On 19 March 1915, "Prince of Wales" was ordered to the Dardanelles to participate in the Dardanelles Campaign. She departed Portland on 20 March 1915 and was assigned to the British 5th Squadron of the Allied Fleet off the Dardanelles, where she arrived on 29 March. "Prince of Wales" supported the landings of the 3rd Brigade, Australian Army, at Gaba Tepe and Anzac Cove on 25 April. Her time at the Dardanelles was destined to be short as the Anglo-French-Italian Naval Convention of 10 May required that the British furnish a squadron of four battleships to reinforce the Italian Navy against the Austro-Hungarian Navy after Italy declared war on Austria-Hungary. Admiral Paolo Thaon di Revel, the Italian naval chief of staff, believed that the threat from Austro-Hungarian submarines and naval mines in the narrow waters of the Adriatic was too serious for him to use the fleet in an active way. He therefore kept his most modern battleships, plus the British ones, at Taranto to blockade the Austro-Hungarians in the Adriatic Sea.