[8] He stayed in South Africa throughout the war, which ended with the Peace of Vereeniging on 31 May 1902, and returned home on the SS Saxon which arrived at Southampton in late October 1902.
[12] At the outbreak of the First World War in July 1914, Montgomery was promoted once more to temporary lieutenant colonel[13] and appointed a general staff officer grade 2 (GSO2) of the 4th Division of the British Expeditionary Force (BEF), which landed in France in August.
Towards the end of the following month the division was temporarily commanded by Major-General Henry Rawlinson, "who formed a high opinion of Montgomery's abilities and thereafter retained him in his personal entourage".
It was a role for which, according to General Sir Douglas Haig, commander-in-chief (C-in-C) of the BEF from December 1915 onwards, from the planning for the Battle of the Somme in 1916 he carried out with "great ability and success".
[20] He was effectively deputy commander of the Fourth Army (deputising for Rawlinson) in the final months of the war and played an important role in the success of the Battle of Amiens.
[23] The medal's citation reads: The President of the United States of America, authorized by Act of Congress, July 9, 1918, takes pleasure in presenting the Army Distinguished Service Medal to Major General Archibald A. Montgomery, Royal British Army, for exceptionally meritorious and distinguished service in a position of great responsibility to the Government of the United States, during World War I.
[34] Despite this, according to Williamson and Millett, he was a great obstacle to innovation of mechanized forces and suppressed the analysis of the British Army's performance in the First World War initiated by his predecessor, Lord Milne.
[45] During the Second World War the Air Ministry attempted to build an airfield at Great Steeping in Lincolnshire that would have extended into Sir Archibald's wife's traditional family estate, necessitating the demolition of the magnificent mansion of Gunby Hall.
He personally appealed to King George VI and the Air Ministry relented, redrawing the plans that resulted in the resiting of the new RAF Spilsby two miles further south.