The Royal Australian Navy's (RAN) Submarine Service began when Australia took delivery of two British built E Class submarines, AE1 and AE2 in May 1914. Following the declaration of World War I in August 1914, the first task of the RAN was to seize or neutralise German territories in the Pacific, stretching from the Caroline and Marshall Islands in the north, to New Britain and German New Guinea in the south. Both AE1 and AE2 formed part of the force sent to secure these possessions which carried a volunteer group known as the Australian Naval and Military Expeditionary Force, consisting of a battalion of 500 naval reservists and a battalion of 1000 infantry.
The force arrived at Rabual on the 11th of September. Two parties of Naval Reservists were landed, with orders to capture the enemy's two wireless stations there. Following an extended battle the overwhelmed German defenders agreed to an unconditional surrender. Rabual was secured the following day. Within a few weeks most of the German territories in the area, including Bougainville and the Admiralty Islands, had been occupied without further opposition.
The success of this operation was marred by the disappearance of AE1 on September 14, while patrolling the narrow St George's Strait between New Britain and New Ireland - the first RAN unit lost in wartime. No trace of the submarine or its 35 crew has ever been found.
With the demise of the German forces in the Pacific, AE2 was offered to the Admiralty for service in the European theatre, and she was towed to the Mediterranean by the transport Berrima which led the second Australian Imperial Force (AIF) convoy consisting of 17 transports. On arrival, AE2 was attached to the British fleet unit engaged in the Dardanelles campaign which included the landings at Gallipoli.