A video shows a behind-the-scenes look in the control room of a 7,000 ton nuclear-powered attack submarine as it breaks through a thick layer of polar ice in the Beaufort Sea, Popular Mechanics reported Tuesday.

The USS Hartford surfaced north of the Canadian mainland to participate in the U.S. Military’s ICEX 2018, a biennal ice exercise designed to maintain artic navigation and survival skills among U.S. forces, the report said.

A graphic also shows the submarine’s angle of descent.

“From a military, geographic, and scientific perspective, the Arctic Ocean is truly unique, and remains one of the most challenging ocean environments on earth,” Navy Rear Admiral James Pitts, commander of the Undersea Warfighting Development Center, said on the Department of Defense's website.

Along with the USS Hartford, the USS Connecticut also surfaced in the Arctic Circle north of Alaska during the multinational maritime Ice Exercise on March 10, the Defense Department reported.

It is reportedly a hazardous mission for submarines to travel under ice, only smashing through it when they need to surface. The submarine must navigate around “constantly shifting underwater ice formations,” the report said. But a well-trained crew can make it happen.

Popular Mechanics compared the USS Hartford breeaking through several feet of ice to a hot knife cutting though butter.

U.S. nuclear submarines have been transiting through polar waters for sixty years, the report said. In August 1958, the first nuclear-powered sub passed under the North Pole.