When a half-dozen Chinese patrol vessels entered Japanese waters 14 months ago, Japan’s then-prime minister called an emergency meeting. The Chinese ambassador in Tokyo was summoned for a tongue-lashing. A Japanese government spokesman described the move as an “invasion” of “unprecedented scale.”

The vessels eventually backtracked, but the episode signaled the first stage of China’s fundamental maritime strategy — one in which it forges into new areas, withstands the initial fury, and turns groundbreaking gambits into commonplace activity. In most cases, the strategy has worked. Chinese boats now cut through waters around Japan-administered islands almost weekly, drawing complaints from Tokyo but not alarm.

For Japan, China’s piecemeal advance through contested territory represents perhaps its greatest defense challenge since the end of World War II. Although several Asian nations have tried to curb China’s expansionist ambitions, some experts feel Japan is best-equipped for the task: led by a hawkish prime minister, powered by a reviving economy and backed militarily by the United States.

But despite ongoing upgrades to its aircraft and patrol boats and increased coordination with Washington, Japan has yet to find an answer for its increasingly powerful neighbor. Officials here say China continues to push boundaries, sending fighter jets closer to Japanese shores and last week declaring a new air defense identification zone over the East China Sea.

None of China’s moves, by design, has been provocative enough to spark an armed skirmish. That partly explains why deterring China has been so vexing for others in the region.

In the South China Sea, China has backed the Philippines away from several contested reefs and shoals by sending waves of increasingly powerful vessels to the area. Several Japanese officials and security experts say China is now duplicating that strategy in the East China Sea, but with more intensity because of the frequent use of aircraft.

China is trying to “unilaterally alter the status quo by coercive measures,” Fumio Kishida, Japan’s foreign minister, said in a news conference Friday.

Japan has asked the United Nations’ International Civil Aviation Organization to examine whether China’s new zone threatens aviation in the area, its Foreign Ministry said Saturday. Japan’s move is part of its broader strategy of appealing for international support in dealing with China.

Chinese officials portray their moves as responses to Japanese provocations, particularly Tokyo’s purchase in September 2012 of three contested islets from a private landowner.

But Japanese officials say China’s ambitions at sea go back well before that date, and they point to a several-year trend of Chinese activity in the East China Sea. In 2004, Japanese scrambles against Chinese aircraft occurred roughly monthly, according to Ministry of Defense statistics. By 2007, they happened almost weekly. This year, they’re happening more than once a day on average.

Two months ago, an unmanned aerial vehicle was spotted for the first time above the islets. A Japanese Ministry of Defense press official said that its origin hasn’t been identified, but “if you take its flight path into consideration, it is possible to suspect it is a drone of China.”

The trend “testifies to a long-term increase in Chinese military activity in the maritime domain,” a Foreign Ministry official said, speaking on the condition of anonymity to discuss the situation.

Japan’s military limited

As China has increased its maritime presence over the past half-decade, Japan has had to catch up. Until several years ago, Japanese leaders almost never described China as a threat. Through 2010, Japan’s Self-Defense Forces were positioned primarily to defend against a Russian invasion from the north.

Japan’s reversal has been swift. A new defense strategy three years ago reorganized troops, placing more emphasis on perimeter islands. Japan is now updating that strategy, and initial recommendations call for the introduction of a Marines-like unit and the eventual use of drones for surveillance.

The Defense Ministry’s budget request for 2014 calls for upgrades to surveillance equipment and the purchase of new patrol aircraft. Although China’s announcement last week of its air defense identification zone threw a spotlight on the airspace above the East China Sea, much of Japan’s spending was already geared to aircraft upgrades. The Air Self-Defense Force budget is set to rise 7 percent in 2014.

Japan has some of the world’s most modern technology for surveillance and deterrence, military experts say. But its problem would come if there were an armed conflict, because Japan is barred by its pacifist constitution from having key offensive weapons such as long-range missiles and traditional aircraft carriers. Japan’s largest ship, the Izumo-class destroyer, can carry only helicopters.

“That’s definitely a weakness,” said Masashi Nishihara, president of the Research Institute for Peace and Security in Tokyo.

Before taking office one year ago, Prime Minister Shinzo Abe talked about removing some restrictions on the military. But that would require contentious constitutional revisions, and Abe, in office, has instead channeled his energy into patching up relations with other countries in the region who were ignored by his predecessors. Abe has visited every member of the Association of Southeast Asian Nations in what some experts say is an attempt to isolate China.

War of words

China and Japan have been hawking dueling narratives about their conflict. Military expert Li Jie told China’s Global Times that the United States and Japan had been “defiant” in refusing to cooperate with the Chinese edict that all aircraft in the new aerial zone relay flight information to Beijing. A separate editorial in the China Daily said Beijing has every right to adopt an “internationally common practice.”

Japan, meantime, has said it’s taking a stand against a “unilateral” move and that other countries should share Japan’s concerns about freedom of navigation in international airspace.

In the short term, some experts in Tokyo say, China’s announced aerial zone might have backfired, drawing strong rebukes from Australia, South Korea and the European Union and prompting a flyover of unarmed U.S. B-52 bombers.

But the real test for China’s strategy will come after the initial shock has waned.

“For the time being, things seem to be quite favorable to us,” said Narushige Michishita, an associate professor at the National Graduate Institute for Policy Studies in Tokyo. “But the question is how long this will last. China has been creating a gradual fait accompli, step by step, which is a pretty smart tactic. We make a big deal of this now, but we’ll forget about it after a while.”

Yuki Oda contributed to this report.