The British government acknowledged today that a submarine periscope had been sighted in waters near a main U.K. base, touching off a massive NATO hunt in November.

The government also said that it had requested help from other nations in its search for the submarine off Scotland shores in November.

Sweden expands hunt for suspected Russian submarine.

Russia tests super-quiet submarine.

A pair of U.S. Navy P-3 Orions, as well as Canadian and French planes and two British warships, scoured the waters for days when the periscope was seen in November.

Britain reportedly got rid of similar sea-searching aircraft during defense cuts.

Russia has been flexing its military muscle recently, in Ukraine and throughout Europe.

Russia has been frequently flying bombing runs near NATO airspace. And at sea, Russian warships have conducted surprise exercises in the English Channel in November.

In October, the Swedish military said that a photograph and advanced sonar data had seemed to show a foreign submarine in the waters off Stockholm.

Russia has denied any involvement.

The Swedes hunted for the submarine for a month. All ships were ordered to leave a cluster of islands where the vessel had been possibly spotted. A no-fly zone was also put into effect over the area.

No trace of a submarine was found and the search was called off.