Continuing his military service into the interwar period, most of it being spent as a captain, Hayes volunteered for service in Russia during the Russian Civil War in 1919, serving alongside Brian Horrocks on the staff of the Anglo-Russian Brigade, based in Vladivostok, and for ten months found himself as a prisoner of war (POW) by the "Reds". Returning to England, and marrying Florence Lllyanne, daughter of Henri Sudreau, in 1924, Hayes was promoted to captain on 10 January 1926, and attended the Staff College, Camberley from 1927 to 1928. His fellow students included several future general officers, such as Oliver Leese, Angus Collier, Eric Dorman-Smith, Eric Nares, Evelyn Barker, Philip Christison, Colin Jardine, Wilfrid Lloyd, Oliver Edgcumbe, Robert Bridgeman, John Hawkesworth, John Whiteley, Alfred Curtis, Edmund Beard, William Bishop, Stanley Kirby, Ronald Penney, Stephen Irwin, Charles Norman, Reginald Savory, Christopher Woolner and Clement West. Shortly after graduating from Camberley, from 21 May 1929 Hayes was appointed as a General Staff Officer Grade 3 (GSO3) at the War Office. Relinquishing this appointment on 1 March 1931, he was then made a brigade major with the 13th Infantry Brigade.