HMS Cardiff was a C-class light cruiser built for the Royal Navy during World War I. She was one of the five ships of the Ceres sub-class and spent most of her career as a flagship. Assigned to the Grand Fleet during the war, the ship participated in the Second Battle of Heligoland Bight in late 1917. Cardiff was briefly deployed to the Baltic in late 1918 supporting anti-Bolshevik forces during the British campaign in the Baltic during the Russian Civil War.

The Second Battle of Heligoland Bight, also the Action in the Helgoland Bight and the Zweite Seeschlacht bei Helgoland, was an inconclusive naval engagement fought between British and German squadrons on 17 November 1917 during the First World War.