For example, if one enlists for four years active duty in the Army, and then gets out, he/she is placed in the IRR and is subject to recall to active duty for four more years (total of eight years military obligation). If one enlists in the active (drilling) National Guard or Reserves for six years, and then gets out, he/she is placed in the IRR for two years, and is subject to recall during that time.
This is made plain in the enlistment contract. Paragraph 10a of the enlistment contract states:
a. FOR ALL ENLISTEES: If this is my initial enlistment, I must serve a total of eight (8) years. Any part of that service not served on active duty must be served in a Reserve Component unless I am sooner discharged.
Retirees (those who spend at least 20 years in the military and draw retired pay) can be recalled to active duty for life. However, policy established in DOD Directive 1352.1 - Management and Mobilization of Regular and Reserve Retired Military Members, make recall to active duty unlikely for those who have been retired for more than five years, and those over age 60.