The U.S. Army in the Pacific envisions becoming a more agile force capable of rotating thousands of mainland troops to the region on short notice and setting up temporary outposts in allied nations or on some of the 25,000 islands that surround the South China Sea to fire missiles at adversary ships and bases.

That capability will come through what’s known as Multi-Domain Operations — the ability to mesh abilities across services and use that as a force multiplier on land, sea, air, space and cyberspace. The approach represents the most fundamen- tal rewrite of how the Army will fight in several decades.

Gen. Robert Brown, commander of U.S. Army Pacific, met Tuesday at Fort Shafter with Adm. Phil Davidson, head of U.S. Indo-Pacific Command, Army Vice Chief Gen. James McConville and Army Undersecretary Ryan McCarthy to chart the Army’s course ahead in a time of fast-paced change.

“Great power” competition with China and Russia is driving the changes.

“What the United States or Americans might not be used to is the ability to get there fast, (which has) become significantly important,” Lt. Gen. Eric Wesley, director of the Army Futures Command’s Futures and Concepts Center, said Tuesday at a media roundtable.

Brown noted that during World War II, 22 Army divisions fought across the Pacific, with air and sea forces enabling the Army and Marines to seize land as the United States leapfrogged across the vast region.

China’s long-range missiles now threaten the ability of Navy ships and Air Force aircraft to get within fighting distance, but Army ground-based missiles can help with the fight.

“Now land enables air and maritime, whereas in World War II it was the opposite,” Brown said.

The Army’s 2020 proposed budget calls for funding two large exercises in Europe and the Pacific called Defender Europe and Defender Pacific, DefenseNews.com reported.

Brown said the 91,000 soldiers based in the Pacific will remain here, but the total will be temporarily augmented under Defender Pacific by soldiers brought in from the mainland.

The plan is for a division headquarters and several brigades to participate, with 5,000 to 10,000 soldiers rotating through the region, Brown said. The number will depend on the scenario and exercise, he said.

Brown noted the “hyper competition” occurring in the Pacific, adding, “China is the priority.”

Susanna Blume, with the Center for a New American Security, wrote last year that a return to strategic competition against China and Russia — who both have the technology to challenge the U.S. military’s ability to operate freely — requires the Pentagon to think differently about the way it uses its forces.

“To compete effectively against China and Russia while maintaining commitments in the Middle East, the Defense Department will need to figure out how to maximize the strategic impact of the size and capability of the force it has now” — by developing a new force employment model, Blume said.

The U.S. military has talked to allies about Multi-Domain Operations, and Japan is using the concept, Brown said.

McConville said the Army is “not at the point of saying we’re going to put long-range” weapons in friendly countries. But he added, “I think they are open to the discussion.”

The range of weaponry could include long-range artillery and hypersonic missiles that reach speeds greater than Mach 5.

Any conflict in the Pacific — South China Sea or elsewhere — would be a joint- service problem, Brown said. “The Army would have a role in any issue that would develop in the South China Sea. All of the forces are going to have to work together to be successful to handle that,” he said.

U.S. Army Pacific already has made history with Multi-Domain Operations, meanwhile.

In July during Rim of the Pacific exercises, the Army fired a Naval Strike Missile from a truck at the Pacific Missile Range Facility on Kaui and hit a decommissioned Navy ship at sea.

Ally Japan fired its own truck-mounted Type 12 anti­-ship missiles at the ship. Brown said then it was the first time Japanese Ground Self-Defense Force missiles were under U.S. fire control while working with U.S. forces — including the Army, Navy and Air Force — to target a ship.