FOUR OR MORE Directors of adjoining Districts, grouped into a Region, are subordinate to a Regional Commissioner who is responsible for the policies, work programs, and procedures of the Directors. The Regional Commissioner supervises their operations, provides them with technical advice, and in matters described below stands to them in the position of the Commissioner. Because of the physical size of the United States and because central control of so large an organization as the Internal Revenue Service is difficult, the Commissioner has delegated a large measure of his authority to the Regional Commissioners. Although he has power to group and regroup Districts into a maximum of twenty-five Regions as administrative convenience requires, he has created only nine Regions. The Regional Commissioners represent him, and are directly responsible to him for proper administration in their respective Regions. While their duties are chiefly supervisory, in certain fields their offices also have operational functions. Each Regional Commissioner has a staff of six Assistant Regional Commissioners, concerned, respectively, with administration, collection, audit, intelligence (i.e., fraud investigations), alcohol and tobacco taxes, and appellate work (see the organizational diagram on pages 241-45).