From the start, the relationship between the regular army and the Territorials was an uneasy one, the prevailing pattern of suspicion and antagonism being set by the First World War.
The same legislation also took away from prewar Territorials the right to seek their discharge at the end of their peacetime term of enlistment, as many had done in 1914-15.
Cannons were fired across the nation's capitals to mark the centenary launch - TA100, a major campaign to acknowledge the contribution of Territorial soldiers since 1908.
Founded by War Secretary Richard Haldane on April 1 1908, Territorial Army soldiers first saw action in World War I.
Ultimately responsible to the War Office, the Territorials were administered locally by county associations.
Nor was there an obligation on Territorials to serve overseas in the event of war, leaving the TF as essentially a home defence force.