After attending the School of Gunnery he entered the Staff College, Camberley in 1892, and passed out, newly promoted to major, to command a field battery in England.
However, in early 1901 he was promoted to lieutenant-colonel and offered command of the 1st Battalion of the newly formed Imperial Yeomanry, volunteer mounted infantry being raised for service in South Africa.
In July 1912 he was given command of the South Midland Division, part of the Territorial Force (TF), taking over from Major General Alexander Thorneycroft.
[12] He remained with them until July 1914, when he was transferred to succeed Major General William Pulteney in command of the 6th Division,[13] a Regular Army formation at that time based in Ireland.
[3] Keir had hardly been in command of the 6th Division for a month when the First World War began, and it was mobilised as part of the British Expeditionary Force (BEF) for service in Europe.
[14] In late May, Keir was promoted to temporary lieutenant general[15] appointed to take command of the newly formed VI Corps,[16] which took part in the Battle of Loos in September.
Keir had previously protested to General Sir Douglas Haig, commander-in-chief (C-in-C) of the BEF, and as a result had acquired the sobriquet in Third Army of "the Matador" – i.e. the man who could handle "the Bull".
[19][20] On return to England Keir was side-lined and without a command, and spent the remainder of the war fulminating about the role of privileged "cavalry generals" (such as Haig and Allenby), who he argued held a disproportionate number of senior posts in the BEF compared to infantrymen, gunners and engineers.