In 1939, with the threat of war growing, Munro decided to withdraw from college and enlist in the military. He reportedly told his sister he had chosen the Coast Guard because its primary mission was saving lives. Slightly built, Munro spent the week before his induction eating heavily to meet the Coast Guard's minimum weight standard. He spent most of his last night in Cle Elum with his friend Marion "Mike" Cooley, with whom, according to Munro's biographer, Gary Williams, he had been "almost inseparable" since childhood.