1935 to 16 June 1936. In January 1937 he was sent to the Territory of Hawaii, where he served with the 7th Service Squadron at Schofield Barracks, the 50th Observation Squadron at Luke Field, and the 18th Wing at Hickam Field. While at Luke Field he was as a navigation and operations staff officer, and conducted a navigation school for officers in the Hawaiian Department. In late 1938 and early 1939 he was the operations officer and then the assistant operations officer of the 18th Wing. He returned to the United States in April 1939, and was assigned to the 97th Observation Squadron at Mitchel Field, New York. He was promoted to the substantive rank of captain on 4 September 1939, and attended the Air Corps Tactical School at Maxwell Field, Alabama from January to March 1940. He was assigned to the 22nd Observation Squadron at Brooks Field, Texas, where he conducted a training course for combat observers. He was promoted to major on 15 March 1941. World War II In November 1941, Lindsay joined the War Department General Staff. He was initially assigned to the Air War Plans Division as member, and later as the chief, of the African-Middle East Section. He was promoted to lieutenant colonel on 5 January 1942. When the War Department was reorganized on 16 March 1942, he became as a member of the Policy Division of the Strategy and Policy Group in the Operations Division, the Army's global command post. He was chief of the Policy Division from 5 July 1942 to 9 May 1943, with the rank of colonel from 22 July 1942. On 10 May 1943 Lindsay was assigned to the Joint War Plans Committee, an organ of the Joint Chiefs of Staff, serving as its chief from 1 July 1944 to 27 June 1945. In this role he was involved in the preparation of studies for used by the Joint Chiefs of Staff and the Combined Chiefs of Staff to determine the nature of operations that the Allies of World War II would carry out, and he served as the United States Army Air Forces representative on the Joint Staff Planners of the Joint Chiefs of Staff. He was promoted to brigadier general on 10 September 1944. For his service with the Joint Chiefs of Staff, he was awarded the Army Distinguished Service Medal. In August 1945, Lindsay became Assistant Chief