First came the whistle, then the thud and the plumes of dust as the “mortar” landed in the area where the “enemy” had been spotted.

The Japanese soldiers, having bundled out of tanks so they could lie in wait behind clumps of tall grass, then let loose. Two American Apache helicopters came in low to avoid detection, then suddenly soared up to (pretend to) unleash their weaponry on the enemy forces.

Loudspeakers along the side of the field, which sounded like World War II relics, crackled out radio chatter in Japanese and English. “We have eyes on the enemy tank,” an American voice said.

It’s not war, or even a very close resemblance to war. But in a region of the world where there are enough territorial disputes on the islands surrounding Japan that battle sometimes feels possible, this is an exercise that reveals two military forces looking to redefine their mission. One is American, the other Japanese.

On a recent fall day, with fresh snow on the mountains here on the northern island of Hokkaido, American and Japanese soldiers were learning how to work together with different equipment, capabilities and languages.

The Orient Shield exercises, the latest iteration of which were held on this Japanese military base, ended Friday.

They are taking place at a time of immense change for both militaries: The Japan Self-Defense Forces, as they are officially called, are gearing up to take on a bigger role in the region and expand their capabilities.

Japan’s conservative prime minister, Shinzo Abe, has been championing a reinterpretation of Japan’s postwar pacifist constitution to allow the military more scope to act, including being able to aid its main ally, the United States.

Abe considers this a first step toward Japan finally shrugging off its wartime legacy and becoming a more “normal” country.

At the same time, the U.S. Army is seeking ways to remain relevant as the military “pivots” toward Asia, where across a vast region battles would be fought in the air or at sea — in an era, moreover, of increasing public aversion to putting boots on the ground.

“The U.S. is in a quandary over what to do with its land forces,” said Patrick Cronin of the Center for a New American Security. “What is the role of ground forces when everyone’s focused on air, sea and cyber?”

Such questions are being asked amid budget cuts and an inward turn at home.

The Pentagon has announced plans to cut Army numbers to 450,000 troops, down from 570,000 at the height of the wars in Iraq and Afghanistan. Only 23,000 troops are deployed in the Asia-Pacific region, and more than 20,000 of them are in South Korea, guarding against the North Korean threat.

At an Association of the U.S. Army conference in Washington last month, military leaders tried to make the case for putting American forces on the ground across the Asia-Pacific region to train and advise allies. Defense Secretary Chuck Hagel suggested a new mission for the Army in this part of the world: as a coastal defense force, drawing on a venerable Army model that has its roots in the War of 1812.

“The premier foreign policy initiative of the Obama administration is the rebalance to the Pacific,” said Scott Harold, an Asia specialist at the Rand Corp. “This has occurred in the context of the fiscal austerity and sequestration that has cut billions of dollars from our defense budget. The way you save your program is to attach yourself to the pivot.”

And part of the Army’s challenge in the region is historical.

Gen. Douglas MacArthur, the American general who oversaw the postwar occupation of Japan and then commanded U.S. troops during the Korean War, spoke out against becoming involved in a land war in Asia.

In 2011, Robert M. Gates, then the defense secretary, echoed that point when addressing Army cadets at West Point.

“The U.S. Army in Japan has a crisis of confidence. Its history is of 1) invading, 2) occupying and 3) fighting the Korean War from here,” Paul Giarra, a former Pentagon expert on Japan who now runs a defense consultancy, said during a recent visit to Tokyo.

“When the U.S. Army left Vietnam, it left Asia behind and, with the exception of a few folks in Korea, hasn’t thought about [East] Asia since. It doesn’t know how to think about Asia,” he said.

Exercises such as Orient Shield are a way to try to make the Army relevant in the Asia-Pacific theater again, analysts said.

Orient Shield was the last stop for the 2nd Stryker Brigade Combat Team from Joint Base Lewis-McChord in Washington state, which carried out exercises in Malaysia, Indonesia and then Japan as part of the Army’s Pacific Pathways initiative. The new concept is designed to help small, agile units deploy quickly around the region.

About 60 percent of the 700 American soldiers taking part in the exercises had never been deployed before. “Hundreds of these kids were in high school last year,” said Col. Louis Zeisman, U.S. commander of the exercise.

About 900 members of Japan’s Ground Self-Defense Force took part, including those from the 7th Armored Division, Japan’s only tank unit.

The exercises focused on bilateral operations and improving combat planning, as well as exposing the new recruits to practical experience. The two forces had separate chains of command, and a big part of the two-week exercises was synchronizing movements.

“We’re figuring out what works and what doesn’t work,” Zeisman said. “We’re working with two different ways of getting to ‘mission accomplished.’ ”

Indeed, the Army believes it has a crucial role to play in Asia.

“If you look on a map, you see a lot of blue, but human beings still live on land,” said Col. Rumi Nielson-Green of the U.S. Army Pacific, based in Hawaii, noting that 50 percent of the world’s population lives on the Pacific Rim.

“The Army is not out here by itself. We’re part of the U.S. Pacific Command . . . and we all have a role to play,” she said.

Although any future conflict in this region would most likely revolve around air and sea battles, Giarra agreed that the Army still has a “gigantic” role in the region.

“If you look at a map and look at the maritime space, there’s an awful lot of land in it,” he said. “The Navy and Air Force can’t operate without controlling the land. I can’t imagine controlling the South China Sea if you don’t control the Philippine land mass.”