When the First World War broke out, "Ocean" was assigned to the 8th Battle Squadron, Channel Fleet, which she joined on 14 August 1914. She was detached to Queenstown, Ireland on 21 August to serve as guard ship there and to support a cruiser squadron operating in that area. In September 1914, she was ordered to relieve her sister ship "Albion" on the Cape Verde-Canary Islands Station, but while en route was diverted, first to Madiera and then to the Azores. The threat of the German East Asia Squadron and the independent cruiser , both of which were still at large, forced the Admiralty to redirect "Ocean" again, to the East Indies Station, to support cruisers on convoy duty in the Middle East. She was joined by the protected cruiser .