(3) the southeastern United States, to provide a depot necessary to maintain the Air Force; (4) the Pacific northwest, to establish and maintain air communication with Alaska; (5) Alaska, for training under conditions of extreme cold; (6) the Rocky Mountain area, to provide a depot necessary to maintain the Air Force, and for training in operations from fields in high altitudes; and (7) other regions, for the establishment of intermediate air bases to provide for transcontinental movements of the Air Force for maneuvers. (c) I n selecting sites for air bases and depots covered by this section and in determining the alteration or enlargement of existing air bases or depots, the Secretary shall consider the need— (1) to form the nucleus for concentration of Air Force units in time of w a r; (2) to permit, in time of peace, training and effective planning in each strategic area for the use and expansion of commercial, municipal, and private flying installations in time of war; (8) to locate, in each strategic area in which it is considered necessary, adequate storage facilities for munitions and other articles necessary to facilitate the movement, concentration, maintenance, and operation of the Air Force; and (4) to afford the maximum warning against surprise attack by enemy aircraft upon aviation of the United States and its necessary installations consistent with maintaining, in connection with existing or contemplated landing fields, the full power of the Air Force for operations necessary in the defense of the United States, and in the defense and reinforcement of the Territories, Commonwealths, possessions, and holdings. (d) In carrying out this section, the Secretary, on behalf of the United States, may acquire title, in fee simple and free of encumbrance, to any land that he considers necessary— (1) by accepting title without cost to the United States; (2) by exchanging military reservations or parts thereof for that land, upon the written approval of the President; or (3) by purchase or condemnation, if acquisition by gift or exchange is impracticable, (e) The Secretary may, by purchase, gift, lease, or otherwise, acquire at desired locations bombing and machine gun ranges necessary for practice by, and the training of, tactical units. (f) At each air base or depot established under this section, the Secretary shall remove or remodel existing structures as necessary; do necessary grading; and provide buildings, utilities, communication systems, landing fields and mats, roads, walks, aprons, docks, runways, facilities for the storage and distribution of ammunition, fuel, oil, necessary protection against bombs, and all appurtenances to the foregoing. (g) The Secretary may direct the transportation of personnel, and the purchase, renovation, and transportation of material, that he considers necessary to c^rry out this section.