On Monday December 11th, the day after this past weekend's contentious Philippine resupply mission to Second Thomas Shoal, an extraordinary 11 Chinese vessels were visible inside the shoal while dozens more clustered around its exterior. 

This highly unusual invasion of the shoal's interior appears to have been a calculated show of force by Beijing.

Generally, most of China's blockading force will return promptly to its nearby Mischief Reef base once the Philippine resupply boats and their escorts depart. This weekend, however, the vessel swarm remained for an additional 24 hours (until Monday afternoon) and 11 pushed inside before returning to Mischief.

It's quite rare to see PRC vessels enter the shoal's interior at all, but 11 is certainly the highest number we've yet observed at SeaLight. In fact, it may be unprecedented.

Imagery from Planet Labs taken at 0955 local time (0155 UTC) on Monday clearly shows the 11 vessels spread throughout the shoal. Two were rafted together near the northwest corner about 2 kilometers south of the Philippines' BRP Sierra Madre, the grounded ship which has been its Second Thomas Shoal outpost since 1999. None of the ships that entered the shoal were detectable broadcasting automatic information system (AIS) signals. 

Meanwhile there were 27 vessels that were detectable on AIS surrounding the shoal, including China Coast Guard 5402 and 26 Qiong Sansha Yu militia ships. 

Additional ships were visible outside the shoal without corresponding AIS signals, so the total number is likely augmented by other AIS-dark militia and China Coast Guard ships known to be in the area. These probably include the smaller CCG ships 21551, 21555 and 21556 that were seen tied up at Mischief Reef a week before:

Of course, CCG 21556 was the ship that water cannoned and collided with Philippine resupply boat Unaiza May 1 (carrying Armed Forces of the Philippines Chief of Staff Romeo Brawner and Western Command's Commander Vice Admiral Alberto Carlos) on Sunday:

The total number of PLA Navy, China Coast Guard and maritime militia ships noted by the Philippine Coast Guard on Sunday was 46, and most appeared to remain in the area until Monday afternoon.

This final aggression capped off a deeply concerning and escalatory weekend of very aggressive PRC behavior against Philippine vessels. This included the harassment and water cannoning of Bureau of Fisheries and Aquatic Resources boats carrying oil subsidies and food to fishermen at Scarborough Shoal; the water cannoning of three vessels and disabling of one during the routine Second Thomas Shoal resupply; and the harassment of the civilian Christmas Convoy, prompting its organizers to abandon their planned holiday visit to bring supplies to deployed military personnel at West Philippine Sea outposts.

China is escalating.