The sinking of the HMAS Sydney, and the loss of her 645 crew members, shocked Australians deeply. Lack of information and wartime censorship helped foster rumours about the ship's fate.

In 1999 the Joint Standing Committee on Foreign Affairs, Defence and Trade conducted a detailed inquiry into the loss of the Sydney. It found little evidence to support the most controversial theories. With the discovery of the wreck of the Sydney in March 2008, some remaining questions might finally be answered.

The National Archives research guide, The Sinking of the HMAS Sydney, provides a detailed survey of Commonwealth government records relating to Australia's single worst naval disaster. Some of these records are displayed below.

The HMAS Sydney was sunk on 19 November 1941 after a battle with the disguised German raider Kormoran. On 24 November, after a number of unsuccessful attempts to contact the ship, a wide sea and air search was organised. Other than two lifebelts and a Carley float, no trace of the Sydney was found. Two days later, survivors of the Kormoran provided the first definite account of the Sydney's fate. Further interrogation of the raider's crew enabled Australian authorities to piece together the details of the battle. With many rumours circulating, the Prime Minister confirmed on 1 December that the Sydney had been lost.

There were no survivors from the sinking of the Sydney. The only source of information about her battle with the Kormoran came from the 315 German crew members rescued after the crippled raider was scuttled. The prisoners were interrogated by Naval Intelligence officers before being transferred to a prisoner-of-war camp in Victoria. No written records relating to the battle surfaced until 1945, when the encoded notebook of the Kormoran's captain TA Detmers was confiscated after his attempted escape.

Hampered by a lack of detail and concerned about the impact of the Sydney's loss, the Australian government was reluctant to provide the public with full information about the sinking. This contributed to persistent rumours of a cover-up. Other unexplained events, such as the later recovery of a corpse, and a radio signal of unknown origin, have encouraged speculation.