Analysis of satellite imagery from the past year shows that hundreds of Chinese militia vessels continue to operate in the Spratly Islands on a daily basis. The data confirms the massive scale of militia force in the Spratlys. It also shows a marked consistency in their movement and behavior patterns despite outcries from other claimants: militia continue to mass around Whitsun and Hughes reefs in Union Banks and maintain a persistent presence at other key features, such as Philippine-occupied Thitu Island.

This effort to track the militia’s movements builds upon a series of discoveries published in the November 2021 report Pulling Back the Curtain on China’s Maritime Militia, which features a comprehensive overview of the militia’s history, organizational structure, activities, government funding, and patterns of behavior.

The Analysis

AMTI reviewed satellite imagery from September 2021 through September 2022 at nine known militia hot spots in the Spratly Islands as well as six militia homeports in Hainan (Wenchang Qinglan; Danzhou Baimajiang, Sanya Yazhou) and Guangdong (Yangjiang Puyuzhou; Maoming Bohe; Taishan Shadi) and counted the number of vessels matching the description of Chinese maritime militia at each location throughout the year. Chinese fishing vessels operating as part of the two South China Sea militia fleets—Professional Maritime Militia Fishing Vessels and Spratly Backbone Fishing Vessels—are virtually all between 45 and 65 meters in length. When deployed to the Spratly Islands, this makes them easily distinguishable in 3-meter-resolution satellite imagery from both the smaller fishing ships of other claimants as well as larger law enforcement and military vessels. Distinguishing militia ships in Chinese ports, on the other hand, requires the use of higher resolution imagery from Maxar or Planet Lab’s SkySat constellation. At some ports, particularly the homeports of Professional Maritime Militia Fishing Vessels on Hainan, docking facilities for militia ships are separate from the rest of port traffic.

Seasonal Patterns

The data confirms that China’s militia in the South China Sea numbers in the hundreds of vessels. The total count of militia vessels deployed to the Spratly Islands and in port peaked at 400 in early July.

The data also shows at least one clear pattern in the militia’s seasonal behavior: most go home for the holidays. The number of militia deployed in the Spratly Islands dropped starkly in late December, falling from 128 to just 12, before shooting up again in mid-February to 170. The trend played out in reverse at militia ports, where total vessels went up from 100 in early December to over 200 in mid-January, and could be seen filling up the harbors in satellite imagery:

It is unsurprising that Spratly Backbone Fishing Vessels, the segment of the militia recruited from among the ranks of China’s commercial fishing vessels, take an extended winter vacation, as they are only required to spend 280 days of the year in disputed waters to earn their subsidies. But the imagery and the data show that the professional militia operating out of Hainan stay in port for a similarly long period.

Hot Spots

Examination of the trends at individual features confirms that, by and large, the behavior of China’s militia in the past year has been consistent with patterns that emerged two years prior.

The largest masses of militia vessels deploy to Union Banks, with 100-150 vessels typically spread between unoccupied Whitsun Reef and the areas around China-occupied Hughes Reef. A smaller, but persistent, deployment of approximately 20 vessels on average can be found year-round just west of Thitu Island, the Philippines’ largest Spratly Island outpost. Significant numbers of militia can also be found at China’s three largest outposts in the Spratlys: Fiery Cross, Mischief, and Subi Reefs. The numbers of militia frequenting Scarborough Shoal and Second Thomas Shoal are much lower. At these two features, the better-trained and equipped Professional Maritime Militia Fishing Vessels, rather than the more numerous Spratly Backbone Fishing Vessels, operate in support of China Coast Guard patrols. These professional militia are more reliable and less likely to cause an unintended incident at these features, which see frequent tense interactions with Philippine military and civilian vessels.

It is also noteworthy that the average number of vessels at each feature remained relatively consistent throughout the year, with the one minor exception being a shift of vessels within Union Banks from Whitsun Reef in the fall to Hughes Reef in the spring. This differs from the previous year, when Philippine protests about the massing of vessels at Whitsun led most militia ships to vacate Union Banks entirely in the spring and return only in late summer.

Numbers Aren’t Everything

This data is necessarily incomplete. Collection was subject to the availability of clear satellite imagery, which differed at each location. Ship counts on days without imagery are estimates created by interpolation between the two nearest data points.

Vessels at Sabina Shoal, a reef that occasionally sees small numbers of militia, were not captured in the analysis.

These estimates likely capture the majority of, but not all, Chinese militia vessels in the South China Sea. Several known militia ports, including Zhanjiang and Jiangmen in Guangdong, were excluded from the analysis due to a lack of sufficient imagery or the absence of a clear separation of militia from other vessels within the ports. The Paracel Islands were also excluded: past observation has shown that the militia do not frequent them in large numbers, and that nearly all professional militia vessels that are officially registered to Woody Island’s Sansha City in reality operate out of ports on Hainan instead. And in the Spratly Islands, data collection was limited to a selection of features known to be frequented by militia and Chinese law enforcement: vessels at other locations, or in transit between features, were not captured.

This analysis’s period of observation ended in September, but recent imagery showing over 80 militia ships at Whitsun Reef suggests that the patterns observed will continue for the foreseeable future—and that more than 100 Chinese militia operating within Union Banks has become the new normal.