The Investigation Branch was formed in 1919 by the amalgamation of the Special Intelligence Bureau (CA 746) and the Commonwealth Police Force [I] (CA 2919). The Branch was established to co-ordinate the
investigation staff of Commonwealth departments, to reduce
Commonwealth reliance on the State police forces for assistance with investigations and to become the channel forcommunicating with State Departments for assistance with investigations. 

In 1925 the function of guarding Commonwealth establishments was added, by the creation of the Peace Officer Guard. The Central Office of the Investigation Branch (CA 747) was located in Melbourne until 1927, when it moved to Canberra. A separate Victorian Office was then established, the Central Office of the Branch having previously served as the State Office for Victoria.  Its function was to co-ordinate the investigation staff of Commonwealth departments, to reduce Commonwealth reliance on the State police forces for assistance with investigations and to become the channel for communicating with State departments for assistance with investigations.

The Security Service (CA 660), established in 1941, assumed the following duties of the Investigation Branch on 17 March 1942: 

 . Internal Security, including co-operation with the armed forces 
   Intelligence Services
 . Immigration Investigations
 . Passport Investigations

In Victoria the Security Service, Victoria (CA 949) took over these duties from the Victorian Office of the Investigation Branch. The Committee of Review on the Civil Staffing of Wartime Activities stated that the Investigation Branch:

maintained liaison with Customs, Postal, Taxation investigations  relating to industrial disputes; acted as a point of reference for Government Departments not having an office in any particular State; provided a translation service for Government Departments; conducted enquiries for Australian Offices overseas and British Empire Offices in Australia, and to and from accredited Consular Representatives of foreign Governments in relation to their particular Nationals; investigated newspapers and other publications  in foreign languages; reported upon applicants for naturalisation in foreign languages; reported upon applicants for naturalisation and landing permits; dealt with Cabinet matters involving urgent or special action not otherwise provided for; attended to the recovery of indebtedness to the Commonwealth and handled Air Force and Naval allotment investigations. On occasions the Branch also conducted special investigations for the Commonwealth Prices Branch and the Rationing Commission.

The Report noted that, as at 15 June 1945, the Victorian office of the Branch had a permanent staff of 11 and a part-time staff of six. The pre-war strength was seven. 

The Peace Officer based in Victoria, on that date, totalled 720 males and 69 females.

The Security Service was disbanded on 15 December 1945 and its activities and records were absorbed by a Security Section created within the Investigation Branch. The control and registration of aliens passing to the Department of Immigration (CA 51). 

On 8 August 1946 the Investigation Branch was abolished and replaced by the Commonwealth Investigation Service (CA 650) (Commonwealth Gazette No. 145, 8 Aug. 1946). The Investigation Branch, Victoria became the Investigation Service, Victoria (CA 916).


References

Federal Guides 1936, 1943, 1944
Committee of Review-Civil Staffing of War-time Activities. 
"Report on Commonwealth Investigation Branch 25 Sept. 1945".
C.D. Coulthand-Clark "Australia's War-time Security Service"
Defence Force Journal No. 16 May/June 1979.
 

Historical agency address
by1936-by1944: 318 Post Office Place, Melbourne
by1944-      : Summit House, 163-167 Flinders Lane, Melbourne