China has built a gigantic antenna of 3,700 square kilometres, or five times the size of the city of New York. It took thirteen years to build the antenna, which can emit extremely low-frequency radio waves.
Officially, the device is intended for civilian purposes, among other things to measure earthquakes. But the Chinese defence can also use the antenna, reports the South China Morning Post.
Dive boats can pick up the radio waves hundreds of meters below the surface of the water, so that it is no longer necessary to get above water.
The Chinese government is secretive about the precise location of the 3,700 square kilometres where the antenna stands. Probably it is located in the Huazhong region, in the centre of the country, where about 230 million people live.
The complex looks like a power plant from above. Critics are concerned about the effect of the antenna on public health. The radio waves could be carcinogenic.