William Creagh O'Brien was appointed Ensign with the 40th Foot on 19 Nov 1841, posted to India on 28 Feb 1842 for the Gwalior Campaign and at the Battle of Maharajpoor 29 Dec 1843, carrying the King's Colour, appointed Lieutenant with the 40th Foot on 26 June 1844, then exchanging to the 73rd Regiment as Lieutenant in 1846, promoted to Captain on 21 Dec 1852, posted to India in suppression of the Indian Mutiny, thereafter promoted to Major on 10 June 1862 and Lieut.-Col. on 1 Apr 1866, retiring on 14 Aug 1873.