LONDON—The U.K. called in assistance to help hunt for a foreign submarine off the west coast of Scotland starting in late November.

Maritime patrol aircraft (MPAs) from France, Canada and the U.S. conducted patrols in conjunction with British surface warships in the search for the submarine in late November and the first week of December, operating out of RAF Lossiemouth in northern Scotland.

The incident began when a periscope was sighted in waters where U.K. and other submarines would normally surface as they head into or out of the Royal Navy’s submarine base at Faslane, home of the U.K.’s ballistic missile submarines.

At the height of the operation, aircraft involved in the hunt included two U.S. Navy P-3 Orions, a single CP-140 Aurora from the Royal Canadian Air Force and a Dassault Atlantique 2 of the French navy. Also involved was one of the U.K.’s Raytheon Sentinel radar-reconnaissance aircraft.

The U.K. defense ministry and the participating air arms have not confirmed they were hunting for a submarine. But a U.K. defense ministry spokesman told Aviation Week that Britain had “requested assistance from allied forces for basing of maritime patrol aircraft at RAF Lossiemouth for a limited period. 

The aircraft are conducting Maritime Patrol activity with the Royal Navy; we do not discuss the detail of maritime operations.”

A spokesman for the Royal Canadian Air Force said: “Following a request for assistance from the United Kingdom, the Canadian Armed Forces deployed one CP-140 Aurora Aircraft to RAF Lossiemouth for a limited time.”

Maritime patrol aircraft are occasionally deployed to Scotland, mainly for NATO’s Joint Warrior exercise. Such exercises are usually announced in advance, but November’s deployment was unexpected, with the aircraft and supporting airlifters arriving around Nov. 26. The deployment appeared to end last last week.

The incident comes more than a month after Swedish authorities halted a search for a foreign submarine operating in its territorial waters in the Stockholm archipelago. While the Swedish search was unsuccessful, defense officials said there was no doubt that the country’s waters had been violated by a foreign power.

It is not clear whether the submarine being hunted by the U.K. and other Western nations had entered U.K. territorial waters, or if the maritime patrol aircraft successfully located the sub.

The Sentinel may have been using its radar to try to spot periscope-sized objects on the surface and then cue MPAs onto the target.

On Nov. 28, the U.K. reported it was tracking four Russian warships passing through the Strait of Dover and into the English Channel heading out into the Atlantic. The surface ships included a Ropucha-class landing ship and an Udaloy-class destroyer. These were shadowed by HMS Tyne, a Royal Navy offshore patrol vessel.

The U.K. retired its own fixed-wing maritime patrol capability provided by the Nimrod in 2010, and has been limited to the use of ships and helicopters for the anti-submarine mission.