 In 1903, following the Federation of Australia, this unit became part of the Commonwealth Military Forces and was subsumed into the 1st Australian Infantry Regiment.In 1912, a system of compulsory military service was introduced and the unit was renamed the 21st Infantry, and then later, in 1915, the 22nd Infantry.This scheme greatly expanded the army, however, when World War I began, due to the provisions of the "Defence Act (1903)" which precluded sending conscripts overseas to fight, it became necessary to raise an all volunteer force, separate to the home military force – the Citizens Forces – for service in the Middle East and Europe.