Dugald just to add some bits and peices on the Force X sinkings. The steel hull 'aprons' added at the Repulse's refurbishment also contributed to the success of the Japanese torpedoes. The aprons left vulnerable points around the propeller shafts - which is where, inevitably, some torpedoes hit (ironic that this had shades of how the Bismark was initially disabled by one of the batty old 'string-and-cloth' Fairey Swordfish British torpodo airplanes) .
I believe that the steel hull protection on both ships also left the lower hull areas vulnerable should the ships list much... as happened in both cases. This allowed successive penetrations by the high quality Japenese torpedoes you described.
The designers may have assumed that the high calibre steel protection would have precluded torpedo penetration; therefore why should they have to allow for lower hull protection when the ships would never be listing? (hindsight for my later generations is such a wonderful thing isn't it
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The commander of the Prince of Wales was credited with suberb seamanship under attack 'Throwing it around like a destroyer'. He succeeded in avoiding initial waves of attacking torpodo aircraft (the planes also of high quality Japanese design). Then the dastardly Japanese thought "let's surround the bastard!". They attacked simultaneously from all points and that was that.
Something else was fortunate for our people and at the same time odd: British destroyers were able to come alongside and rescue the bulk of the sailors from the overturned/sinking great ships. It was odd in-that if Japanese airplanes had returned they would have brought about a horrendous massacre of the completely vulnerable evacuators and evacuees.
Another wee poser for you... what was the other connection in WW2 between the old British Fairey Swordfish aircraft and the high-tech Japanese torpedo aircraft? (and no, it wasn't that all their torpedoes were produced at Alexandria on the Clyde
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