During periods of total war, the Army Reserve is incorporated by the royal prerogative into Regular Service under one code of Military Law for the duration of hostilities or until de-activation is decided upon.

All militiamen over 19 could join the Militia Reserve, accepting the liability to serve overseas with the Regular Army in case of war if called on to do so.

However, once the decision was taken to send a corps-size field force to fight in the South African War, the system began to show a strain.

On 16 December, the first request was sent from South Africa for auxiliary troops, and a commitment was made to send a "considerable force of militia and picked yeomanry and volunteers".

[9] The first Volunteer unit to be sent out was a 1,300 man composite battalion group, composed of infantry recruited from across London units and a field battery from the Honourable Artillery Company,[10] the City Imperial Volunteers, which was raised in early January 1900; it was sent into combat after six weeks of training in South Africa, where Lord Roberts described it as "quite excellent", and was returned home in October.

Haldane designed it to provide a much larger second line for the six divisions of the Expeditionary Force which he was establishing as the centerpiece of the Regular Army.

The next day, General - later Field Marshal - Haig, who had been central to Haldane's reforms and was then commanding First Corps, recorded in his diary that Field Marshal Kitchener did 'not appreciate the progress made by the Territorial Force towards efficiency',[22] The subsequent day, the 6th, Kitchener took up his post as Secretary of State for War announcing that morning 'He could take no account of anything but regular soldiers'.

[26] initially TF units were either fed into regular brigades or used for secondary tasks, such as guarding lines of communication but, by the end of April 1915, six full Territorial divisions had been deployed into the fight.

[1] The (Regular) Expeditionary Force of six divisions had been rapidly sent to the Continent, where, facing overwhelming odds, they secured the left flank of the French Army.

[30] From 1916, as the war progressed, and casualties mounted, the distinctive character of territorial units was diluted by the inclusion of conscript and New Army drafts.

To avoid war, the British Prime Minister Neville Chamberlain met with German Chancellor Adolf Hitler in September and brokered the Munich Agreement.

[49][50] The total strength of the TA was to be 440,000: the field force of the Territorial Army was to rise from 130,000 to 340,000, organized in 26 divisions, while an additional 100,000 all ranks would form the anti-aircraft section.

[55][56] This resulted in 34,500 twenty-year-old militiamen being conscripted into the regular army, initially to be trained for six months before deployment to the forming second-line units.

[58] As a result, some TA divisions had made little progress by the time the Second World War began; others, who had started from a stronger position, were able to complete this work within a matter of weeks.

[71] Partially as a result of lessons from Narvik, the Territorial Army was ordered to form 10 elite Independent Companies, forerunners of the Commandos.

Thus, on 1 May 1961, the TA divisional headquarters were merged with regular army districts, which were matched with Civil Defence Regions to aid mobilisation for war.

With opposition from employers and individuals to such a large peacetime liability, the target of 15,000 volunteers proved over-ambitious and the force peaked at 4,262 in October 1963, then dropping to around 2,400 by 1968.

[88] This was followed by a large reduction and complete reorganisation, announced in the 1966 Defence White Paper and implemented from 1 April 1967, when the title Territorial and Army Volunteer Reserve (TAVR) was adopted.

[94] In the face of a considerable Parliamentary battle, and a public outcry led by the County Associations, the government agreed to retain an additional 28,000 men in 87 'lightly armed' infantry units and a few signals units in a category called TAVR III, designed for home defence, but, months later in January 1968, these were all earmarked to be disbanded, with 90 becoming eight-man "cadres".

In the Reserve Forces Act of 1982, the Territorial Army title was restored, and, in the following years, its size was again increased, together with new equipment and extra training, the target being 86,000 by 1990.

[98] In addition, a new organisation was established, the Home Service Force, with a separate target of 4,500, composed of older ex-regulars and territorials to guard key points.

[102] in the 1991 Gulf War 205 Scottish General Hospital was mobilised as a unit based in Riyadh, Saudi Arabia, and a number of TA staff officers and others volunteered and served during the conflict, either in supporting roles in Germany or within 1 (UK) Armoured Division in the Middle East.

Some 2,800 TA personnel volunteered for and deployed on Operation Resolute from 1995 to 1998, the UK's contribution to the NATO mission to enforce peace in the Former Yugoslavia.

[110][111] The Royal Yeomanry mobilised Regimental Headquarters (RHQ) and two sub-units to deliver the UK's Chemical, Radiological, Biological, and Nuclear counter-measures for Operation TELIC.

"[113] Approximately 1,200 members of the Army Reserve deployed annually on tours of duty in Iraq, Operation HERRICK in Afghanistan and elsewhere, normally on six-month-long roulements.

[112] In 2010, the government set up a commission, chaired by General Sir Nicholas Houghton, to review the state of the reserves and to design their future.

[118] Most of the recommendations of the commission were adopted in the White Paper July 2013 including the critical importance of providing operational and training opportunities for formed units and sub-units.

Module B covers training in Tactics, Leadership, Doctrine and Navigation, both in theory and in practice, with a focus on the section battle drills and the platoon combat estimate.

CBRN training is also added at this point, and Officer Cadets undergo a number of field exercises to test their military and leadership skills.

Based at the RMAS, this module consists primarily of a prolonged field exercise, followed by drill training in preparation for the passing out parade.