Sinking the carrier...
I can think of a couple of ways that the sub could sink the carrier.
1. It's an older sub, perhaps an S-boat--and her skipper got stuck with a load of Great War torpedoes. Some of them were still around, and tended to explode. I'm not sure if any were on subs, or just a few old destroyers destroyers. Sometimes, the explosion would be less powerful, as the warhead had deteriorated--but perhaps not, also...
2. The sub has a poor angle, but it's the best shot he'll get--and the fish all strike at an oblique angle--much better chance of detonation.
3. Sometimes, although not as often as hoped for, American torpedoes would detonate.
3/4 crew casualties is perhaps unlikely, often, a warship sunk by submarine torpedos lingers a bit. Still, the right hit could start a fire close to the magazines--one oopsie on damage control, and kaboom!
Barham and Royal Oak come to mind as sudden explosions, while Ark Royal, Yorktown, and Audacious are the first slow motion sinkings to come to mind--either way is quite possible. Of course, how many hits plays a role as well...
Dayton Kitchens said:
The sub skipper gets the Medal of Honor.
FDR hails it as the "first great victory on the road back".
And the U.S. doesn't bother with the Doolittle Raid.
Though how an American sub with those pitifull torpedoes they had early in the war manages to sink a Japanese carrier is beyond me.