Attending the Staff College, Camberley from 1931 to 1932, alongside Brian Horrocks, Sidney Kirkman, Cameron Nicholson and Thomas Rees, Dowler also saw active service in the Second World War, initially in 1939 as Commanding Officer (CO) of the 1st Battalion, East Surrey Regiment and then as a General Staff Officer (GSO) with the 49th (West Riding) Infantry Division. In 1940 he was promoted to Brigadier and served on the General Staff of V Corps and, promoted on 1 October 1940 to colonel, subsequently commanded the 2nd Infantry Brigade. He was involved in the Narvik expedition in 1940, part of the Norwegian Campaign. In 1942 he was made General Officer Commanding (GOC) of the 38th (Welsh) Infantry Division and then Major-General in charge of Administration of Southern Command. He was put in charge of Administration for the Mediterranean Expeditionary Force (MEF) in 1944.