China’s naval buildup is a serious threat, although at present the threat is mostly towards Chinese submariners (Strategy Pages via Thinking Towards Ourselves).:

Chinese boats are either bad copies of Russian designs, or even worse attempts to build Chinese designs. But the Chinese know that just having submarine crews is not enough, you have to get these guys to sea, as much as possible. Under the old Soviet system, the sub crews spent most of their time living in barracks, and getting lectured in classrooms, or doing dry runs while their sub was dockside, motionless. When Soviet subs did go to sea, it was for a day, and then back to port and the barracks. By the end of the Cold War, the Russians and the Chinese were convinced that the Western approach (keep the boats at sea as much as possible) was ancient wisdom that still applied, and worked.
The Chinese submariners have to work for their higher pay. Keeping their creaky boats at sea means a lot more maintenance and repair work in port, and a lot more alertness and tension at sea. There are more accidents as these boats are pushed beyond what they were designed for.