Richard Haldane, 1st Viscount Haldane in the context of Leslie Ward

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 (1908 to 1921), 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 force was created in 1908 by the Secretary of State for War, Richard Haldane, when the Territorial and Reserve Forces Act 1907 combined the previously civilian-administered Volunteer Force, with the mounted Yeomanry (at the same time the Militia was renamed the Special Reserve).

The Army Reserve is the 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 (1908 to 1921), 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 force was created in 1908 by the Secretary of State for War, Richard Haldane, when the Territorial and Reserve Forces Act 1907 combined the previously civilian-administered Volunteer Force, with the mounted Yeomanry (at the same time the Militia was renamed the Special Reserve).

The Territorial and Reserve Forces Act 1907 (7 Edw. 7. c. 9) was an act of the Parliament of the United Kingdom that reformed the auxiliary forces of the British Army by transferring existing Volunteer and Yeomanry units into a new Territorial Force (TF); and disbanding the Militia to form a new Special Reserve of the Regular Army. This reorganisation formed a major part of the Haldane Reforms, named after the creator of the act, Richard Haldane.

The lessons learned during the South African War of 1899-1902 had reinforced the idea that the Regular Army was not capable of fighting a prolonged full-scale war without significant assistance; almost all regular units in the United Kingdom had been deployed overseas within four months of the outbreak of hostilities. Furthermore, by the end of the first year of fighting, the Regular Reserve and the Militia Reserve had been entirely exhausted. (Regular reservists were members of the Regular Army who had retired from the active-duty portion of their service but remained available for the callout. The Militia Reserve was a pool of individuals within the Militia, who accepted an overseas service liability). There had been no thought before the war about the wider use of auxiliary forces overseas; in the event, volunteers had been used on an ad-hoc basis, and a new auxiliary arm (the Imperial Yeomanry) was formed to provide specialist troops, but it was clear that a more effective system was required in future. A number of attempts at reform under the Conservative government of 1901-1905 had failed to make any lasting changes to the system and left the auxiliary forces disorganised and demoralised.

The Special Reserve was established on 1 April 1908 with the function of maintaining a reservoir of manpower for the British Army and training replacement drafts in times of war. Its formation was part of the military reforms implemented by Richard Haldane, the Secretary of State for War, which also created the Territorial Force. Haldane originally intended that the Militia would provide the reserve, but opposition from its representatives forced him to abolish it and create the Special Reserve instead. Only 60 per cent of the Militia transferred into the new reserve, and it was consistently under strength, particularly in officers. Reservists enlisted for a six-year term of service, and had to undergo six months of basic training on recruitment and three to four weeks training annually.

The Special Reserve was organised into battalions, providing the third (and sometimes fourth) for each of the regular army's 64 two-battalion infantry regiments and a fifth and sixth for the five four-battalion infantry regiments. In addition to providing replacements to the regular army, the Special Reserve was deployed on home defence duties guarding the coast and key installations during the First World War. The routine nature of its duties meant that scant attention was paid to it in regimental histories. After the war, the Special Reserve was abolished and the Militia was resurrected in 1921 to take on its former role. No effort was made to restart recruitment, and in 1924 the new Militia's functions were absorbed into the Supplementary Reserve.