During the Second World War, he fought in the Battle of France, and was evacuated from Dunkirk. He commanded 2nd Battalion The Manchester Regiment during the Battle of Kohima fought on the Burma/India border from April to June 1944, despite being wounded on 24 April. King-Clark was promoted captain in 1942 and major in 1947 (although he was already acting in that rank). He wrote two books from his diaries of those times, "The Battle for Kohima", and "Forward From Kohima".