From my information the Bismarck was hit about 700 times. The 1st hit was the most crucial, a 16 inc shell from the much smaller 1920's built British battleship HMS Nelson (or was it Rodney, - anyway, Nelson class) penetrated and detonated in the midship sector, depriving the Bismarck from further advanced gunnery control. After that, the Bismarck got shot up totally, while as shooting back, hitting none of the British.
Ballard's examination of the wreck did not reveal why the Bismarck went down, but as he put it: it did not really matter, it would only have been a matter of time, ot rather, not IF, but WHEN.
Now, regarding the ack speculations, quite truly, the British Swordfishes were able to drop their torpedoes at the Bismarck and emerge from the flak barricade mostly unharmed. (BTW, the Swordfish was NOT a WWI plane, however a fabric covered biplane). Bismarck's problem with hitting the planes was noting unique, - an attack from so low altitude is hard to stop, for so many of the AA guns can not point at their target. I belive that the Americanes also had their share of hard times against incoming "Kates".
Now that is all different in AH. Damned ack toasts you on the deck at whatever speed and angle.....