A Chinese Survey Vessel Spent 53 Hours Over the SEA-H2X and EAC-C2C Cables

At a Glance

• A Chinese research and survey vessel spent about 53 hours inside a 29 nautical mile box over the SEA-H2X and EAC-C2C cable routes between October 30 and November 1, sailing roughly 226 nautical miles at a steady 5 knots.
• The track shows 39 sharp turns and 12 short stops, which are back-and-forth survey lines with station-keeping rather than drifting.
• It was a repeat visit, following a loiter 3 to 6 nautical miles from the APG and SJC2 routes on October 24 to 26.
• Its AIS navigational status read under way using engine throughout, even when stopped, never the restricted manoeuvrability status survey vessels use with gear in the water.
• The vessel is owned by a Chinese deep-sea robotics institute whose parent institution has been on the U.S. Entity List since 2022.

Fifty-Three Hours Inside a Twenty-Nine Mile Box

From October 30 to November 1, a Chinese research and survey vessel spent approximately 53 hours inside a 29 nautical mile box over the SEA-H2X and EAC-C2C cable routes in the northern South China Sea.

It covered about 226 nautical miles at a median of 5 knots, with 39 course changes over 45 degrees and 12 short stops. That is a back-and-forth line pattern with station-keeping. It is not a vessel drifting, holding position, or waiting.

Partway through, the vessel went dark for about four hours on October 31 and resumed transmitting 13 nautical miles north of where it stopped.

EO imagery caught it on station on November 1 at 03:02 UTC, directly above the SEA-H2X route.

It returned to its home berth at Nansha, Guangzhou, on November 3.

It Had Been There Six Days Earlier

The loiter was not isolated.

On October 24 to 26, the same vessel held position 3 to 6 nautical miles from the APG and SJC2 routes, going dark for 5 hours and again for 9 hours and 19 minutes while barely moving.

Two visits to two separate cable corridors inside eight days, with dark periods inside both, is a sequence rather than a coincidence.

The AIS Status Does Not Match the Behavior

One detail separates this from ordinary survey work.

Across all 230 recorded positions, including the stops, the vessel’s AIS navigational status read under way using engine. It never used restricted manoeuvrability, which is the status survey vessels set when they have equipment deployed and cannot manoeuvre freely.

The vessel has signalled that condition before, just not through AIS status. Earlier this year it used the destination field instead, broadcasting “KEEP CLEAR OF ME 3NM” in May and “KEEP CLEAR OF ME 2NM” in July and August. Those are gear-in-water warnings.

During the October and November loiters, no such warning appeared. The vessel either had nothing in the water, or chose not to say so through the channel that would have recorded it.

It has also gone dark for 10 to 14 hours at a time around the Paracels and off Hainan since August.

Who Owns It

The vessel is a 117-meter research and survey vessel built in 2023, owned, operated, and managed by a Chinese institute whose fleet consists of this one hull. It is not sanctioned, but Windward rates it as high risk.

Its dimensions match the 117.2-meter survey ship that the Guangdong Institute of Intelligent Unmanned Systems ordered from CSSC’s Guangzhou Shipyard International in 2021, specified with DP2 station-keeping, multibeam sonar and more than 600 tonnes of scientific payload.

The Chinese Academy of Sciences’ Shenyang Institute of Automation established the institute in Nansha in 2019 as its Guangzhou deep-sea base, co-built with the Guangzhou municipal government. The two jointly develop 6,000-meter AUVs and 7,000-meter ROVs.

The Shenyang Institute of Automation has been on the U.S. Entity List since 2022 for supporting military applications.

So the vessel conducting the pattern belongs to an institute whose specialty is deep-sea robotics, backed by a parent institution restricted by the United States.

Which Cables, and Whose

The ownership of the four cables involved matters to the assessment.

SEA-H2X is co-owned by China Mobile, China Unicom and Converge ICT, and lands in China, the Philippines, Singapore and Thailand. A Chinese vessel surveying it is unremarkable on its face.

EAC-C2C is different. It is Telstra’s alone, and it lands in China, Japan, the Philippines, Singapore, South Korea and Taiwan. APG and SJC2, the subject of the earlier loiter, carry Taiwanese, Japanese, Korean and Southeast Asian traffic between them.

What Slow Straight Lines Over a Cable Usually Mean

Running slow, straight, overlapping lines across a corridor for two days is how cable routes are surveyed with hull-mounted multibeam sonar. The pattern in the track is the pattern that method produces.

What raises the question beyond route mapping is the owner.

The U.S.-China Economic and Security Review Commission reports that China is developing hibernating cable cutters that could be pre-placed on an adversary’s cables, and confirms a 4,000-meter cable cutter built by a state shipbuilding research centre. Pre-placement is not a route-data problem. It requires getting to the cable itself, which is what deep-sea ROVs and AUVs are built to do.

On November 2, Yomiuri named four Chinese vessels for stopping over Taiwan’s cables. This vessel is not among them.

What Can and Cannot Be Said

AIS cannot show what a vessel had in the water. No survey is confirmed, no equipment deployment is established, and nothing here demonstrates interference with any cable.

What the record does show is specific. A survey vessel owned by a deep-sea robotics institute returned twice in eight days to cable corridors carrying Taiwanese, Japanese, and Korean traffic, ran a survey-pattern track over two of them for 53 hours, went dark inside both loiters, and did not set the AIS status that would have marked the work as a survey.

Windward assesses that profile as consistent with mapping these routes. Confirming more than that would require evidence that AIS does not carry.

Written by Maya Romi, Senior Content Manager, Windward; analysis by Gilad Karo, Critical Infrastructure Desk Lead, MIOC.