[12] Cockatrice joined her sister ships in the 4th Destroyer Flotilla of the Home Fleet based at Portsmouth.

[13][14] With the outbreak of the First World War in August 1914, the 4th Flotilla, including Cockatrice, joined the newly established Grand Fleet, based at Scapa Flow in Orkney.

[19][20] The 4th Flotilla, including Cockatrice, left the Grand Fleet and moved to the Humber in July 1916,[21][22][23] with the role of protecting British minesweepers and deterring German minelayers off the east coast of England.

[23][28] On 13 and 14 May 1918, Cockatrice, on patrol with sister ships Christopher and Ambuscade, attacked possible submarine contacts with depth charges with no apparent results.

[29][30] Cockatrice was still part of the 4th Destroyer Flotilla in August 1918,[31] but by the end of the war had joined the Northern Patrol Force based at Dundee.