Naval Forces from 10 NATO countries and Sweden have launched a massive anti-submarine exercise in the Norwegian Sea. The two-week exercise, dubbed Dynamic Mongoose, brings together thousands of NATO troops, and dozens of vessels, including submarines, that will practice hunting, attacking and avoiding detection, according to news reports.

This year's annual exercise comes amid rising concerns by NATO that Russia could employ the same tactics in the three Baltic states — Latvia, Lithuania and Estonia — that it used in Ukraine. The three small countries rely on the Nordic countries for protection.

The exercise follows recent reports of foreign vessels in the sovereign waters of a number of northern European nations. Last month, the Finnish navy chased an "underwater object" believed to be a submarine. It dropped depth charges to warn the intruder it had been detected, according to the Associated Press.

As NPR reported earlier, Sweden launched a hunt for a possible Russian submarine operating clandestinely in Swedish waters last October. It was the largest submarine hunt since the Cold War.

Kai Nickelsdorg, the commander of Germany's U33 submarine, told the Stars and Stripesmilitary newspaper that the art of hunting submarines "is the most difficult task in all of naval and NATO tasks."

Rear Adm. Brad Williamson, the commander of the NATO exercise, said Russia had a right to be at sea, just as the NATO nations do. "But the incidents we have seen are not in line with international regulations ... and that's been the cause of concern," he said, according to Reuters.

U.S. Naval officials say Dynamic Mongoose isn't intended to send a message to any particular country, according to Stars and Stripes.

"We're aware of the incidents that have happened in some of our partner nations' waters," said Williamson, the NATO commander. "I think for us what it does is it focuses our efforts and our training here," according to Stars and Stripes.

The vessels — above and below the water — will practice mastering tactics before moving into drawn-out scenarios, which could include protecting an oil tanker or supply ship that might make for an appealing torpedo target, Williamson said.

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