Over-the-horizon hiding is a simple tactic used by gray zone vessels to evade detection or public exposure. Ships can conceal their presence by relocating their vessels just beyond the earth's curvature—typically about 12-24 nautical miles away, depending on weather conditions and the elevation of the observing sensor. 

Hiding can also shield a vessel from being picked up by most basic radar systems. When coupled with the "going dark" tactic of deactivating a vessel's Automatic Identification System (AIS) broadcast, it becomes hard to detect.

Example: Starting on March 8th, 2023, a flotilla of Chinese maritime militia and coast guard ships that had been swarming the Philippines' Thitu Island outpost began to scatter. 

Many of these ships ended up loitering with AIS disabled in the area west of the nearby Chinese outpost at Subi Reef. 

However, by March 14th, dozens of Chinese vessels had returned to the reefs around Thitu Island and re-enabled their AIS transponders. 

The most likely explanation for this peculiar behavior is that the militia ships wanted to avoid being caught on camera. The Philippine government had at the time just launched its new transparency initiative and had begun publishing photos of the vessel swarm off Thitu.

The maritime militia continued the practice of scattering its ships around Thitu Island until it moved most of them further south in the summer of 2023.

See the rest of the gray zone playbook here.