He later served in the Second Boer War in South Africa 1899–1900, and was promoted a brevet major on 29 November 1900. For his service during the war, he was appointed a Companion of the Distinguished Service Order (DSO) in the South Africa Honours list published on 26 June 1902. Following the end of the war that month Kenna returned to the United Kingdom in the "RMS Dunottar Castle", which arrived at Southampton in July 1902. He received the substantive rank of major on 7 September 1902, on his appointment to lead a Mounted infantry flying column in Somaliland. In September 1910 he retired with the rank of Colonel from the Regular Army but in April 1912 was appointed to command the Notts and Derby (Yeomanry) Mounted Brigade and on the outbreak of war was appointed Brigadier-General.