World War I: Off the Cocos (Keeling) Islands, the Australian light cruiser Sydney sank Emden, the last active German warship in the Indian Ocean, at the Battle of Cocos.

World War I or the First World War, also known as the Great War, was a global conflict between two coalitions: the Allies and the Central Powers. Main areas of conflict included Europe and the Middle East, as well as parts of Africa and the Asia-Pacific. There were important developments in weaponry including tanks, aircraft, artillery, machine guns, and chemical weapons. One of the deadliest conflicts in history, it resulted in an estimated 30 million military casualties, plus another 8 million civilian deaths from war-related causes and genocide. The movement of large numbers of people was a major factor in the deadly Spanish flu pandemic.

The Cocos (Keeling) Islands, officially the Territory of Cocos (Keeling) Islands, are an Australian external territory in the Indian Ocean, comprising a small archipelago approximately midway between Australia and Sri Lanka and relatively close to the Indonesian island of Sumatra. The territory's dual name reflects that the islands have historically been known as either the Cocos Islands or the Keeling Islands.

HMAS Sydney was a Chatham-class light cruiser of the Royal Australian Navy (RAN). Laid down in 1911 and launched in 1912, the cruiser was commissioned into the RAN in 1913.

SMS Emden was the second and final member of the Dresden class of light cruisers built for the German Kaiserliche Marine. Named for the town of Emden, she was laid down at the Kaiserliche Werft in Danzig in 1906. The hull was launched in May 1908, and completed in July 1909. She had one sister ship, Dresden. Like the preceding Königsberg-class cruisers, Emden was armed with ten 10.5 cm (4.1 in) guns and two torpedo tubes.