Alarmed by a Chinese move last year to send a fleet through the Miyako Channel 1,700 km south of Tokyo and into the open waters of the Pacific Ocean for maneuvers, Japan is deploying self-defense forces to an island that overlooks the strategic channel.

Japan’s redeployment also stems from concerns over increasing Chinese assertiveness over the disputed Senkaku chain, known as the Daioyutai to the Chinese. The deployment has not only upset the Chinese but unsettled the Taiwanese as well.

The deployment, to Yonaguni Island, is part of a general trend of transferring forces from Japan's northern region to the extreme southern flank. The decision to install the 100-man unit, estimated to cost ¥1.5 billion (US$20 million) and expected to be completed by 2015, is part of a growing trend by the nations that surround China to tighten up their defenses as they increasingly side against what they perceive as the growing belligerence of the region’s biggest country.

Yonaguni, only 28.8 sq. km in size and with a population of 1,700, overlooks the 300-km gap in the so-called First Island Chain, a maritime line running between Japan, Taiwan, the Philippines, Vietnam and Indonesia – all of which would potentially side with the US in case of war with China. If the situation were to turn sour in the West Pacific, it's the Miyako Channel where the US, Chinese and Japanese navies would likely grind together.

While the deployment has been greeted with anger in Beijing, it has also led to concern in Taipei. The island is so close to Taiwan’s east coast that seamen say on a good day they can see it, roughly 100 km east of Taiwan’s eastern town of Hualien.

Yonaguni is close to the resource-rich and strategic regions in the East China Sea that are disputed by Tokyo, Beijing and Taipei, such as the Japanese-controlled Senkaku Islands (Diaoyutai in Mandarin), which in 2010 witnessed the Japanese seizure of a Chinese fishing vessel for trespassing, setting off a major Sino-Japanese row that culminated in a Chinese threat to cut off rare metals shipments for Japanese industry.

Observers say the Yonaguni deployment was chosen in this context. They say Tokyo thinks Beijing's rationale for claiming Senkaku – Chinese fishermen have visited it from time immemorial – could just as easily apply to any of Japan's southern islands, and therefore is shifting its defensive focus from guarding against a Soviet or Russian attack to one coming from China.

Aside from a small contingent on Miyako, the southern islands have been totally demilitarized and vulnerable. The deployment of a so-called coastal monitoring unit can be seen as a means of asserting Japanese sovereignty over islands in a region of conflicting claims.

The first time Japanese military plans involving Yonaguni made headlines in Taiwan was in June 2010. Tokyo had snubbed Taipei by extending its Air Defense Identification Zone (ADIZ) – an area where entering aircraft are obliged to radio their intended flight course to the respective country's air traffic controllers – from Yonaguni westwards by 22 km at Taiwan's expense without having given the long-time de facto ally a heads-up. At that time, observers close to Taiwan’s opposition anti-unification Democratic Progressive Party (DPP) saw the move as a sign that President Ma Ying-jeou’s Beijing-friendly policies had distanced Taiwan from the US and Japan, and that Tokyo had accordingly lost its trust in Taipei.

In a recent interview with Asia Sentinel, Lai I-chung, a member of the research body the Taiwan Thinktank, still supported that notion. By strengthening Yonaguni, he said, Japan hasn't so much got Senkaku in mind as hedging at a time when Taiwan is perceived as increasingly falling into China's hands and thus ceases to function as a buffer.

“The decision was already made when Taro Aso was prime minister (Sept. 2008-Sept. 2009) before the flare-up of the Senkaku dispute,” Lai said. Yonaguni's location – well south of Senkaku – suggests that there's no direct connection with that issue. Also, he said, during a possible China-Japan conflict, Yonaguni itself would be shielded by Taiwan anyway.

“It could be Japan's uneasiness with Ma's China-leaning foreign policy. The waters east of Taiwan have become of concern for Japan in recent years, and the frequency of Chinese vessels and aircraft appearing there has significantly been increasing,” Lai said.

Unsurprisingly the Chinese have their own interpretation. Beijing regards Japanese expenditure on maritime construction and reinforcing of islands in the context of Tokyo's covert quest to get rid of the constraints of its Peace Constitution, imposed on the country by the US after its defeat in World War II.

In a recent article published in the PLA Daily, the official daily of the People's Liberation Army, author Liu Liqun listed the deployment on Yonaguni in one breath with Japan's plans to start construction of two helicopter carriers in 2012, the general stockpiling and updating of military technology, the sending of warships to provide logistical support and oil to the US military, as well as the employment of anti-submarine patrol aircraft to cruise the Gulf of Aden.

“These moves to advance Japan's open-ocean strategy completely lay bare Japan's aggressive posture. When Japan's Maritime Self-Defense Force was first established, it was just a small naval force to be used for coastal defense. Now, however, it has become the most formidable maritime armed force in Asia, excluding the US Navy,” Liu wrote.

“By deploying the Self-Defense Force to islands in the southwest, […], Japan is going in a dangerous direction.”

Observers say the move's importance is out of proportion to the small numbers. James Holmes, an associate professor at the US Naval War College, said the decision is kills not only two birds with a stone but most likely quite a few more.

“Defending the island itself will obviously be a major purpose of any deployment; stationing forces there would signal China that it couldn't quickly or easily seize it. That's valuable in itself,” Holmes said. “But the passages around the island are also important.”

It was through this passage that Chinese fleet consisting of two guided missile destroyers, three frigates, two Kilo-class submarines and one supply ship crossed the strait in April of 2010 to hold sea-air joint anti-submarine warfare drills near the Okinotorishima Reef. During the exercise, China's ship-borne helicopters once came as close as 90 meters to a Japan Maritime Self-Defense Force ship. The reef lies midway between Taiwan and Guam, home to a major US naval base. Japanese media speculated that China's ships used the drills to map the ocean's bottom over which the US Pacific Fleet would pass in future conflicts on its way to Taiwan.

“Anti-ship missiles positioned on Yonaguni could help close nearby straits to Chinese warships,” Holmes said. “This would ease the pressure on the Japanese or Taiwanese east coasts, helping US forces steaming westward gain access to the region. A well-designed force deployment at Yonaguni could provide disproportionate bang for the buck.”