The Battle of Cocos was a naval engagement that took place in the Indian Ocean, marking the first significant encounter between Australian forces and the German Imperial Navy during World War I. The German light cruiser SMS Emden, under the command of Captain Karl von Müller, had achieved notoriety for raiding Allied shipping in the Indian Ocean, disrupting communication and trade. The ship's operations had struck fear into British and Commonwealth shipping lanes, prompting a response from the Australian Navy.

On November 9, 1914, HMAS Sydney, under the command of Captain John Glossop, located the unsuspecting Emden hiding near the Cocos (Keeling) Islands. The encounter commenced with the Sydney opening fire. Using superior speed and gunnery, HMAS Sydney systematically targeted Emden, which was ill-prepared for a confrontation of this scale. The battle lasted for approximately 30 minutes, resulting in severe damage to the Emden, including the destruction of its main armament, leading to its eventual sinking. The crew’s efforts to stop the fire were in vain, and Captain von Müller ordered the scuttling of the ship to prevent further loss of life.

The engagement solidified the reputation of the Royal Australian Navy and represented a crucial moment in the early stages of World War I, as Australia began to take a more active role in the conflict. The demise of Emden marked a shift in naval power dynamics in the region and lifted morale within Australian ranks. Survivors from the German cruiser were rescued by the British ship HMS Yarra, reinforcing the nature of naval warfare and the interconnected fate of ocean-going vessels during wartime.