On Aug. 6, the Chinese government sent a stealth invasion force sailing into the disputed waters surrounding traditionally Japanese-occupied islands in the East China Sea.

But there wasn’t a single Chinese naval warship among the nearly 250 vessels that swarmed the Senkaku Islands, around 250 miles southwest of Japan. Instead, Beijing deployed 13 coast guard ships, some of them armed, along with an estimated 230 fishing vessels operated by government-sponsored maritime militiamen.

China has sent ships into disputed waters before, but never on this scale. “The latest developments … do seem to be a potentially significant escalation,” Christopher Hughes, a professor of international politics at the University of Warwick in the United Kingdom, told The Japan Times.

Beijing’s heavy reliance on civilian militia is equally noteworthy—and, for China’s rivals, potentially very worrying. These “little blue men,” as U.S. Naval War College associate professor Andrew Erickson has dubbed them, have become the main combatants in China’s undeclared—and so far mostly bloodless—pseudomilitary campaign of expansion into the East and South China Seas.

Erickson’s nickname for China’s maritime militia references the so-called “little green men,” or incognito soldiers, that Moscow sent into Ukraine to back pro-Russian separatists.

There are clear advantages to mobilizing civilian paramilitaries for what amounts to a military mission, Erickson said. In deploying government-controlled fishermen, Beijing gets “the bonus without the onus” as it tries to forcefully cement its claim to huge, fish- and mineral-rich swathes of the western Pacific.

After all, if China sent heavily-armed warships into waters that another country claimed, the other claimant could respond in kind, deploying armed warships of its own and forcing a confrontation that, at the very least, would get the whole world’s undivided attention.

But in sending fishermen, China both maintains credible deniability regarding its true intentions and has the opportunity to portray the other side as overly forceful—or indeed to turn the tables, and cast the defender as the attacker.

The little blue men have popped up across the China Seas, in waters that China, Japan, Taiwan, The Philippines, Malaysia and Indonesia claim—as well as in the undisputed national waters of Indonesia and Malaysia. “Anyone seeing a pattern here?” Erickson quipped on Twitter.

In 2014, Indonesia began seizing and blowing up intruding Chinese trawlers. And, after a fleet of nearly 100 Chinese trawlers invaded Malaysia’s exclusive economic zone the government there threatened to start sinking Chinese fishing boats it catches in its own waters.

Malaysia and Indonesia are trying to head off Chinese campaigns of maritime expansion before they gain momentum and any degree of international legitimacy. In other regions, China has moved quickly to take advantage of the little blue men’s presence in disputed waters.

In late 2014, Chinese dredging ships followed a fleet of little blue men to the Spratly Islands, just west of The Philippines. Beijing and Manila both claim the Spratlys, but that didn’t stop the Chinese government from piling sand atop several delicate reefs, creating artificial islands and, consequently, killing the reefs. Within a year, Beijing had built airfields, seaports, and military installations on seven new, artificial islands.

Manila took Beijing to court, and in July of this year, an international tribunal rejected China’s claim to the South China Seas. But by then the deed was done.

The Chinese military shrugged off, and even mocked, the tribunal’s verdict, and began flying bombers and fighter jets over the islands.

And when the U.S. Navy destroyer USS Lassen sailed through international waters near the Spratlys in October, trawlers crewed by little blue men maneuvered dangerously close to the warship, even crossing in front of its bow, risking a collision.

Twice in May and June, Chinese fighter planes intercepted U.S. military reconnaissance planes flying in international air space in the East and South China Seas. The Americans crews claimed the Chinese pilots flew dangerously close to the U.S. planes.

When the Pentagon protested, the Chinese foreign ministry shot back. The Americans’ aerial reconnaissance “undermines China’s maritime security,” ministry spokesman Hong Lei said.

In a foreboding message to the Chinese people in the aftermath of the tribunal’s ruling on China’s South China Seas claims, Chinese defense minister Chang Wanquan called for a “people’s war at sea” in order to preserve Chinese sovereignty.

Japan is clearly worried that Beijing could move on the Senkakus, which the Chinese call the Diaoyus, the same way Beijing successfully occupied the Spratlys. The Senkakus are currently uninhabited but have, over the last couple of centuries, periodically hosted some small Japanese commercial enterprises. Japan formally reiterated its claim on the islands back in 2012.

It certainly didn’t help calm Japanese officials’ nerves when, in early August, their forces detected a radar aboard a Chinese oil rig positioned near disputed waters in the East China Sea. Japanese media described the rig as a potential military base.

A day after the mixed fleet of Chinese coast guard ships and little blue men swarmed the Senkakus, Japan’s vice minister of foreign affairs Shinsuke Sugiyama lodged a protest with Cheng Yonghua, China’s ambassador to Japan demanding that Chinese vessels depart the Senkakus.

“China is conducting unilateral activities that further raise tensions on the ground,” the Japanese foreign ministry stated. Chinese incursions “cannot be accepted whatsoever,” the ministry added.

But Japan has not yet sent its own ships to try dislodging the Chinese fleet. If the current invasion of little blue men represents an effort on China’s part to definitively seize the Senkakus, then so far, it could be working.

Beijing perhaps underscored its intentions in the East China Sea with a nice bit of military propaganda. On Monday, Chinese censors let leak a clear photo of China’s first homemade aircraft carrier, currently under construction at a shipyard in northern China.

Once complete, the carrier could be the most powerful non-American warship in the Pacific. The photo serves a reminder that China is growing in power and influence—and that it’s building a fleet to match its aspirations.

But when Beijing wants to take over an island without starting a war, it doesn’t need a fleet of warships. The little blue men can do the job.