The U.S. military tries to fight jointly, meaning cooperatively across services.

But in the future, against adversaries such as China or Russia, the Pentagon will have to amplify that cooperation to win on the battlefield, according to Gen. Robert Brown, head of U.S. Army Pacific at Fort Shafter.

Ten or 15 years ago, the Air Force and Navy probably could have handled a South China Sea or East China Sea challenge without needing too much help from the other services, Brown said at an Association of the U.S. Army forum last month.

“And now they can’t. They just can’t. And they know that, and it’s forcing us to work together,” Brown added.

Greater cooperation is being seen in training in Hawaii and will increasingly characterize it going forward.

A recent example: During Exercise Tropic Koa ACE held Feb. 11 to March 2 on Oahu, Kauai and Hawaii island, mainland Air Force A-10 attack aircraft trained with Hawaii-based tilt-rotor Marine Corps MV-22 Ospreys and AH-1Z Viper helicopters.

An Air Force HC-130J recovery aircraft out of Georgia served in an airborne mission command role, and ground-based Navy, Marine and Air Force attack controllers and Army airstrike observers directed maneuvers and transmitted targets for the A-10s.

Two B-52H Stratofortress bombers were added, flying from Andersen Air Force Base on Guam to test close air support weapons.

Change is being driven by the emergence of China and Russia as peer competitors and strategic rivals whose long-range missile advances pose significant threats to U.S. bases, aircraft and ships.

Brown calls it a period of “hyper competition.” In some areas of technology the United States has fallen behind — such as with hypersonic missiles — while it focused on Iraq and Afghanistan.

But the Army is now retooling for the high-end fight, and that means greater focus on shore-based missiles for defense and the ability to sink ships at sea — while at the same time working hand in hand with the other services to do so.

Long-range firepower is the Army’s No. 1 modernization priority and is seen as critical to winning a fight against a peer adversary.

The Army is pioneering a new fighting concept called multi-domain operations — the ability to mesh abilities across services to use as a force multiplier on land, sea, air, space and cyberspace.

The approach represents the most fundamental rewrite of how the Army fights in several decades and seeks to exploit windows of opportunity on a rapidly evolving battlefield.

“A missile launched from the land can destroy a ship at sea controlled by an Army element using Navy, Air Force, Marines and some national satellite means — things never before used to pull it all together,” Brown said.

Gen. David Goldfein, chief of staff of the Air Force, said at the Brookings Institution in February that it’s the Army and Air Force that are primarily working on multi-domain operations, but the Navy and Marine Corps are discussing it.

The “concept of operations” is expected to become doctrine within about a year, he said.

Goldfein laid out a “visual” of a “penetrating joint team” using F-35 stealth aircraft, satellites, surveillance, special operators and submarines — among other forces — working together.

About $135 billion is in the defense budget to develop the concept, he said. The F-35, which has advanced sensors, can be the “quarterback” of that offense, fusing information from all sources to call “audibles” inside enemy air space, according to Goldfein.

With war-gaming repeatedly showing traditional warfighting doctrine failing in an overseas fight with China or Russia, Brown sees multi-domain operations as a successful way forward.

“All formations will have to become multi-domain or they’ll be irrelevant, (but) it’s going to be years before it can happen,” he told breakingdefense.com in March.

Brown said U.S. forces “are incredibly joint,” but “we’re not joint enough.”

“Episodically, we can pull together capabilities, but it takes weeks, sometimes months,” he said. “It’s got to move from episodic to routine — minutes and hours — where it’s absolutely routine.”

David Ochmanek, an analyst with RAND, which runs many war games, said last month that “in our games, when we fight Russia and China” U.S. forces take a drubbing in those countries’ back yards.

“We lose a lot of people, we lose a lot of equipment, we usually fail to achieve our objective of preventing aggression by the adversary,” he said.

Conversely, in a recent Pentagon war game, “one of the conclusions (was), multi-domain ops works,” Brown said.

The Army “has a significant role” in a future fight in the Pacific with its ability to operate from some of the 25,000 islands in the region, firing missiles at ships in the littorals, or near-shore waters, Brown said.

The four-star general said in September, for the first time in history, a multi-­domain task force will be part of a major exercise, Orient Shield with Japan.

The 17th Field Artillery Brigade out of Washington state will be working with Japanese Ground Self-­Defense forces “to continue to develop and practice the multi-domain concept alongside a key ally in the region,” said Col. Derrick Cheng, a U.S. Army Pacific spokesman.

The Army’s budget request for fiscal 2020 includes more than $600 million to field two Israeli “Iron Dome” air defense batteries and 44 maneuver short-range air defense batteries for Stryker armored vehicles.