Territorial Force

The Territorial Force (TF) was the volunteer reserve component of the British Army from 1908 to 1920, when it became the Territorial Army. The Territorial Force was formed by the Secretary of State for War, Richard Burdon Haldane, following the enactment of the Territorial and Reserve Forces Act 1907 (7 Edw.7, c.9), which combined and re-organised the old Volunteer Army with the remaining units of militia and Yeomanry. The TF was formed on 1 April 1908.

More information on the Wikipedia page.