– Army helicopters began flying in and out of the scraggly wilderness near this fishing town in August, surprising even the mayor.

The tan, twin-rotor Chinook aircraft thumped over treeless cliffs and the historic port of Dutch Harbor, parking at a mountainside airstrip too small to land jet airliners.

Unalaska’s mayor, Frank Kelty, said he called the military to find out what was going on but learned little.

“We have these Army helicopters here, and we don’t know what they’re doing or where they’re going,” he said after driving by the airport on the remote Aleutian island and seeing a Chinook resting near the runway.

The mysterious operation was part of the U.S. military’s gradual growth in the Arctic as it grapples with the effects of melting polar ice and Russia’s and China’s increasing assertiveness in the region. The slowly evolving plan has included stationing more fighter jets in Alaska, expanding partnerships with Nordic militaries, increasing cold-weather training and designing a new class of icebreaker ship for the Coast Guard that could be armed.

The vision could take greater shape by the end of the year: Both the Navy and Coast Guard are working on new Arctic strategies in light of the quickly changing circumstances senior U.S. military officials see.

In October, the USS Harry S. Truman aircraft carrier and its associated ships sailed above the Arctic Circle, the first such unit to do so since the Cold War. The strike group practiced cold-weather operations in the Norwegian Sea, an area where Russian submarines operate.

“Certainly America has got to up its game in the Arctic. There’s no doubt about that,” Defense Secretary Jim Mattis said during a visit to Alaska in June. “The reality is that we’re going to have to deal with the developing Arctic, and it is developing.”

Recent upgrades include new sensors on several Aleutian islands for a radar network known as the North Warning System. It was first installed during the Cold War to watch for incoming aircraft and ballistic missiles, but the Pentagon concluded more recently that existing radar did not offer “adequate detection and identification of aircraft operating outside the continental United States,” according to an Air Force assessment.

That prompted the operation involving the helicopters in Unalaska.

A military spokeswoman, Leah Garton, said the mission allowed the aircrews to practice navigating over water and landing in mountainous areas, where the sensors were installed. The new equipment will “assist in flight safety for all civilian and military aircraft in the local area,” she said.

The new Navy and Coast Guard Arctic strategies would follow the national defense strategy released by Mattis in January that made countering Russia and China a priority. Both nations have shown interest in Arctic resources as the ice melts, including fossil fuels, diamonds and metals like nickel and platinum.

Russia has more than 40 icebreakers — the U.S. military has two working ones — and has stationed more troops in the region. China, meanwhile, is building its third polar icebreaker and staked a claim this year as a “near-Arctic” state, further injecting itself into policy debates.

“We’re obviously watching both the Russians and the Chinese quite closely,” said Vice Adm. Linda Fagan, who oversees Coast Guard operations in the Arctic and Pacific. “Russia, on their side of the Arctic in sort of the Northern Sea Route, is investing heavily in commercial infrastructure and in military infrastructure.”

Coast Guard Capt. Gregory Tlapa, who commands the lone U.S. military icebreaker traveling to the Arctic each year, said waterways like the frosty Bering Strait are not yet busy with ships, especially when compared with other maritime corridors. Waters are warming, he said, but “somewhat warmer still means mostly frozen.”

But the lack of U.S. military vessels and infrastructure in the Arctic could be problematic, said Tlapa, speaking on the red-hulled USCGC Healy while it refueled in Dutch Harbor in August. Congress recently approved initial funding for six new polar icebreakers, but they are probably still years away from deploying.

“It’s that school of international realism: If you’re not here, someone else will be,” Tlapa said. “The nation doesn’t have a deep-bench strength in terms of capabilities to operate up here and project power and protect our national interests.”

The potential militarization has raised hope for investment in places like Unalaska and Nome, a port town on Alaska’s western coast.

Unalaska, with nearly 5,000 full-time residents, is perhaps best known as the port in Discovery Channel’s “Deadliest Catch” series.

The town — which takes its name from the Aleut word “Ounalashka,” meaning “near the peninsula” — has struggled with unemployment, but Kelty said that has improved in recent years as the number of full-time residents increases and the success of the fishing industry has helped bankroll paved roads, schools and other municipal projects.

Though nothing is planned, Kelty said an influx of U.S. troops could bring infrastructure projects that could benefit residents, such as the installation of undersea fiber-optic cables from mainland Alaska that could bring more affordable internet and cellphone service.

Despite its distance from the Arctic, Unalaska is the last deepwater port where large ships heading to the Arctic can refuel in the western United States, and the first when returning. However, it is not considered ideal by mariners and pilots because of its limitations, which include no highway connecting it to mainland Alaska, limited communications and wild weather in which thick fog and high winds are common and can maroon visitors for days.

Elsewhere in the Arctic, the Pentagon has begun to expand its presence through training exercises with partner nations. In Europe, the Marine Corps is deepening relationships with Norway, Finland and Sweden, training units of rank-and-file troops in the shadow of Russia. In June, Norway’s government asked the United States to increase the number of Marines there from about 330 to 700, with plans to base them on a rotational basis in the Norwegian Arctic.

Russia vaguely warned Norway that there will be “consequences” to the decision, and U.S. and Norwegian officials have sought to stress that the arrangement is meant to deepen their security partnership and build expertise on existing Arctic training ranges, rather than deter Russian aggression.

Col. John Carroll, the deputy commander of Marine Corps Forces Europe, said commanders want to make sure service members are familiar with the biting cold and can move through the countryside on skis or snowshoes.

“Everything is hard. Everything is more difficult,” Carroll said. “When the wind is blowing at freakin’ 30 miles per hour, it’s dark 24/7, and it’s minus-20 degrees Fahrenheit, and you’ve got to put your gear in your pack, get out of your rack, get out of your sleeping bag, get outside the tent and go do something — everything is hard.”