Battle of Lovćen, which was instrumental in Montenegro being knocked out of the war early. On 23 May 1915, when Italy declared war on Austria-Hungary, the Austro-Hungarian navy left their harbors in Pola (today Pula, Croatia), Sebenico (today Šibenik, Croatia) and Cattaro (today Kotor, Montenegro) to bombard the eastern Italian coast between Venice and Barletta. Main targets were the cities of Ancona, Rimini, Vieste, Manfredonia, Barletta and bridges and railway tracks along the coast. Until 1917 the Austro-Hungarian fleet was as yet largely undamaged. The presence of three Allied navies in the Mediterranean made any measures of their co-ordination and common doctrine extraordinarily difficult. The Mediterranean was divided into eleven zones, of which the British naval authorities were responsible for four, the French for four, and the Italians for three. Differing command structures, national pride and the language barrier all contributed to a lack of cohesion in the application of Allied sea power, producing a situation in which German and Austro-Hungarian U-boat attacks on shipping flourished. Battle at Durazzo In December 1915 a k.u.k. Kriegsmarine cruiser squadron attempted to make a raid on the Serbian troops evacuating Albania. After sinking a French submarine and bombarding the town of Durazzo the squadron ran into a minefield, sinking one destroyer and damaging another. The next day the group ran into a squadron of British, French, and Italian cruisers and destroyers. The resulting battle left two Austro-Hungarian destroyers sunk and inflicted light damage upon another, while dealing only minor damage to the Allied cruisers and destroyers present. A three-power conference on 28 April 1917, at Corfu, discussed a more offensive strategy in the Adriatic, but the Italians were not prepared to consider any big ship operations, considering the size of the Austro-Hungarian fleet. The British and French seemed reluctant to move alone against the Austro-Hungarians, especially if it meant a full-scale battle. But the Austrians were not inactive either, and even as the Allied conference was in session they were planning an offensive operation against the Otranto Barrage. Battle of the Otranto Straits Throughout 1917 the Adriatic remained the key to the U-boat war on shipping in the Mediterranean. Cattaro, some 140 miles above the narrow Straits of Otranto, was the main U-boat base from which almost the entire threat to Mediterranean shipping came. The Otranto Barrage, constructed by the Allies with up to 120 naval drifters, used to deploy and patrol submarine