Kriegsmarine Commander of Submarines (Befehlshaber der U-Boote) Karl Dönitz devised a plan to attack Scapa Flow by submarine within days of the outbreak of war. Its goal would be twofold: first, that displacing the Home Fleet from Scapa Flow would slacken the British North Sea blockade and grant Germany greater freedom to attack the Atlantic convoys; second, the blow would be a symbolic act of vengeance, striking at the same location where the German High Seas Fleet had surrendered and scuttled itself following Germany's defeat in the First World War. Dönitz hand-picked Kapitänleutnant Günther Prien for the task, scheduling the raid for the night of 13/14 October 1939, when the tides would be high and the night moonless.Dönitz was aided by high-quality photographs from a reconnaissance overflight by Siegfried Knemeyer, (who received his first Iron Cross for the mission), and which revealed the weaknesses of the defences and an abundance of targets. He directed Prien to enter Scapa Flow from its east via Kirk Sound, passing to the north of Lamb Holm, a small low-lying island between Burray and Mainland. Prien initially mistook the more southerly Skerry Sound for the chosen route and his sudden realisation that U-47 was heading for the shallow blocked passage forced him to order a rapid turn to the northeast. On the surface, and illuminated by a bright display of the aurora borealis, the submarine threaded between the sunken blockships Seriano and Numidian, grounding itself temporarily on a cable strung from Seriano. It was briefly caught in the headlights of a taxi onshore, but the driver raised no alarm. On entering the harbour proper at 00:27 on 14 October, Prien entered a triumphant Wir sind in Scapa Flow!!! in the log and set a south-westerly course for several kilometres before reversing direction. To his surprise, the anchorage appeared to be almost empty; unknown to him, Forbes' order to disperse the fleet had removed some of the biggest targets. U-47 had been heading directly towards four warships, including the newly commissioned light cruiser Belfast, anchored off Flotta and Hoy 4 nautical miles (8 km, 5 mi) distant, but Prien gave no indication that he had seen them.On the reverse course, a lookout on the bridge spotted Royal Oak lying approximately 4,400 yards (4,000 m) to the north, correctly identifying her as a battleship of the Revenge class. Mostly hidden behind her was a second ship, only the bow of which was visible to U-47. Prien mistook her to be a battlecruiser of the Renown class, German intelligence later labelling her Repulse. She was in fact the World War I seaplane tender Pegasus.At 00:58 U-47 fired a salvo of three torpedoes from its bow tubes, a fourth lodging in its tube. Two failed to find a target, but a single torpedo struck the bow of Royal Oak at 01:04, shaking the ship and waking the crew. There was little visible damage; the starboard anchor chain was severed, clattering noisily down through its slips. Initially, it was suspected that there had been an explosion in the ship's forward inflammable store, used to store materials such as kerosene. Mindful of the unexplained explosion that had destroyed HMS Vanguard at Scapa Flow in 1917, an announcement was made over Royal Oak's tannoy system to check the magazine temperatures, but many sailors returned to their hammocks, unaware that the ship was under attack.Prien turned his submarine and attempted another shot via his stern tube, but this too missed. Reloading his bow tubes, he doubled back and fired a salvo of three torpedoes, all at Royal Oak, This time he was successful: at 01:16 all three struck the battleship in quick succession amidships and detonated. The explosions blew a hole in the armoured deck, destroying the Stokers', Boys' and Marines' messes and causing a loss of electrical power. Cordite from a magazine ignited and the ensuing fireball passed rapidly through the ship's internal spaces. Royal Oak quickly listed some 15°, suffic

Question: What is one flammable liquid stored in the ship?
Answer: kerosene