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 failed to join the American military at sixteen because of age, but he used a fake birth certificate to join the Canadian army instead. As a consequence, he was sent to Siberia with the Canadian Expeditionary Force. Upon his return, he continued his education, studying literature at Oxford University and later examining medicine at Heidelberg University.