NATO and even some non-NATO European forces on Monday began a series of large military exercises across Northern Europe as part of an expanded annual event. Ten NATO countries plus Sweden will take part in a two-week exercise aimed at detecting and hunting submarines in the North Sea close to Norway, while Estonia will host the biggest military exercise in its history as ground forces from nine allied countries practice battle operations.

While the exercises are taking place at a time of renewed Russian hostility, officers involved in the annual submarine exercise, known as Dynamic Mongoose, have said this year’s expanded edition is not aimed at any particular country.

“Obviously we’re aware of the incidents that have happened in some of our partner nations’ waters,” said Rear Adm. Brad Williamson, who commands the Standing NATO Maritime Group 2 ships participating in the exercise. "Russia has a right to be at sea, just as we do, but the incidents we have seen are not in line with international regulations... and that's been the cause of concern."

Despite not being part of NATO, neutral Sweden’s inclusion in the submarine exercise comes six months after it launched a large military operation when eyewitness reports suggested a Russian submarine was operating in the archipelago off Stockholm’s Baltic coast. Sweden's neighbor Finland dropped depth charges on indications that a Russian submarine had infiltrated Finnish territorial waters off the coast of the capital Helsinki. Neither country has publicly blamed Russia, although speculation has pointed to Moscow's involvement.

NATO has increased its operations around Europe and Eastern Europe over the past year, since Russia annexed Crimea in March 2014 and began intervening in the East Ukraine war the following month, an involvement that Moscow however denies.   

The exercise in Norway will involve submarines from Germany, the U.S., Sweden and Norway, with a host of other nations providing surface and air assets in the North Sea theater, where rough sea and weather conditions can make for a difficult operating environment.

Meanwhile, Estonia begins ground exercises involving as many as 13,500 personnel drawn from allied NATO reservists, members of the voluntary Estonian Defense League, and active military.

The chief of the Estonian military, Lieutenant General Riho Terras, said the purpose of the exercise, known as Hedgehog, is aimed at establishing a rapid response unit.

Taking part in the exercise will be infantry from the U.K. and U.S., air defense systems from Belgium and Germany, aircraft from Poland, Dutch soldiers, and integrated Latvian and Lithuanian military units. The U.K. and U.S. will also send aircraft.