Captain William Elliot Cairnes (18 September 1862 – 19 April 1902) was an Irish officer of the British Army and military writer.
From the militia, he received a commission as a lieutenant in the 3rd Dragoon Guards on 14 May 1884 and was transferred to the South Staffordshire Regiment a week later, and again to the 2nd Battalion of the Royal Irish Fusiliers in July 1884.
In March 1897, he was appointed Adjutant of the 1st Volunteer Battalion of the Yorkshire Light Infantry.
He was Secretary to the 1902 Committee on Education and Training of Officers, and also to the Military Court of Inquiry into the Remount Department.
Cairnes was the author of a number of works on military subjects, mostly written as commentaries during the Second Boer War (some was published anonymously):[1]