Department of Defense Directive 3020.4: Order of Succession Under Executive Order 13000 and the Federal Vacancies Reform Act of 1998 [open pdf - 71KB]
This Directive reissues DoD Directive 3020.4, "Order of Succession of Officers to Act as Secretary of Defense," July 3, 1996 (hereby canceled) and pursuant to Executive Order 13000, "Order of Succession of Officers to Act as Secretary of Defense," April 24, 1996 and Federal Vacancies Reform Act of 1998 (5 U.S.C. §§ 3345-3349), establishes the order of succession to act as Secretary of Defense, or other Presidentially Appointed, Senate Confirmed (PAS) Officer in the Department of Defense. The order of succession to act as Secretary of the Army, Secretary of the Navy, and Secretary of the Air Force is specified in sections 3017, 5017, and 8017, respectively, of Title 10, United States Code).
Defense Technical Information Center (DTIC): http://www.dtic.mil/dtic/