"Cardiff", the second ship of her name to serve in the Royal Navy, was ordered in March–April 1916 as part of the Repeat War Programme. The ship was laid down by Fairfield Shipbuilding and Engineering Company at their Govan shipyard on 22 July 1916. She was launched on 12 April 1917 and completed on 25 June 1917. She became flagship of the 6th Light Cruiser Squadron of the Grand Fleet the following month. "Cardiff" participated in the Second Battle of Heligoland Bight on 17 November 1917. This was a successful attempt by the British to intercept German minesweeping forces that were clearing British minefields in the North Sea. The 6th LCS screened the two light s of the 1st Cruiser Squadron during the battle together with the 1st Light Cruiser Squadron. The British lost the German minesweepers in the smoke screen laid by the four German light cruisers and pursued the latter ships for most of the battle, although they inflicted little damage in the poor visibility caused by the German smoke. "Cardiff" fired the most of any ship in her squadron, but did not hit any German ships. She was, however, hit four or five times herself, killing seven crewmen and wounding thirteen, but was only lightly damaged. Based at Scapa Flow and Rosyth during 1918, the ship spent the remainder of the war escorting convoys and training in the northern portion of the North Sea. By 21 November 1918 the war was over, and "Cardiff" had the honour of leading the German High Seas Fleet to the Firth of Forth to be interned.