Ever since fighting ended in the Korean War nearly seven decades ago, Baengnyeong has been a key location for Seoul to spy on North Korea. Yet now the island is on China’s radar.

China spooked South Korea in December by sending a warship past a self-imposed boundary near the island to probe the limits of the country’s claims in the Yellow Sea. The move, described as rare by South Korean lawmakers, comes as China’s military bolsters its presence in the disputed waters.

Roughly 5,000 residents on Baengnyeong have also become wary of an influx of Chinese fishing boats near the island, which sits in a strategic location perpendicular to the Bohai Strait — the main waterway providing access to Beijing. In years past the island’s quartzite beach — one of a handful of natural runways in the world — was used for sorties in the Korean War.