I'm intrigued to read this report at Foxtrot Alpha.
A few years ago a Chinese fisherman from Hainan Province caught something totally unique: a torpedo-like device that was about three feet long and metallic. He took pictures of the contraption and called the authorities, who swiftly came and took it away for examination. Now, the Chinese Government has confirmed it is an elaborate spying device.
China.org.cn reports that authorities know what this silver torpedo-like device was used for and disguised to look like:
It is now confirmed that the unmanned underwater machine, disguised to look like a torpedo, is an intelligence device capable of taking pictures with fiber-optic and satellite communication. It was secretly placed in the water by a foreign country to obtain information on the Chinese navy fleet’s operations at sea.
Experts worried that the acquired information may have been sent back and that there are many other similar devices that haven’t been detected in the water, which pose great hidden dangers to information security in the South China Sea.
There's more at the link, including pictures of the 'torpedo-like device'.
This is very interesting. Yulin Naval Base can reportedly accommodate up to 20 submarines. In the photograph below, one of the entrances to the submarine tunnels (ringed in red) can be seen above the stern of a Type 094 ballistic missile submarine moored alongside a nearby pier.
Over and above the submarines, the base is a regional power projection base for the Chinese Navy. As such, it's a very logical target for intelligence gathering by any and every other power in the region.
The thought of a 'swimming' intelligence drone, that could slowly and silently make its way towards (perhaps even into) the submarine tunnels to see what's going on there, and eavesdrop on the acoustic and other signatures of nearby vessels, is intriguing. I suspect it's been going on for a while - the images provided with the Foxtrot Alpha article showed what I consider to be older technology, nowhere near as miniaturized and up-to-date as I've seen in other marine intelligence applications.
I don't suppose we'll learn any more about what this thing was doing there, or who sent it; but I think anyone with two brain cells to rub together can make the appropriate deductions.