Gerard A. Hayes-McCoy (1911-1975) was an Irish historian born in Galway. He attended University College Galway (U.C.G.) and served as auditor of the College's Literary and Debating Society in the 1931/1932 academic year. He edited The Irish Sword, the journal of the Military History Society of Ireland (1949-1972) and he became Professor of History at the National University of Ireland (UCG) in 1958. He wrote primarily on military history, but also about Galway City, ships, historical figures in fiction, Robert Louis Stevenson and he even created a cartoon strip for the Cork Examiner. His work on the Scots mercenary forces in Ireland (1565-1603) established him as "one of the leading Irish scholars of his generation." It was based on his PhD thesis which he completed at the University of Edinburgh in 1934 . Hayes-McCoy produced several more works on Irish military history, including a detailed examination of the tactics used during Elizabeth's Irish wars of 1593-1601.
Hayes-McCoy's papers are held at the James Hardiman Library, National University of Ireland, Galway.
- 1937: Scots Mercenary Forces in Ireland, 1565-1603, reprinted 1996
- 1942: Index to "The Compossicion Booke of Conought 1585"
- 1959: Sixteenth Century Irish Swords in the National Museum of Ireland '
- 1963: Historical Studies IV: papers read before the Fifth Irish Conference of Historians (editor)
- 1964: The Irish at War
- 1964: Ulster and Other Irish Maps, c. 1600.
- 1965: Captain Myles Walter Keogh, United States Army 1840-1876 (O'Donnell lecture)
- 1969: Irish Battles: a military history of Ireland, reprinted 1990
- 1979: A History of Irish Flags from Earliest Times (posthumous)
- The Red Coat and the Green
- Essays in Commemoration - 1798 (contributor)