Dallas served in the Crimean War from 1853–56, seeing action at Alma, Balaclava, Inkerman and the Siege of Sevastopol. During the course of the war he purchased the rank of captain in September 1854, as well as serving as the "aide-de-camp" to General Garrett. He wrote an eyewitness account of the war, consisting of 127 letters. He was made a member of the Order of the Medjidie, 5th Class, by the Ottoman Empire in March 1858. He later purchased the rank of major in October 1862, before being promoted to the rank of lieutenant colonel in January 1868. He retired from active service in March 1875. Dallas died at Huddersfield in February 1888.