A Russian vessel passing through the English Channel over Christmas prompted a Royal Navy patrol ship to be dispatched to shadow it.
The HMS Tyne sailed out to keep an eye on the Smolnyy Perekov on Christmas Eve as it almost entered UK territorial waters.
The ship, based in Portsmouth, remained at sea on Christmas Day to monitor the Russian vessel, the Royal Navy said in a statement.
It was due to return to Portsmouth on Boxing Day.
More than 3,500 Royal Navy, Royal Fleet Auxiliary, Royal Marines and Fleet Air Arm personnel were either on duty or on short notice to respond to events at home and abroad this Christmas.
HMS Tyne’s Commanding Officer Commander Jon Browett said: “Leaving our families at this time of year is especially difficult, but national security doesn’t stop for Christmas, and as one of the duty units over the festive period we had bags packed and were ready to go."
He added some members of the ship’s company had to return at short notice, but that the armed forces were committed to keeping the UK safe at all times.
“Our families understand our role and undoubtedly make a tangible contribution to national security through their continued support.”
The Russian vessel was a Smolnyy-class ship built in the 1970s and used as a training ship for 30 crew and 300 cadets.
It usually carries a basic armament for self-defence and patrol duties. There are two Smolnyy Perekov ships attached to the Russian Baltic fleet.
Defence Secretary Ben Wallace said: “I am grateful for the efforts of the crew of HMS Tyne, who have sailed on Christmas Eve, helping to safeguard our seas.
“This is yet another clear example of the tireless efforts of our armed forces, as they continue their tireless efforts to defend out country and our interests across the world.”
Additional reporting by agencies
