Rock, Reef or Red Line?

China tests Japan’s maritime resolve near Okinotori, a speck of Pacific rock with outsized historical and geopolitical weight.

The tiny, uninhabited and nearly invisible Okinotori-shima, a pair of minuscule atolls some 1,700km south of Tokyo, is once again stirring storms in East Asian geopolitics.

Japan recently lodged a formal diplomatic protest after its coastguard observed a Chinese survey vessel deploying a wire-like object into the surrounding waters, 270km east of Okinotori.

Tokyo accused Beijing of conducting unauthorized maritime scientific research within Japan’s exclusive economic zone (EEZ). The Chinese vessel retreated later that evening, but not before reigniting a long-simmering dispute that transcends cartography and drills down into questions of sovereignty, security and shifting power balances in the Indo-Pacific.

Way back in 1931, as an aggressive and militaristic Japan tightened its imperial grip across East Asia, it formally claimed Okinotori-shima. At the time, Japan’s imperial navy had envisioned them as a remote watchtower in the Philippine Sea, guarding the maritime corridor to Micronesia and beyond. After defeat in the Second World War, Japan retained administrative control over the atoll, though the United States took up the regional security mantle. Today, that same rock finds itself at the centre of another contest for power in the Pacific.

UNCLOS, the United Nations Convention on the Law of the Sea, permits coastal states to claim a 200-nautical mile EEZ around islands capable of sustaining human habitation or economic life. Tokyo has poured millions into preserving Okinotori’s legal status as an island. In the early 2000s, it reinforced the coral reef with titanium nets, concrete walls and even artificially planted coral to prevent it from disappearing under the waves. Japan maintains a weather station and maritime monitoring facilities there, partly as symbolic sovereignty and partly as practical strategy. If it loses the legal argument, it forfeits claims to a 400,000 square kilometre swath of ocean - an area roughly the size of Germany.

China’s encroachment must be understood in light of its broader maritime ambitions. Since the early 2000s, Beijing has steadily expanded its reach in the Western Pacific, constructing artificial islands in the South China Sea and asserting ‘historic rights’ far beyond internationally recognised limits. The Philippines took Beijing to court and won in 2016 when UNCLOS’s arbitration tribunal ruled that China’s claims lacked legal foundation.

But Beijing simply ignored the ruling. It has since continued to press its advantage, not through overt force but through strategic ambiguity via coastguard patrols, fishing fleets and ‘scientific research’ vessels operating just on the edge of confrontation.

This maritime salami-slicing of pushing boundaries without triggering war has become a signature of the Chinese strategy of trying to wear down the resolve of its rivals and normalise its presence in disputed areas. The same tactic is now visible near Okinotori. Just as it has turned coral reefs into fortresses in the South China Sea, China may be testing Japan’s willingness to enforce its maritime rights far from its main islands.

The history of Japanese maritime posture adds another layer of complexity. In the decades after World War II, Japan renounced war but built up a formidable coastguard and maritime self-defence force, often in quiet partnership with the United States. The region around Okinotori lies between Taiwan and Guam - two linchpins of America’s Pacific strategy.

Submarine cables criss-cross the area, while U.S. naval assets depend on unimpeded access through these waters. Chinese mapping here could hint at intentions not just for surveillance, but for anti-submarine operations or cable interception. China alleges that Japan’s claim to an EEZ from Okinotori is an imperial relic dressed up in legal language. It has accused Tokyo of clinging to ‘sea-grabbing’ practices while denying similar claims by others. This line appeals to countries like Taiwan and South Korea, both of which have protested Japan’s interpretation of UNCLOS in the past.

The East China Sea, the South China Sea and the Philippine Sea are increasingly connected theatres in an Indo-Pacific defined today by confrontation rather than cooperation. If Japan cannot uphold its claims here, it risks losing influence elsewhere, particularly in the face of a Chinese government that blends power politics with legal reinterpretation.