I don't know if it's MK-48s or some other torpedo, but I remember reading about torpedos designed to sink surface ships that used proximity fuses, and they did NOT impact the hull, but would dive down beneath the hull, and explode underneath the ship. The sharp overpressure, and then the sudden vaccuum, would cause the "spine" of the hull to crack, effectively cutting the ship in two pieces.
Mark
Actually, you're right on. That's how a 48 takes on a skimmer. Against another sub, it goes for a skin hit. In either case the target is well and truly fornicated.
" but would dive down beneath the hull, and explode underneath the ship"
I have seen some photos of several sinkex's, one being a Spruance class DD sunk by a Mk-48. The anti-surface mode appears to be how you described, since in the photo sequence the ship is lifted out of the water about amidships, settles back in, then breaks in two. The torpedo "hit" literally breaks the ship's back, or in this case the keel. As to what happened during the CV America sinkex, well, that's classified, and will remain so for years if not decades.