"Going dark" refers to the gray zone tactic of turning off a vessel's Automatic Information System (AIS) transponder to avoid detection. AIS is a signaling system used to identify a vessel's type, position, course, speed and other navigation safety information, and is required by the International Maritime Organization for larger non-military ships operating in international waters. Read our primer on the AIS system here.
 
Going Dark in the Recent Water Cannon Incident

In a recent incident that involved the blockade and water-cannoning of a small Philippine resupply vessel and its escorts, six of the blockading ships were from the China Coast Guard. Of these, only one ship (CCG 5402) remained AIS-visible during the entire engagement, while two other ships (CCG 4203 and CCG 3302) broadcast AIS only intermittently. 

We can observe these periods of AIS-darkness from the dotted lines in the schematic below. 

The three other China Coast Guard ships documented by the Philippine Coast Guard as having taken part in the blockade--CCG 5201, 5304 and 5305--remained AIS-dark throughout the entire encounter. 

CCG 5304 arrived at China's military base at nearby Mischief Reef on 15 July with its AIS illuminated, and then patrolled the area for just over two weeks before moving east of Second Thomas Shoal. It then went dark near Sabina Shoal four days before the resupply mission.

The graphic below illustrates how 5304 went dark on 1 August, while the dashed line represents the fact that it was not detected again until it reappeared to the northwest 8 days later, after the resupply when it was well on its way back to Hainan Island. The period when it was in contact with the 5 August resupply mission is entirely missing from its AIS broadcast record.

Meanwhile, CCG 5305 went dark on 30 July while still inbound to the Spratly Archipelago, nearly a week before the resupply mission. As of this writing nearly three weeks later the ship is still AIS-dark.

The last CCG ship involved in the 5 August blockade, number 5201, is a notoriously shadowy vessel which seldom turns on its AIS transmitter. Even when it does, it generally uses a bogus identification number (412000008) which it shares with dozens of other Chinese ships.

Though extreme weather conditions can hinder the transmission of AIS data, no such conditions were present on 5 August. These ships clearly either turned off their AIS transponders or switched from their stronger Class A transponders to weaker Class B signals to avoid detection and mask their activities. 

Dark operations and bright lasers

CCG ships frequently go dark when disrupting these Second Thomas Shoal resupply missions. On 6 February 2023, for example, CCG 5205 harassed the Phillippine Coast Guard ship BRP Malapascua while impeding its resupply escort mission using a bright green laser, or "dazzler".

As the Malapascua approached its rendezvous with the resupply boats near Sabina Shoal on the evening of 5 February, CCG 5205 headed into its path before going dark. It remained dark during the resupply on 6 February, when it was documented as the perpetrator in the laser incident.

Strategic illumination

Finally, some vessels play the dark operations tactic in reverse when they specifically want to be noticed. This is common in the oil and gas fields off Vietnam's southeastern coast. In these cases, we often see CCG ships turn on their transmitters while they patrol near Vanguard Bank, indicating that China is openly asserting its jurisdiction over these waters.

This example from July 2023 is typical. Below we see the world's largest coast guard ship, the 12,000-ton CCG 5901, illuminate its AIS on 3 July just before crossing into Vietnam's EEZ from the south. It then goes dark again on 6 July after completing its patrol, before moving off to the east.

See the rest of the playbook here.