following day. Although Gibraltar was well away from the main battlefields of the war – Spain remained neutral and the Mediterranean was not contested as it was in the Second World War – it played an important role in the Allied fight against the German U-boat campaign. The naval base was heavily used by Allied warships for resupplying and repairs. The Bay of Gibraltar was also used as a forming-up point for Allied convoys, while German U-boats stalked the Strait looking for targets. On two occasions, Gibraltar's guns unsuccessfully fired on two U-boats travelling through the Strait. Anti-submarine warfare was in its infancy and it proved impossible to prevent U-boats operating through the Strait. Only two days before the end of the war, on 9 November 1918, SM UB-50 torpedoed and sank the British battleship HMS Britannia off Cape Trafalgar to the west of Gibraltar. The restoration of peace inevitably meant a reduction in military expenditure, but this was more than offset by a large increase in liner and cruise ship traffic to Gibraltar. British liners travelling to and from India and South Africa customarily stopped there, as did French, Italian and Greek liners travelling to and from America. Oil bunkering became a major industry alongside coaling. An airfield was established in 1933 on the isthmus linking Gibraltar to Spain. Civil society was reformed as well; in 1921 an Executive Council and an elected City Council were established to advise the governor, in the first step towards self-government of the territory. The outbreak of the Spanish Civil War in July 1936 presented Gibraltar with major security concerns, as it was initially on the front lines of the conflict. The ultimately successful rebellion led by General Francisco Franco broke out across the Strait in Morocco, and the Spanish Republican government sought on several occasions to regain control of the Nationalist-controlled area around Algeciras. Although Gibraltar was not directly affected by the fighting, the war caused significant disruption. An undetermined number of Spanish refugees, perhaps as many as 10,000 persons, fled to Gibraltar, resulting in severe overcrowding. A Non-Intervention Patrol was mounted by the Royal Navy, operating from Gibraltar, to prevent foreign military aid reaching the belligerents in Spain. In May 1937, one of the ships involved in the patrol, the destroyer HMS Hunter, hit a Nationalist mine and had to be towed back to Gibraltar with eight of her crew dead.