From the Preface;

"This is the Final Edition of the List of Etonians who served in the Great War between 4 August 1914 and 28 June 1919, or in the Baltic or Russia during the next few months.The rule made is that no one is included whose name was not in the Navy,Army or Air Force Lists during some part of that period......".

From the American Libraries Internet Archive.
Joe

http://www.archive.org/details/listofetonianswh00eton