The torpedo?
Mines.
If you look at WWI and WWII the number of ships sunk per mines laid is astonishingly high.
And since 1950, of the 19 USN ships destroyed or damaged, 14 of them were by mines.
Ask yourself these questions:
1) How much mine-clearing capacity does the PRC have?
2) How much mine-clearing experience do they have?
3) What happens when every PRC commercial and military port gets mined?