The 12,000-ton China Coast Guard (CCG) 5901, widely referred to as "The Monster", has mostly been running "dark"--not broadcasting its automatic information system (AIS)--since departing Sanya port at Hainan Island on November 14th. (This frequent practice violates the International Convention for the Safety of Life at Sea, of which China is a signatory.)

There have been three exceptions to the ship's dark operations over this period. It turned on its AIS last December 9th and 29th, and now most recently on January 7th.

These patrols specifically target Vietnam's oil and gas operations in Blocks 06-01, 05-03, 12-11 and 12W according to a March 2023 analysis by Reuters and the South China Sea Chronicle Initiative. Vietnam shadows these patrols with its much smaller fisheries surveillance fleet.

SeaLight analyst Gaute Friis recently described the CCG's gray-zone tactic of intrusive patrolling, and how its "dark" vessels will often switch on their AIS transmitters to send a pointed message to its neighbors:

China Coast Guard vessels regularly and visibly conduct intrusive patrols deep within the exclusive economic zones of neighboring countries, an activity meant to establish a continuous presence and gradually normalize Chinese jurisdiction over areas granted to its neighbors under international law.

... CCG cutters conducting intrusive patrols often ensure their presence is noticed by engaging in "strategic illumination"—that is, switching their automatic information system (AIS) transponders on as they arrive in the area they will patrol, even if they were previously AIS-dark.

CCG 5901's previous intrusive patrols through this area took place between 8 June and 5 July 2023, and by rotating with other CCG ships 5205, 5304 and 5403 helped ensure a near-constant PRC presence near Vanguard Bank.