So today i went to the National Museum of the Royal Navy in Portsmouth and had a guided tour on board the battlecruiser HMS Hood (1) i can tell you it is a visit to do if you ever go to Portsmouth.
(1) during the Battle of the Denmark Strait on May 24th 1941 she fired what many called a lucky shot which manged to hit and detonating Bismarck magazine which caused here to split in two, after the end of the Battle of the Denmark Strait she went into a 2 year overhaul which she had organically had been planned in 1939 but the outbreak of the war got in the way.
I too am glad that the Navy kept HMS Hood on as a Museum ship (and I too would echo the ops sentiment and recommend that you pay her a visit) I just wish (Having visited the USS Enterprise Museum) that they had done the same for HMS Ark Royal veteran of (to name but a few) 1st and 2nd Taranto, The convoy battles, Club runs as well as 1st and 3rd South China sea's etc - but one is better than none I suppose!
I think it's easy to see what doomed the Bismarck - HMS Norfolk maintaining radar contact throughout the night despite the adverse conditions allowed the Hood and KGV to intercept Bismarck at sun up in a position to cross the Bismarcks 'T' and for the initial part of the engagement outmatch her 18 guns to 4.
As for which shell hit the German BB well those big heavy fat slow 15" shells would have been coming down near vertically at those ranges and linking Hood to KGVs modern Fire control made sure that both ships straddled the Bismarck fairly quickly at long range .
I think it's likely that one of Hoods 15 shells hit either forward of Anton or between Anton and Bruno Turrets and penetrating the deck entered or detonating near, the powder magazine (bypassing the angled armor) which unlike the other modern treaty designs of the day was above the Shell room and horribly exposed to such shell fire and aircraft bombs.
It's worth noting that HMS Hood at Denmark Strait had exactly the same type of design (with less armor!) having never been upgraded (Her Turrets were later modernised to the Mk1n standard during her 'Deep Refit' which aside from increasing the gun elevation swapped the Shell and Powder Magazine around as had been done in the 3 Modernised Queens and the Renown).
This does mean that the Hood was susceptible to a similar type of 'plunging' hit at this sort of range and some ATL scenarios place Hood at an angle were she receives a similar hit instead.
However I think it came down to the Bismarck and a Heavy Cruiser vs 2 Battleships, 2 Heavy Cruisers and 6 destroyers (and that does not include the other vessels in the area) - so I think that it would be safe to assume that even if Hood had been destroyed by a lucky hit - Bismarck and Prinz Eugen would still have been badly outgunned and out numbered and their fate would not have changed.