TOKYO — Japan is taking another step closer to fielding a Marine Corps-like brigade that would defend its southwestern territory, amid increasing tensions with China over who rightfully owns islands in the East China Sea.

A combined U.S.-Japan scenario in the Northern Marianas to retake an island during the Keen Sword exercise this week represents a major philosophical shift — one that some military analysts say is overdue — from the land-focused strategy long employed by Japan’s Self-Defense Forces.

The 2,100-member Amphibious Rapid Deployment Brigade, planned for activation by March 2018, could be used for various missions, including quicker humanitarian relief after a natural disaster.

But analysts say its deterrent effect against Chinese claims on Japan-controlled territory will be the brigade’s greatest contribution.

Beijing has deemed the Japan-administered Senkaku Islands an “indisputable” part of China and declared an air defense identification zone over them in 2013.

The U.S. is obligated to defend the Senkakus and any other Japanese territory under the terms of a security treaty with Japan.

Navy officials say privately they wouldn’t be surprised if Chinese intelligence ships monitored Keen Sword from international waters, which they’re entitled to do under the U.S. view of international law.

The Chinese have sent ships near Guam and the Northern Marianas multiple times, including near the USS George Washington carrier strike group during the Valiant Shield exercise in 2014.

If China decides at some future point it is willing to risk the geopolitical fallout of taking Senkaku — or even some of the smaller islands governed by Taiwan, without invading the heavily populated main island — it has the amphibious force to do it.

“A PLA invasion of a medium-sized, better-defended island … is within China’s capabilities,” said the Pentagon’s 2016 report to Congress on China’s military. “Such an invasion would demonstrate military capability and political resolve while achieving tangible territorial gain and simultaneously showing some measure of restraint.”

Japan could provide logistical support from its well-regarded maritime forces if ever invaded, but if it came down to ship-based troops coming ashore, for now they’d be reliant on the U.S.

For decades, Japanese defense strategy was focused on the northern island of Hokkaido, where Japan has stationed multiple divisions and lots of armored vehicles for defense against Russia.

Although Japan and Russia still disagree on ownership of nearby islands occupied by the Soviet Union in the waning days of World War II, relations are warming, said Toshiyuki Shikata, a defense analyst and retired lieutenant general in Japan’s Ground Self-Defense Force.

However, tanks and divisions don’t make sense for the southwestern islands. New tactics must be employed, he said.

“You can’t protect [small] islands,” Shikata said. “The attackers can decide when, where and how large the attack will be. This is common sense in military history … to have the power to be able to take back an island deters [the enemy’s] fighting spirit.”

Japanese ground troops have trained with Marines twice in California, but the Keen Sword amphibious exercise on Tinian island will provide an environment much more like Japan’s tropical southwest islands.

Grant Newsham, a retired Marine colonel and research fellow at the Japan Forum for Strategic Studies in Tokyo, was the first Marine liaison officer to the JSDF and provided input into the amphibious force’s creation.

Combined U.S.-Japan operations went very well at the Dawn Blitz exercise last year in California, he said.

But ask Newsham how Japan would do on its own if staging an amphibious operation, and the answer is: “not very well.”

The problem is that the ground, air and sea services don’t practice operating together much and don’t communicate well with one another, he said.

For example, the ground force will be relying on the maritime force’s ship, but they put the brigade together without directly coordinating, Newsham said.

This would not happen with a Marine Expeditionary Unit, which the Japanese brigade will closely resemble, minus fixed-wing aircraft and heavy artillery.

Japan’s problem isn’t entirely unique. Many of the world’s forces have difficulty with joint communication when funding is scarce and each service is competing against the others, Newsham said. Resistance to change plays a role as well, he said.

“But it also is symptomatic of the general ‘restraint’ on the JSDF that’s existed since the time of founding, and that prevented it from becoming a full-fledged military — even though it has all the hardware, troops and other trappings of a military,” Newsham said.

A senior official who publicly advocated closer communication between the branches would likely pay a political price in Japan, he added.

The lessons of WWII and Japan’s post-war constitution have made many deeply distrustful of expanding the Self-Defense Forces’ role. A measure last year that would allow Japan to defend close allies in combat passed into law over majority public opposition.

Repeated training in the Northern Marianas, a U.S. commonwealth, would squeeze the Japanese budget less than traveling to California, while helping it get the practice it needs to operate effectively, Newsham said.

Operations closer to home also provide the Asia-Pacific region with a visible indicator of the U.S.-Japan alliance’s strength, Shikata added.

The exercise “shows that the U.S. is watching Japan’s back,” he said. “This is the best tactic for defending [Japan’s] islands.”

Stars and Stripes staffer Hana Kusumoto contributed to this report.

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