Comment by credit_guy

In case of a war with China, the US aircraft carriers would operate quite far out in the sea, most likely many hundreds of miles away from the continent. Submarines could try to get at them, but again, the most likely US tactic would be to have the carriers constantly on the move. China has 48 old Type 33 diesel-electric submarines, with a top (submerged) speed of 13 knots, less than half the top speed of any US carrier. The only hope for such a submarine to catch a carrier strike group would be to lie in wait. But the ocean is very large, and such a strategy is probabilistically very unlikely to succeed. China also has 6 nuclear attack submarines. It is however quite likely that in the even of a war, they'd be the first to be targeted by the US Navy. Sinking ships (or submarines) goes both ways.