At the beginning of the First World War, the ships of the "Canopus" class were mobilised for service with the 8th Battle Squadron. "Canopus" was quickly sent to the South America Station, where she patrolled for German commerce raiders. She was involved in the search for the German East Asia Squadron of Vice Admiral Maximilian von Spee. Too slow to follow Admiral Sir Christopher Cradock's cruisers, she missed the Battle of Coronel in November 1914, where Cradock was defeated. Moored at Port Stanley as a defensive battery, she fired the first shots of the Battle of the Falklands in December, which led Spee to break off the attack before being chased down and destroyed by Admiral Doveton Sturdee's battlecruisers.