"Warrior" was ordered as part of the 1903–04 naval construction programme as the first of four armoured cruisers. She was laid down on 5 November 1903 at Pembroke Dockyard, launched on 25 November 1905 and completed on 12 December 1906. On completion, "Warrior" was assigned to the 5th Cruiser Squadron in the Channel Fleet until 1909, when she was transferred to the 2nd Cruiser Squadron. On 15 September 1909 one of "Warrior"s boiler tubes failed during firing practice, and she was repaired at Devonport Dockyard. In 1913 the ship was transferred to the 1st Cruiser Squadron of the Mediterranean Fleet. She was involved in the pursuit of the German battlecruiser "Goeben" and light cruiser "Breslau" at the outbreak of World War I, but was ordered not to engage them. "Warrior" participated in the Allied sweep which led to the sinking of the Austro-Hungarian light cruiser during the Battle of Antivari in August 1914. A few days later she was ordered to Suez to defend the Suez Canal against any Turkish attack and remained there until 6 November when she was ordered to Gibraltar to join a squadron of French and British ship to search for German warships still at sea off the African coast. This was cancelled on 19 November after the location of the German East Asia Squadron was revealed by survivors of the Battle of Coronel.