Japanese troops in a joint amphibious exercise with U.S., British and French forces on Guam last year.
ASAKA, Japan—For the first time since World War II, Japan’s army is a unified fighting force.
On Wednesday, a central command station for Japan’s Ground Self-Defense Force opened at a military base here, just north of Tokyo. The headquarters will control Japan’s five regional armies and a new amphibious brigade similar to the U.S. Marine Corps.
The organizational shake-up is among the biggest in Japan’s postwar military history. The army, disbanded in 1945, was re-established nine years later but split into five to thwart a repeat of the conspiracy of senior army officers that helped propel the country into World War II.
In recent years, however, rising security threats, such as China’s challenge to Japan’s southern islands, have prompted government officials to highlight the splintered leadership as a weakness that would hinder quick and comprehensive deployment in a crisis. The navy and air force each has a unified command.
Hours before the command station opened, Japan reported seeing Chinese coast guard ships sailing for the third successive day in waters near East China Sea islands controlled by Tokyo but claimed by Beijing. China calls the uninhabited islands Diaoyu and Japan refers to them as the Senkakus.
China’s “unilateral escalation is a matter of strong concern,” Defense Minister Itsunori Onodera said in a speech to mark the opening of the combined army command.
The new Japan Ground Self-Defense Force central command will also eliminate the need for the U.S. military to deal with several local counterparts for operations in Japan. Around 50,000 U.S. troops are based in Japan under a security-treaty alliance.
Japanese Prime Minister Shinzo Abe, here reviewing the Self-Defense Forces in 2016, has been an advocate for the military since taking office in 2012, raising spending for six straight years and easing restrictions on its scope of action.
“This will simplify coordination between the U.S. Army and the [Japanese army] during a natural-disaster or security situation, since the same procedures will be used during training, exercises, or crisis, anywhere in Japan,” said U.S. Army Japan deputy commander Col. Stephen J. Grabski.
The creation of the new command is part of a broad review and upgrade of Japan’s Self-Defense Forces, which many Japanese still associate more with disaster relief than warfare.
Though far smaller than most regional rivals, Japan’s military is equipped with some of the world’s most advanced weaponry. The country is investing in cruise missiles, at least 42 advanced F-35 fighter jets and a new missile-defense shield. Last month, the ruling Liberal Democratic Party called for the nation to develop its own aircraft carrier.
Much of Japan’s military equipment is American-made, and U.S. President Donald Trump has urged Tokyo to buy more.
In recent years Prime Minister Shinzo Abe has pushed through legal changes to loosen restrictions on the military, including allowing it to fight in support of an ally under attack near Japan. He has set a target of 2020 for introducing a constitutional amendment establishing Japan’s right to maintain its own armed forces. Taken literally, the postwar constitution bars a military, though previous governments haven’t questioned the armed forces’ legitimacy.
Government and military officials say Japan faces the most security threats in decades, including from North Korean missiles, and have no choice but to respond.
“We have to create a truly combat-ready Ground Self-Defense Force,” Maj. Gen. Tadao Maeda, a senior army official responsible for planning the transition, said in an interview.
Japan’s primary fear is that China may try to seize the Senkaku islands. To be better able to retake any islands, the army is tripling its amphibious unit to 2,100 troops. Japanese soldiers have trained with U.S. Marines for around a decade in amphibious warfare.
A Chinese foreign ministry spokesman didn’t directly answer a question about Japan’s central army command, but China often has criticized Japan’s military changes, calling on Tokyo not to repeat past mistakes.
Some defense experts say that while the expanded amphibious unit and single army command improve Japan’s capabilities, spending on the military spending is sometimes misguided and coordination between land, sea and air forces is still insufficient.
Jeffrey Hornung, an Japan security specialist at Rand Corp., points to the acquisition of destroyers and submarines rather than modern amphibious-troop carriers needed to carry soldiers into battle, and to the Air Self-Defense Force’s lack of training in close air support.
Following a ceremony to open the new army command, Mr. Onodera said the government is emphasizing joint operations of the three arms of the military to deal with crises such as ballistic-missile attacks, island defense or large-scale disasters.
Mr. Onodera also said there are sufficient checks against military usurpation of political power, as in the past.
“We have firm civilian control,” he said.
WSJ