However, experience in the First World War did show that it was possible for a shell to hit the hull below the armour belt if the target ship was rolling significantlly.
And don't forget the Lion was hit below the waterline at Dogger Bank, for example, due to the hull's high-speed waveform in such shallow water. Not the case here, of course.
But - once again - the charge on a slow moving torpedo compared to the kinetic energy and explosive force of (as Adrian pointed out) base-fused rounds of the period make the point mute. Apples are NOT oranges, and it is certainly possible that the Hood was sunk as the result of an underwater shell hit.
Here's a then-sceret report from the Prince of Wales after being dry-docked after the confrontation:
The damage sustained in PRINCE OF WALES in her recent action has now been examined by D.N.C's representative.
SECRET
Subject.. Unexploded Enemy Shell
From .. The Commanding Officer, H.M.S. PRINCE OF WALES
Date .. 8th June, 1941 No. 001.A/1
To .. THE COMMANDER IN CHIEF, HOME FLEET.
(Copies to The Secretary of the Admiralty.
The Commander-in-Chief, Rosyth
During the early morning action on May 24th a heavy hit was felt abreast the Starboard Diesel Room. It was found that the outer air space 184-196, the outer oil fuel tank 184-206, the inner air space 184-194, the starboard diesel tank 184-206 were fill to the crown with oil and water.
2. On Friday 6th June, on pumping out the dry dock a clean hole in the side about 15" diameter was found, a foot above the bilge keel at 187 starboard.
Holes were also found in the light plating forming the sides of the outer oil fuel tank 184-206.
Heavy marking was found on the protective bulkhead but there were no signs of explosion.
3. When the ship's bottom was visible it became apparent that there was no exit hole and a search was made for the shell.
TV - even Mythbusters (!) - is not necessarily the truth, Josse.
Andy