Oh she was seaworthy, all right, but slow and well past her "sell-by" date. She was antiquated because the limitations of the Washington Naval Treaty prevented the construction of "state-of-the-art" big-gun capital ships: the Kriegsmarine tore up the Washington Treaty when Bismark and Deutschland etc. were built.
In fact, all capital, big-gun ships were past their sell-by date in 1939. But the "big-gun" admirals yearned for a classic surface fleet action, another Trafalgar as it were, just as they did in round one, 1914-1918.
The penny finally dropped for the British "big-gun" admirals when H.M.S. Prince of Wales and H.M.S. Repulse were sunk by Japanese aircraft in 1942; the U.S. navy still lined up its beautiful, magnificent battleships in "Battleship Alley", Pearl Harbor until December 1940, in preparation for the day when they too might have to have a surface "Schlagfest" with the Imperial Japanese fleet.
With the U.S. navy too, the penny also quickly and bloodily dropped about the the role of navy "wings" and at Midway neither fleet saw each other, the contest being determined by airpower.
My former neighbour told me that many of the Royal Oak ratings were "boy sailors": in the Royal Navy you could become a "boy sailor" at 15.
"Jack" Cornwell VC was only 16 when he died of wounds received at the Battle of Jutland, 1916: he was a gun-layer on the cruiser H.M.S. Chester with a rating of "Boy Sailor First Class". Jack Cornwell stayed at his post, a 5.5 inch gun, even though the rest of the crew had been slain and he had received mortal wounds in his chest from shell plinters.
http://en.wikipedia.org/wiki/John_Cornwell
Like the U.S.S. Arizona at Pearl Harbor, H.M.S. Royal Oak remains to this day a 29,000 ton tomb.