The first cruiser laid down for the RAN was Sydney which was launched in August 1912. Photo #1 is a painting from 1914 showing the Sydney steaming of Sydney Heads)

Following the outbreak of war on 4 August 1914, Sydney operated in New Guinea and Pacific waters and in the brief campaign against the German Pacific possessions during which she carried out a series of punitive patrols. Highlights during this period included the capture of Rabaul on German New Guinea (9 to 11 September 1914) and the destruction of the Angaur Island Wireless Station on 26 September 1914.

In October 1914, Sydney and her sister ship Melbourne detached from the Flagship HMAS Australia, and returned to Australia to form part of the escort for the first ANZAC convoy which consisted of some 38 transports. The convoy’s escort comprised Sydney (I), Melbourne, HMS Minotaur and the Japanese cruiser Ibuki. The convoy sailed from Albany on 1 November 1914 and on the morning of 9 November 1914 was steaming some 50 miles east of the Cocos Islands.

At about 06:20 on 9 November, wireless telegraphy operators in several transports as well as in the escorting warships received signals in an unknown code followed by a query from the Cocos Island W/T station, 'What is that code'? It was in fact the German cruiser Emden under the command of Captain Karl von Müller, ordering her collier Buresk to join her at Point Refuge to coal. Shortly afterwards, the Cocos Island telegraphists signalled 'Strange warship approaching’ followed later by the same message prefixed by ‘S.O.S.’ - the international distress call.

As von Müller patiently awaited the return of his landing party, smoke was sighted on the horizon which was at first assumed to be the Buresk. Soon afterwards the masts of the approaching ship were recognised as those of a warship. There was no time to take the landed train back on board, and the Emden ran out of the narrow roadstead of Port Refuge to meet the enemy. At 09:15 the Sydney had simultaneously sighted the island and the Emden some seven or eight miles distant. At first Captain Glossop could not tell whether the ship sighted was Emden or the Königsberg, both of which were thought to be at large in the Indian Ocean at that time. 

The Emden hoisted top flags and opened fire on the enemy ship, whose exact identity was still unclear at the time. The Sydney returned the fire immediately, but initially scored no hits on the Emden. Numerous 10.5 cm shells from the German cruiser, on the other hand, found their target, but caused only minor damage due to the Sydney's superior armour - apart from one hit in the fire control system and a dud blast into an ammunition chamber. Aware of the superior range and penetration of his 15.2 cm shells, the commander of the Sydney subsequently increased the distance to the Emden, whereby the Australian cruiser did not have to fear that the Emden could escape his grasp because of her superior speed.

In the further course of the battle, the Sydney brought decisive hits to Emden: in addition to the destruction of the radio booth, the chimneys were shot up, the foremast with the combat observation post was felled and most of the guns were disabled. In addition, a hit in the steering gear meant that the cruiser could only steer with its two screws. Moreover, the personnel losses were quickly very high, so that Commander Karl von Müller decided to set up his wrecked ship on the coral reef of North Keeling Island after the last guns failed, in order to prevent it from sinking and thus give the survivors a better chance to get rescue. At 11.20 a.m. the Emden ran aground in front of the island at a right angle to the coastline. The Sydney now pursued the coal ship Buresk, which had meanwhile also approached, and caught up with it after a while. The German crew on board the prize therefore sank the ship. The Sydney took over the Germans and returned to Emden around 4 p.m. As several requests for signals regarding a surrender were not answered and the war ensign was still flying aloft, the Sydney continued shelling the wreck until the war ensign was lowered. This killed 7 men and wounded 13. Four sailors drowned trying to swim to shore.

The next day, the survivors of the German crew were rescued from the wreck or from North Keeling. After that, the Sydney ran to Direction Island. But the 50 men from the landing train, under the command of Kapitän Leutnant von Mücke, had escaped the night before in the old schooner Ayesha.

The Emden had to mourn 136 dead crew members after this battle. 197 sailors, including 65 wounded and the 16-man prize crew from the Buresk, were taken prisoner, including Commander Karl von Müller. There were four dead and twelve wounded on the Sydney. The damage sustained was comparatively minor.

Emden's wreck was quickly destroyed by wave action, and was broken up for scrap in the 1950s.