A Western Australian Department of Defence was formed in the 1890s before the Commonwealth took over the Defence function in 1901 following Federation.

The Department of Defence was instrumental in establishing West Australian Contingents to serve in the South African War (commonly referred to as the Boer War).

Notes on Contingents to the South African War:

• 1st Contingent: This Contingent was established as a company of infantry by the general order in the Government Gazette of 13/10/1899. It consisted of one Captain, three Lieutenants and 125 other ranks. The period of engagement was to be for one year and men between the ages of 20 and 30 were qualified for enlistment. The company was designated "The West Australian Permanent Infantry" and sailed from Albany on 07/11/1899 on the S.S. Medic;
• 2nd Contingent: This Contingent was established as a company of mounted infantry in the Government Gazette of 22/12/1899. It consisted of one Captain, three Subalterns and fifty other ranks, which was later increased to 100 other ranks. The period of engagement was to be one year and men between the ages of 20 and 34 were qualified for enlistment. The company was designated the "2nd West Australian Mounted Infantry Company" and sailed from Fremantle on 03/02/1900 on the S.S. Surrey;
• 3rd Contingent: This Contingent was established as a company of mounted infantry in the Government Gazette of 16/02/1900. Details of company strength were not given but the notice stated that the current establishment of the permanent force was to be increased by 125, all ranks rates of pay were as before, with the additional direction that troopers providing their own horse and saddle would be granted a sum of 15 pounds plus refund of rail freight. The company was to be known as the "Bushman's Contingent" and sailed from Fremantle on 13/03/1900 on the S.S. Maplemore. The embarkation return lists 7 officers and 109 other ranks;
• 4th Contingent: This Contingent was established as a company of mounted infantry in the Government Gazette of 16/03/1900. It consisted of seven officers and 125 other ranks. The company was designated the "4th West Australian Mounted Infantry" and was known as the Imperial Bushman's Corps. It sailed from Fremantle on 08/05/1900 on the S.S. Manhatten;
• 5th Contingent: There appears to be no proclamation date for the establishment of this Contingent. However, it was likely early January 1901 as rail warrants were issued to volunteers from mid January. A general order for the Defence Force was published in the Government Gazette of 08/02/1901, appointing Captain Darling to command the Contingent. It was designated the "5th West Australian Mounted Infantry" and consisted of thirteen officers and 200 other ranks. They sailed from Fremantle on 06/03/1901 on the S.S. Devon;
• 6th Contingent: There is no recorded proclamation date for the establishment of this Contingent, however there is a general order in the Government Gazette of 05/04/1901 appointing officers for duty with this Contingent in South Africa. The commanding officer was Captain J. Campbell, transferred from the 1st Contingent. It was designated the "6th West Australian Mounted Infantry" and comprised thirteen officers and 215 other ranks. The Contingent sailed from Fremantle on 10/04/1901 on the S.S. Ulstermore.