 With the outbreak of World War II, the College was dispersed to various parts of England and Wales.His strenuous efforts to hold the College together during wartime took a heavy toll on Mawer's health, and on 22 July 1942 he collapsed and died suddenly on a train in Broxbourne while on his way to a meeting of a committee in London.Mawer married Lettice Mona Kathleen Heath on 8 July 1909.