She was laid down at Devonport on January 15, 1914 and launched on November 17. She was commissioned on May 1, 1916 having cost almost £2.5 million. The other ships of her class were the Royal Sovereign, Resolution, Ramilies and Revenge. She was the 11th Royal Navy vessel to bear the royal Oak name, replacing a pre-dreadnought that had been scrapped in 1914. She fought in the Battle of Jutland, in line behind the HMS Iron Duke of John Jellicoe.
She was refitted from 1922 to 1924, the main changes being the removal of torpedo tubes and a general upgrading of her anti-aircraft defences. She was modified again in 1934 at a cost of £1 million, much of the money being spent on upgrading her hull armour and torpedo bulges. She was assigned to the Mediterranean for most of the inter-war period and was accidentally struck by an anti-aircraft shell on February 1937 off the coast of Spain. She returned to the Home Fleet in 1938 and was made the flagship of the Second Battleship Division. She was preparing for another 30 month tour in the Mediterranean when WW II began. She was assigned to Scapa Flow and took part in a fruitless search for the Gneisenau in October 1939, in heavy seas her poor top speed left her out of contact for much of the time.
She was the first of the three Royal Nay battleships sunk in WW II. On October 14, 1939 she was moored within the defences of Scapa Flow. U-boat U-47, commanded by GŁnther Prien, entered the anchorage through Kirk Sound at high tide, passing over the sunk 'block ships' with almost 1.5 m to spare. Most of the fleet was out to sea and the Royal Oak was the only capital ship present, U-47 attacked her twice. The first salvo, fired at 0104, did little damage but the second at 0122 of three torpedoes was successful. The Royal Oak, struck amidships, rolled onto her side and sank in around 15 minutes. Of the crew 833 died, most almost immediately, 375 survived. 386 crew were rescued by the tender Daisy 2. U-47 escaped the anchorage an hour before the nets were raised and returned to Germany safely.
Initially the British believd that sabotage was the cause of the sinking, when a submarine attack was realised the anchorage was sealed, hours too late. Despite having warned of the paucity of anti-submarine defences Admiral Sir Wilfred French, Admiral Commanding Orkney and Shetlands was blamed for the loss and forcibly retired. The eastern approaches to Scapa flow were sealed with extensive concrete walls, the Churchill Barriers, linking Lamb Holm, Glimp Holm, Burray and South Ronaldsay to Orkney. AA defences were also significantly strengthened.