Groton — The USS Hartford returned this week from a five-week Navy exercise off Alaska's north coast that tested the submarine's ability to shoot and recover torpedoes beneath Arctic sea ice.

"The United States has significant national security and economic interests in the Arctic. The submarine force must be able to demonstrate its ability to preserve and protect those interests as we have for more than 60 years," Cmdr. Matt Fanning, Hartford's commanding officer, said in a recent email.

The Hartford, a Los Angeles-class attack submarine based in Groton, was one of two U.S. submarines to participate in the biennial exercise, known as ICEX, that tests the Navy's ability to operate in the Arctic. The UK Royal Navy submarine HMS Trenchant also was on hand. The boats conducted multiple arctic transits, surfaced in the North Pole and helped collect scientific data to advance understanding of the Arctic environment, and other training.

The exercise, which cost upward of $8 million, is "important because it gets us new information about how to operate in that environment but it's also symbolic in that it translates to we care about the Arctic and we're going to be present there," U.S. Sen. Chris Murphy, D-Conn., told The Day recently.

News reports have detailed Russia's military buildup in the Arctic. China also is staking a claim in the region. However, officials maintain there's more cooperation than conflict in the region.

The Hartford and the USS Connecticut from Bangor, Wash., each fired several training torpedoes during the exercise to test advancements made to the weapons system for the under-ice environment. The torpedoes had no warheads and carried minimal fuel, according to the Navy.

"The data we collect from these tests drives constant improvement in the torpedo while giving the submarine force a chance to demonstrate its skill at employing these weapons," Fanning said in his email.

Navy and Coast Guard divers recovered the torpedoes, which were lifted by helicopter out of holes drilled in the ice.

The Hartford spent several weeks preparing for the exercise — checking everything from calibration and use of special sonar systems that detect ice keels to training on how to cut the ship's hatches out of the ice, Fanning said. The crew also received help and training from a specialized ice pilot that was on board.

About 20 percent of the current crew were on board when the Hartford participated in the exercise two years ago. Those who went through the exercise before — "they call it 'TWICEX,'" Fanning said — helped inform their shipmates about what to expect. Hartford was selected to participate again, given where it was in its operational schedule.

The submarine force has a history of operating in the Arctic. The USS Skate, after which the temporary ice camp set up during the exercise was named, became the first submarine to surface at the North Pole on Aug. 11, 1958.

j.bergman@theday.com