidesurge throughout the operation, reports Cornwall Live.
The Royal Navy stated: "Expert aircrew were prepared to pivot to anti-submarine operations if Krasnodar had dived below the surface."
Despite rough weather conditions affecting the UK, the Russian submarine stayed above water whilst navigating the Channel.
Captain James Allen, commanding officer of RFA Tidesurge, commented: "There is nothing like a Russian submarine to focus the mind for any mariner.
"Our tasking over the course of three days involved the teamwork and professionalism of all RFA Tidesurge ship's company, embarked 814 Naval Air Squadron Atlantic Flight and interoperability with near regional NATO allies.
"We worked together as a show of presence and deterrence as we transited from the North Sea to the English Channel."
Lieutenant Commander David Emery, flight commander of 814 Naval Air Squadron's Atlantic Flight at Culdrose, stated: "Maintaining an overt presence and continued over watch of Russian vessels in UK waters is vital for national security.
"The flexibility and professionalism of the crew of RFA Tidesurge allows us to project our helicopter wherever, day or night, in the maritime environment."
The Royal Navy kept a close eye on the Krasnodar and Altay until the Russian ships neared the northwest coast of France, close to Ushant island, where surveillance duties were handed over to a NATO partner nation.