Depending upon where the hits are, the Kongo takes 4-6 to sink. The Yamato is 10 at a minimum, and I've had a time where I put 18 into it, and it did not slip beneath the waves. In that particularly frustrating patrol, my hits where down the length of the ship, over the course of a day. Concentrating on one area, especially the bow when they're moving, seems to help "pull" them under. The DD not coming and pouncing on you concerns me though. Can't have that...
