Tense moments unfolded as a Royal Navy helicopter from Cornwall was at the forefront of an operation to monitor a Russian submarine cruising through British waters.
The vessel was tracked during its passage through the English Channel in a carefully coordinated three-day mission alongside NATO partners this month.
According to the Navy, the UK has witnessed a 30% rise in Russian ships posing threats to British waters over the last two years.
A specialist Merlin helicopter from Royal Naval Air Station Culdrose in Cornwall and RFA tanker Tidesurge kept close watch on the Russian Kilo-class submarine Krasnodar and its accompanying tug boat Altay as they travelled westwards from the North Sea, through the Strait of Dover and into the English Channel.
The Merlin helicopter, from 814 Naval Air Squadron at the base near Helston, stayed aboard RFA Tidesurge for the duration of the mission.
The Royal Navy stated: "Expert aircrew were prepared to pivot to anti-submarine operations if Krasnodar had dived below the surface."
The Russian submarine remained on the surface whilst traversing the Channel, despite turbulent weather conditions battering the UK.
Commanding officer of RFA Tidesurge, Captain James Allen, remarked: "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, said: "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 maintained surveillance of the Krasnodar and Altay until the Russian vessels approached the northwest coast of France, close to Ushant island, where monitoring duties were transferred to a NATO partner nation.