The Territorial Force (renamed Territorial Army in 1920) is formed as a volunteer reserve component of the British Army.

The Territorial Force was a part-time volunteer component of the British Army, created in 1908 to augment British land forces without resorting to conscription. The new organisation consolidated the 19th-century Volunteer Force and yeomanry into a unified auxiliary, commanded by the War Office and administered by local county territorial associations. The Territorial Force was designed to reinforce the regular army in expeditionary operations abroad, but because of political opposition it was assigned to home defence. Members were liable for service anywhere in the UK and could not be compelled to serve overseas unless they volunteered to do so.

The Army Reserve is the active-duty volunteer reserve force of the British Army. It is separate from the Regular Reserve whose members are ex-Regular personnel who retain a statutory liability for service. Descended from the Territorial Force, the Army Reserve was known as the Territorial Army (TA) from 1921 to 1967 and again from 1979 to 2014, and the Territorial and Army Volunteer Reserve (TAVR) from 1967 to 1979.

The British Army is the principal land warfare force of the United Kingdom. As of 1 January 2025, the British Army comprises 73,847 regular full-time personnel, 4,127 Gurkhas, 25,742 volunteer reserve personnel and 4,697 "other personnel", for a total of 108,413.

April 1 is the 91st day of the year in the Gregorian calendar; 274 days remain until the end of the year.