Callwell "the Clausewitz of colonial warfare". Intelligence and Staff officer On 1 October 1887 Callwell was seconded for service as a Staff Captain in the Intelligence Branch at Army Headquarters. On 13 July 1891 he was appointed Deputy Assistant Adjutant-General, serving until September 1892, when he returned to the Royal Artillery as a captain. Callwell was seconded for service on the General Staff on 9 September 1893, and was later was appointed a brigade major in the Western District of the Royal Artillery, serving until September 1896, having received promotion to the rank of major on 25 March 1896. On the outbreak of the Greco-Turkish War in April 1897, Callwell was attached to the Greek army and spent a year in the Near East. In October 1899, when war was declared against the Boer Republics in South Africa, Callwell was appointed to the staff of Sir Redvers Buller, and was present throughout the operations which ended with the relief of Ladysmith on 28 February 1900. In September 1901 he received a mention in despatches from Earl Roberts, and was awarded the brevet rank of lieutenant-colonel (dated to 29 November 1900), and given command of a mobile column, with which he served in the Western Transvaal and in Cape Colony until the close of the war in June 1902. He left Cape Town for England the following month, and arrived in Southampton in August 1902. A year after his return to England, he was appointed a Deputy Assistant Quartermaster-General in the mobilization branch of the War Office on 6 October 1903, and by April 1904 was working in Intelligence once again. On 1 October 1904 he was appointed an Assistant Director of Military Operations, with the substantive rank of Colonel. In June 1907 Callwell was made a Companion of the Bath, at which time he was General Staff Officer, 1st Grade, at Army Headquarters. In October 1907 his appointment to the Staff came to an end and he was placed on half-pay. Having seen several of his contemporaries promoted to general officer rank over his head, Callwell eventually quit the army in June 1909, to devote himself to writing. First World War On the outbreak of the First World War in August 1914, Callwell was recalled to active service, being appointed Director of Military Operations at the War Office with the temporary rank of major-general. He carried out much important work