By Ha Er-rui | 2026-06-05

The recovery of a Chinese undersea monitoring device in a strategic Indonesian strait has renewed scrutiny of Beijing's drive to build a sensor network that analysts say could help China track submarines across critical Indo-Pacific chokepoints.

An Indonesian fisherman pulled the 3.7-meter-long, torpedo-shaped object from waters near the Lombok Strait in April, the Australian Broadcasting Corp. (ABC) reported. Its body bore simplified Chinese characters and the "CSIC" mark of the China Shipbuilding Industry Corp.

The ABC reported that maritime defense analyst HI Sutton identified the device as a Deep-Sea Real-Time Transmission Mooring System, fitted with sensors to gather data on its surroundings.

The find may be part of China's Transparent Ocean Program, a system often described as China's "Great Undersea Wall."

Mapping the deep

Chinese oceanographer Wu Lixin outlined the program in 2014, according to the ABC. He suggested creating a real-time, three-dimensional observation system to span the western Pacific, the Indian Ocean and the South China Sea. Chinese researchers call that vast area "two oceans and one sea."

Wu proposed an ambitious four-layer network, to be linked by an artificial intelligence platform called "Deep Blue Brain" to process the data.

In a 2020 update, Wu and colleagues said the program had made research breakthroughs. China by then had deployed more than 100 surface buoys and subsurface moorings across the "two oceans and one sea," he said.

Dual-use data

The systems have civilian scientific uses, but China's "military-civil fusion" policy could channel the data toward military applications, Ryan Martinson of the U.S. Naval War College told ABC News.

Wu's writings and speeches indicate "that this project is driven, at least in large part, by a desire to apply this knowledge of the dynamic ocean to naval operations, especially submarine and anti-submarine warfare," he said. Martinson noted the views were his own and not those of the U.S. government.

The program serves Beijing's interest in exploiting deep-sea resources, especially seabed minerals in international waters, he said.

Beijing views U.S. undersea warfare capabilities, especially submarines and their ability to detect Chinese ones, as a disadvantage it must close, said Jennifer Parker, an adjunct professor at the University of Western Australia and former Australian naval officer.

"China has been working on enhancing their undersea domain awareness: their ability to understand what's happening in the water column and also to detect submarines," she told the ABC.

Variables like water temperature and salinity "give you an indication of how effective your sonars might be and how far sound might travel," Parker said.

Beijing dismissed such concerns in April. "It is not unusual for marine research equipment to drift into the territorial waters of other countries due to malfunctions or other reasons," a Foreign Ministry spokesperson told the ABC.

Indo-Pacific chokepoints

The Lombok Strait, between the islands of Lombok and Bali, is deeper and wider than the Malacca Strait. It is one of the few routes deep enough for submarines to pass between Australian waters and the South China Sea without surfacing.

China has used dozens of research vessels and hundreds of sensors, under the cover of fishery research and mineral exploration, to map key waterways off Guam, Hawaii and the Philippines, and in the Malacca Strait, Reuters reported in March, citing security analysts and ship-tracking data.

The report characterized the effort as "mapping the ocean floor as it prepares for submarine warfare with the US."

The "first island chain" -- the arc stretching from Japan through Taiwan and the Philippines to the South China Sea -- is widely viewed as a key defensive line for the United States and its allies.

Reuters quoted Peter Leavy, president of the Australian Naval Institute, as saying China is "paranoid about being boxed into the First Island Chain" and clearly has "a desire to understand the maritime domain so they can break out."

Marcus Hellyer, head of research at Strategic Analysis Australia, told the ABC that China's surveillance effort began in waters near its coast under an "anti-access area denial strategy" aimed at detecting U.S. and allied submarines in a conflict over Taiwan. But as China has built a "blue-water navy," he said, it needs awareness of the undersea domain far from home.

Eroding submarine stealth

The People's Liberation Army is building an "invisible net" across the western Pacific through the Transparent Ocean Program -- a five-layer sensor architecture meant to challenge U.S. and allied submarines seeking to maneuver and hide, according to a Defense One analysis last year.

An upgraded sensor network would reduce the number of hiding places for allied submarines, the analysis said.

Still, U.S. Navy leaders say the American undersea edge holds. U.S. submarines are still a key asset for allies because they "can stay concealed and operate for long periods in highly contested waters," in the summarized opinion of Vice Adm. Richard Seif, commander of U.S. Navy submarine forces, according to Straight Arrow News in March.

The likely impact of China's efforts is a reduction of the U.S. stealth margin "in certain approaches and chokepoints," in Seif's opinion. China is unlikely to succeed in creating full transparency undersea, he said.