PRC Submarines

China is building up its submarine fleet.

Senior Chinese officers have said the buildup is strictly defensive.

This statement about the build up, I believe, is completely true. If China wants to invade Taiwan, they will need to prevent the US fleet from coming to the rescue. So having submarines can deny the sea to the US Navy and will protect China from US carrier attacks. They do not need or want to attack sea born commerce, China is dependent upon it. However they can deny the US Navy the ability to support Taiwan, so the PRC sub build up can be said to be defensive, protect China from the US when it attacks Taiwan.