Japan is enhancing its surveying capabilities in its vast exclusive economic zone (EEZ) by upgrading an unmanned deep-sea probe and building a new mother ship to carry submersibles.
The enhancements come as Japan’s powerful neighbor China expands the presence of research vessels in the region.
When asked for comment, Japan’s consulate-general in Hong Kong referred Newsweek to a Japanese coast guard document, which said one of its missions was to guard the EEZ against foreign vessels conducting research activities without Japan’s prior consent or agreement.
In its response to Newsweek, the Chinese Embassy in Washington, D.C., cited an earlier comment by the country’s Foreign Ministry, which questioned Japan’s claim of an EEZ around a reef and said China’s ships were exercising the freedom of the high seas.
What Is an EEZ?
The United Nations Convention on the Law of the Sea (UNCLOS), an international treaty establishing the legal framework for order in oceans and seas, defines the EEZ as a maritime area extending up to 230 miles from the coastline and lying beyond and adjacent to the territorial sea, which under the treaty extends no more than 13.8 miles from the coastline.
Japan’s EEZ covers about 1.56 million square miles, compared with its land area of about 146,718 square miles. Tokyo said the EEZ was “indispensable” to Japan, allowing it to “exclusively develop valuable marine energy and mineral resources and exploit aquatic resources.”
According to UNCLOS, a coastal state has sovereign rights to “explore, exploit, conserve and manage” natural resources and jurisdiction over “marine scientific research” in the EEZ.
Collin Koh, a senior fellow at the Institute of Defense and Strategic Studies in Singapore, told Newsweek on Monday that “surveying activities” would be assumed to fall under the term marine scientific research. States seeking to conduct such activities must obtain prior permission from the relevant coastal state before carrying them out, he added.
What To Know
The Japanese government has decided to construct a new mother ship for carrying multiple manned and unmanned deep-sea probes, local media reported in July. Scheduled for completion in the 2030s, it would replace the current, aging mother ship, the Yokosuka—which was built more than three decades ago—to conduct “efficient surveys” of seabed resources.
In late July, the Japan Agency for Marine-Earth Science and Technology announced that its unmanned deep-sea probe, the Urashima, reached a depth of 26,246 feet during a recent trial in the Izu-Ogasawara Trench, which lies south of Japan in the western Pacific. The probe has been upgraded for deeper dives, enabling it to reach the deepest parts of Japan’s EEZ.
Japanese media noted that half of Japan’s EEZ has a depth of more than 13,123 feet, with many areas exceeding 19,685 feet. Hence, deep-sea exploration is essential for mining rare earths.
Interest in rare earths—comprising 15 lanthanides and scandium and yttrium, which are critical for modern technologies, such as artificial intelligence—is rising amid trade disputes between the U.S. and China.
China holds the world’s largest rare earth reserves at 44 million metric tons and produces 70 percent of the global supply.
China’s Challenge
While Japan is overcoming technological difficulties in developing natural resources in its EEZ, China poses a challenge for Tokyo in protecting its economic waters across the western Pacific. As of Tuesday, three Chinese oceanographic research ships had been detected conducting research activities in the EEZ without Japan’s consent since January.
Regarding Chinese research activities in Japan’s EEZ, Koh said the same set of marine scientific research data would be useful not only for advancing scientific knowledge and commercial applications—such as minerals—but also for military operations.
In areas known to contain seabed resources, these activities could be intended to prospect marine economic data that supports follow-on extractive operations, the analyst said.
For military applications, the gathered data could be used to create “undersea domain awareness” for planning submarine and anti-submarine warfare operations, he added.
Japan is a key United States security ally in restricting China’s military activities in the event of war in the western Pacific. It forms part of the first island chain—along with Taiwan and the Philippines—a north-south defensive line under a U.S. maritime containment strategy.
While Japan operates one of Asia’s—and the world’s—most advanced and best resourced maritime forces, the Maritime Self-Defense Force and the coast guard, it faces a challenge in the type of response it can make to unauthorized foreign activities in the EEZ, according to Koh.
“Besides keeping tabs on and issuing audio and visual challenge, Japan’s maritime forces couldn’t possibly ‘expel’ the transgressing foreign vessel in a forceful manner without potentially triggering a diplomatic incident or worse, an escalatory armed clash,” he said.
Last year, Hidden Reach, an initiative of the Center for Strategic and International Studies, issued a report identifying a total of 64 Chinese research and survey vessels active between 2020 and 2023, making it the largest fleet of civilian research vessels in the world.
Many of these vessels are operated by state-affiliated organizations with close ties to the Chinese military, while some have surveyed foreign EEZs without prior approval, the report said, warning that “the line between its civilian and military research is heavily blurred.”
What People Are Saying
Collin Koh, a senior fellow at the Institute of Defense and Strategic Studies, told Newsweek: “But there’s a gray area here that’s yet to be resolved: what about such oceanographic research and hydrographic survey activities carried out by military actors? This was a bugbear most prominently highlighted in the case of the U.S. naval surveillance activities in Chinese EEZ in particular.”
A 2025 Japanese coast guard document said: “In accordance with international law and domestic law, the [Japanese coast guard] conducts day-and-night surveillance and vigilance against foreign official vessels, oceanographic research vessels as well as illegal fishing by foreign fishing vessels.”
What Happens Next
China is likely to continue sending research ships into Japan’s EEZ despite Tokyo’s protests. It remains to be seen how the Japanese coast guard will enhance its monitoring of the country’s economic waters, including through cooperation with the Maritime Self-Defense Force.
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