HMS Royal Oak - Battleship Royal Sovereign Class
Constructed at Devonport, laid down 1914, completed 1916
Displacement Design 25,750, finally 29,150, fully loaded 35,000 tons
Measurements 186m, beam 26.5m increased to 30.5m with anti-torpedo blisters, draught 10m
Propulsion Originally designed to be coal-fired, this class was changed to oil-fired during construction 4 sets of Parsons steam turbines to 4 propellers Performance 40,000 SHP and 23 knots
Armour Main belt 10inLength, armour deck 1.75in, increased to 4in at refit, Turrets 11in, control top 10in. Armament 8 x 15in main armament in twin turrets; 8 x 6in secondary; 8 x 4in AA high/low angle; 2 pom-pom AA Mountings 8 x 40mm; 2 x 4-barrelled 0.5in AA machine guns
Refitted several times, HMS Royal Oak's last major refit was in 1934/35, when much of her equipment was updated and 900 tons of extra deck-armour was added. This reduced her buoyancy and stability and made her an even wetter ship. She also had a catapult for a spotter-plane, new gun direction and new radio equipment fitted. In 1937 she was reckoned to be the best-equipped Royal Sovereign class battleship. Even by 1939, however, her slow speed and obsolete design, made her no match for her German opposition.

Scapa Flow at the outbreak of World War II was still very lightly defended. In particular many of the blockships sunk in World War I to block the eastern approaches had been shifted by the tide, or had disintegrated due to the effects of sea and wind. There were large gaps between the blockships in Kirk Sound, through at least one of which a submarine could pass. More blockships had been procured and there were plans for further coastal defences, but by early October 1939 these had still not been put in place. The Germans noticed this by photo-reconnaissance and Commodore Donitz, in charge of the U-boat command, decided to attempt an attack on Scapa Flow. Lt. Gunther Prien and his U47 were selected to undertake the mission and left Wilhelmshaven on 8 October. Meanwhile, the German Navy despatched Gneisenau, Köln and nine destroyers to the North Sea to lure out the British Navy. They succeeded in drawing out several battleships, cruisers and destroyers from Rosyth and Scapa on 8th October. No contact was made and all units returned to port. However, the British battleships all went to Loch Ewe rather than Scapa. Thus the daring submarine mission was sabotaged by its own Navy before Prien even reached Scapa Flow. The mission was carefully timed to coincide with a new moon, when high water at Kirk Sound was about 23:30. The plan was to enter at slack water, before the ebb (west-going) tide had built up. The lighthouses at Roseness and Pentland Skerries were turned on at 22:00 on the 12th, no doubt due to shipping movements, but also allowing Prien to have an accurate position. The next night at about midnight, U47 crept into Kirk Sound, passed the most northerly blockship on the surface, snagged a cable, came free and was soon in Scapa Flow, unobserved despite the lights of a turning car and the noise of her diesel engines. On the night of 13 October 1939 it seems that there were in fact very few warships in Scapa Flow, apart from a few supply ships, auxiliaries and so on, but no modern capital ships or aircraft carriers. The old HMS Iron Duke was lying at Lyness and being used as headquarters. Most of these ships were moored at the western side of the Flow, near Lyness, except for the old battleship HMS Royal Oak and the old sea-plane carrier, Pegasus, which were moored near Scapa Bay, below Gaitnip. HMS Royal Oak, with her considerable anti-aircraft firepower was there as local air defence for Netherbutton radar station, shore-based AA not yet having being installed in quantity. Although there was no moon, the night was clear, starlight thus allowing Prien to see the two ships to the north. At about 01:00 and from about 3,000m he fired three shots, and one hit the HMS Royal Oak at the bow inflicting little apparent damage, but causing both anchor chains to run out. In fact the crew thought it was an internal explosion in a paint store. After re-loading, three more torpedoes were fired and a few minutes later the ship was rocked by three explosions. The HMS Royal Oak sank within 15 minutes with the loss of 833 crew out of a total of about 1,200 officers and men. That so many were saved was due partly to the prompt action of the crew of the drifter Daisy II, which was moored alongside, as well as the quick response of Pegasus in getting its boats off to aid in the rescue work. The calmness of the weather that night also helped greatly. The vast majority were rescued by the Daisy and Skipper Gatt was awarded the DSC for his part. Meanwhile U47 slipped away on the surface, this time taking the south side of Kirk Sound and within a short time she had stemmed the strongly running ebb tide and made good her escape. The next day an old steamer, the Lake Neuchatel was sunk in Kirk Sound, too late to save Royal Oak. Prien and his crew were given a tremendous welcome in Germany, Prien being invested personally by Hitler with the Knight's Cross of the Iron Cross, which became the traditional decoration for exceptional U-boat commanders. Meanwhile Donitz was made a Rear Admiral. A few days later the Luftwaffe carried out bombing raids and it was not until March 1940 that the Home Fleet returned to Scapa Flow, by now heavily defended by anti-aircraft and coastal batteries, as well as improved minefields, indicator loops and more blockships. Churchill himself had the magnanimity to admit that Prien and his crew had carried out "a magnificent feat of arms". Although the loss of HMS Royal Oak was tragic for those lost, it was a salutary lesson for the British Navy and was to result in Scapa Flow being made into a safe base for the Home Fleet. Much controversy raged at the time about the sinking of the HMS Royal Oak. This was finally resolved when local divers Eric Kemp and Davie Gorn, diving near the wreck, found the remains of the propellers and gearboxes of two torpedoes of the type used by German U-boats in 1939. One of these may be seen in Stromness Museum. However the remains of the other torpedoes fired have never turned up.