Sayre failed to join the American army aged sixteen, but with a falsified birth certificate succeeded in joining the Canadian army, being subsequently sent to Siberia with its Expeditionary Force. On his return, he read literature at Exeter College, Oxford, graduating BA in 1922, and briefly studied medicine at Heidelberg University in Germany.
Sayre was unable to join the American army at sixteen due to age, but he obtained a false birth certificate that allowed him to enlist in the Canadian army. As a result, he was dispatched to Siberia with the Canadian Expeditionary Force. After his return, he pursued higher education, studying literature at Oxford University and later briefly exploring medicine at Heidelberg University.