Caves, tunnels, tanks, silos, submarines - all confined space death traps. Ask Hitler, ask Saddam. Ask all the people that have died in warfare in one of those confined spaces.
The Chinese submarine cave would be a very nice way to knock out as many subs that could fit in there. You know darn well all the major intel agencies with eyes in the sky know the exact count at any given moment.
Unless China bought those Iranian inflatable decoy subs and are using them to distract from where the real subs are parked.
GBU-57A/B Massive Ordnance Penetrator (MOP)...
Save the torpedoes for the surface fleet...
Death traps? I hope so. China, as I understand it, has hundreds of miles of underground tunnels to move around nuclear missles.