The Chinese like to do drills of one sort or another.

So here is another:

http://en.people.cn/n3/2017/0716/c90000-9242246.html

If the drill was in the Eastern Pacific, it would be in the littoral area of California. It is in the Western Pacific it is off the littoral shore of China.

What on earth do they do it for?

They do it to let the top hegemon know:

If you want to come and F_ _ K with us

we are here waiting for you.

And of course this is in the face of the Pentagon axiom:

NO MORE LAND WARS IN ASIA.