On the outbreak of the First World War in August 1914, she was assigned to the 1st Light Cruiser Squadron of the Grand Fleet. On 28 August 1914 she was present, but played no significant role, in the Battle of Heligoland Bight, Several months later, the Germans bombarded Scarborough, Hartlepool and Whitby on 16 December and the 1st LCS was escorting Vice-Admiral David Beatty's battlecruisers in response when it encountered a German light cruiser and a half-flotilla of torpedo boats. "Falmouth" was not in range to engage before the squadron turned away to follow the battlecruisers. On 28 December, the ship was transferred to the 3rd LCS and became the flagship of Rear-Admiral Trevylyan Napier, the squadron commander. During the Battle of Dogger Bank on 24 January 1915, the squadron escorted the Grand Fleet, but was not engaged. After the battle was over, the squadron escorted the battlecruisers on their way back to Cromarty, Scotland.