At the outbreak of the Second World War he joined the 77th Division of the 2nd Welsh Brigade, Royal Field Artillery along with four other footballers: Billy James, Jackie Pritchard, Billy Baker and Bobby Tobin. Their unit was posted to the Far East, where they were captured by Japanese forces in Java in 1941 and spent the duration of the war in a prisoner-of-war camp before being released in September 1945. During his time in the camp, Curtis taught Japanese officers how to play football with a ball made out of paper in order to obtain food. The effects of his imprisonment led Curtis to lose nearly half his body weight and his son later remarked how Curtis' wife barely recognised him on his return home. Curtis later attributed his survival to the fitness obtained from his football career.