The Chinese military has laid powerful acoustic devices on the seabed near Guam to monitor U.S. submarine traffic.

The technologically advanced sensors are said to have a range of about 1,000 km — about 620 miles. China says that, officially, the sensors were put in place to study earthquakes, typhoons and whales.

But U.S. military experts say the listening devices are also capable of tracking submarines and intercepting communications between subs and command bases.

The devices have been in operation since 2016, but the Chinese Academy of Sciences only released information about the acoustic devices this month.

Guam is home to the United States’ biggest military base in the Western Pacific and it is also an important resupply and maintenance  center for the submarines of other US naval forces in the Pacific region. [source]