In accordance with the Territorial and Reserve Forces Act 1907 which brought the Territorial Force into being, the TF was intended to be a home defence force for service during wartime and members could not be compelled to serve outside the country.

However, on the outbreak of war on 4 August 1914, many members volunteered for Imperial Service. Therefore, TF units were split in August and September 1914 into 1st Line (liable for overseas service) and 2nd Line (home service for those unable or unwilling to serve overseas) units. Later, a 3rd Line was formed to act as a reserve, providing trained replacements for the 1st and 2nd Line regiments.

1/1st Buckinghamshire Battalion Territorial Force
4 August1914 Stationed at Aylesbury as part of the South Midland brigade of the South Midland Division then moved to Writtle near Chelmsford.
30 March1915 Mobilised for war and landed at Boulogne.
May 1915 The formation became the 145th Brigade of the 48th Division which engaged in various actions on the Western Front including;
1916 The Battle of Albert, The Battle of Bazentin Ridge, The Battle of Pozieres Ridge, The Battle of the Ancre Heights, The Battle of the Ancre.
1917 The German Retreat to the Hindenburg Line, The Battle of Langemarck, The Battle of Polygon Wood, The Battle of Broodseinde, The Battle of Poelcapelle.
November 1917 Deployed to Italy to stiffen Italian resistance to enemy attack after a recent disaster at Caporetto.
1918 The Division held the front line sector at the Montello and then moved west, to the Asiago sector and then engaged in fighting on the Asiago Plateau, The Battle of the Vittoria Veneto in Val d’Assa.
4 November1918 Ended the war near Trent, Austria.

2/1st Buckinghamshire Battalion Territorial Force
Sept 1914 Formed at Aylesbury.
June 1915 Moved to Northampton and joined the 184th Brigade of the 61st Division and then moved to Chelmsford.
Mar 1916 Moved to Salisbury Plain.
26 May1916 Mobilised for war and landed at Havre and engaged in various actions on the Western Front including;
1916 The Attack at Fromelles (unsuccessful diversionary tactic during the Battle of the Somme).
1917 The Operations on the Ancre, The German Retreat to the Hindenburg Line, The Battle of Langemark, The German counter attacks.
22 February1918 Disbanded at Germaine with remaining personnel transferred to the 25th Entrenching Battalion.

3/1st Buckinghamshire Battalion Territorial Force
April & May 1915 Formed at Oxford and Aylesbury and then moved to Weston-super-Mare.
8 April1916 Became the 4th (Reserve) and 1st Reserve Bucks. Battalions.
1 September1916 Moved to Ludgershall the 4th absorbed the 1st as part of the south Midland Reserve Brigade territorial Force, then moved to Cheltenham.
March 1917 Moved to Catterick and then Seaton Delaval, Northumberland and remained there until the end of the war.