Until 1851, the work of the Assistant Postmasters General was assigned on a geographical basis. After November 15, 1851 the Postmaster General assigned work to his assistants on the basis of function, and the Second Assistant Postmaster General was made responsible for mail transportation. As means of transportation were developed and additional services were established, the Office of the Second Assistant Postmaster General became known as a Bureau. In 1946, the Bureau was re-organized and on August 20, 1949 it was abolished and its functions were taken over by the Bureau of Transportation.Most of the records of the Bureau of the Second Assistant Postmaster General described in this inventory were created before the 1946 reorganization. At that time, the Bureau's functions included: supervision of domestic and international mail by means of railroad, electric and cable cars, steam vessels, buses, trucks, or airplanes; supervision of the routing and distribution of the mail; management of international postal service; and supervision of the Bureau's administrative and budgetary services.The records of the Post Office Department in the National Archives on July 1, 1967, amounted to 2,756 cubic feet and comprised Record Group 28, Records of the Post Office Department. These records are described in this preliminary inventory. Forrest Holdcamper has additionally revised and consolidated four earlier inventories: Preliminary Inventory No. 36, Records of the Bureau of the First Assistant Postmaster General, 1789-1942 by Frank J. Nivert and Arthur Hecht; Preliminary Inventory No. 82, Records of the Bureau of the Second Assistant Postmaster General, 1814-1946 by Arthur Hecht; Preliminary Inventory No. 99, Records of the Office of the Postmaster General by Arthur Hecht; and Preliminary Inventory No. 114, Records of the Bureaus of the Third and Fourth Assistant Postmasters General, the Bureau of Accounts, and the Bureau of the Chief Inspector of the Post Office Department by Arthur Hecht, Fred W. Warriner Jr., and Charlotte M. Ashby.