the de Havilland DH-4 observation airplane as its primary equipment from 1919 to 1928. The 1st Squadron was assigned as a component squadron of the new 9th Observation Group on 1 August 1922. It was assigned directly to the II Corps on 23 March 1923, as the 1st Observation Squadron, but remained attached to the 9th Observation Group. This command arrangement continued until 15 February 1929, when the 1st Observation Squadron was permanently assigned to the 9th Group. Its aircraft from 1928 to 1935 was primarily the Curtiss O-1B Falcon observation plane, but it also field tested and employed other Falcon variants (O-13, O-39, and Y1O-40 Raven) and several Douglas observation types, the Y1O-31, Y1O-35 and O-35. The 1st Observation Squadron's O-35s all participated in delivering the U.S. Mail in 1934 without loss. The Air Service became the U.S. Army Air Corps on 2 July 1926, and kept that title until reorganized as the United States Army Air Forces on 20 June 1941. In early 1935 the Air Corps was re-organized, with all combat groups being centrally controlled for the first time, under a new command organization called General Headquarters, Air Force. The role of observation as the primary function of the air arm had been de-emphasized in the creation of eight new Air Corps groups between 1927 and 1932. With the creation of General Headquarters Air Force (GHQAF) it was further de-emphasized when the 9th and its component squadrons were converted into a bombardment group and made a part of the 2nd Wing, responsible for the air defense of the East Coast of the United States. The 1st Observation Squadron became the 1st Bombardment Squadron on 1 March 1935, and was equipped with Keystone B-6 bombers. It converted to Martin B-10 bombers in 1936 and operated these until 1938, when it again re-equipped, with Douglas B-18 bombers. The designations of the squadron changed in the late 1930s as the role of bombardment became pre-eminent in the Air Corps, becoming the 1st Bomb Squadron (Medium) on 6 December 1939, and the 1st Bomb Squadron (Heavy) on 20 November 1940. During the period 1935–1940 the 1st Bomb Squadron trained aircrews, took part in maneuvers, and participated in air shows. World War II Sixth Air Force The 1st deployed with its parent group on 5 November 1940 on the USAT Chateau Thierry and arrived on 12 November 1940 at Rio Hato Army