In World War Two, Dunlop was posted to the Middle East. There he developed a mobile surgical unit that could move around to treat wounded soldiers. He also served in Crete and Greece. He fought in the battle of Tobruk. In 1942, Dunlop was sent to Java in Indonesia to treat wounded allied soldiers. Three years later, he was captured by the Japanese and became a prisoner of war. Dunlop was sent to Thailand-Burma Railway (AKA the death railway) between Bangkok and Rangoon. His medical skills, compassion and incredible courage in standing up to the Japanese inspired his fellow Prisoners Of War to keep going.