525 of the number of officers of the Air Force in that grade authorized for duty in that Bureau. §8497. Air National Guard of United States: members; status in which ordered into Federal service Members of the Air National Guard of the United States ordered to active duty shall be ordered to duty as Reserves of the Air Force. § 8498. Air National Guard of United States: mobilization; maintenance of organization During an initial mobilization, the organisation of a unit of the Air National Guard of the United States ordered into active Federal service shall, so far as practicable, be maintained as it existed on the date of the order to duty. § 8499. Air National Guard in Federal service: status Members of the Air National Guard called into Federal service are, from the time when they are required to respond to the call, subject to the laws and regulations governing the Air Force, except those applicable only to members of the Regular Air Force. § 8500. Air National Guard in Federal service: call Whenever— (1) the United States, or any of the Territories, Commonwealths, or possessions, is invaded or is in danger of invasion by a foreign nation; (2) there is a rebellion or danger of a rebellion against the authority of the Government of the United States; or (3) the President is unable with the regular forces to execute the laws of the United States; the President may call into Federal service members and units of the Air National Guard of any State or Territory, Puerto Rico, the Canal Zone, or the District of Columbia in such numbers as he considers necessary to repel the invasion, suppress the rebellion, or execute those laws. Orders for these purposes shall be issued through the governors of the States, the Territories, Puerto Rico, and the Canal Zone, and, in the District of Columbia, through the commanding general of the National Guard of the District of Columbia. § 8501. Air National Guard in Federal service: period of service; apportionment (a) Whenever the President calls the Air National Guard of a State or Territory, Puerto Rico, the Canal Zone, or the District of Columbia into Federal service, he may specify in the call the period of the service. Members and units called shall serve inside or outside the territory of the United States during the term specified, unless sooner relieved by the President. However, no member of the Air National Guard may be kept in Federal service beyond the term of his commission or enlistment. (b) When the Air National Guard of a State or Territory, Puerto Rico, the Canal Zone, or the District of Colmnbia is called mto Federal service with the Air National Guard of another of those jurisdictions, the President may apportion the total number called on the basis of the populations of the jurisdictions affected by the call.