Reserve component (RC) Soldiers, Sailors, Airmen and Marines of the U.S. armed forces have mobilized and deployed in vast numbers since the attacks of 11 September 2001 (9/11). Most of these servicemen and women have been ordered to active duty under Partial Mobilization1 authority provided under the provisions of Title 10, United States Code Section 12302 (10 USC 12302), Ready Reserve, which provides at paragraph (a) thatIn time of national emergency declared by the President after January 1, 1953, or when otherwise authorized by law, an authority designated by the Secretary concerned may, without the consent of the persons concerned, order any unit, and any member not assigned to a unit organized to serve as a unit, in the Ready Reserve under the jurisdiction of that Secretary to active duty for not more than 24 consecutive months [emphasis added].2The law further seeks to ensure equitable distribution of the mobilization burden by providing that “consideration shall be given to—(1) the length and nature of previous service, to assure such sharing of exposure to hazards as the national security and military requirements will reasonably allow;(2) family responsibilities; and(3) employment necessary to maintain the national health, safety, or interest.”3Additionally, many reserve component members have served voluntarily under the provisions of Title 10, United States Code Section 12301 (10 USC 12301), Reserve Components Generally, Section (d), which provides thatAt any time, an authority designated by the Secretary concerned may order a member of a reserve component under his jurisdiction to active duty, or retain him on active duty, with the consent of that member. However, a member of the Army National Guard of the United States or the Air National Guard of the United States may not be ordered to active duty under this subsection without the consent of the governor or other appropriate authority of the State concerned.4The specific language employed in 10 USC 12302 is illuminating: the statute does not empower the President to summon reserve members to duty in any manner that he prescribes but rather, when it comes to involuntary call-ups, constrains the President to calling up “any unit, and any member not assigned to a unit organized to serve as a unit”:5 in other words, the 2 law provides for calling up reserve component members with their units, or where individuals are required, calling them up from the Individual Ready Reserve (IRR). These stated constraints reflect the basic operating assumption underpinning U.S. mobilization concepts, particularly for the reserve components of the Army: Army National Guard (ARNG) and Army Reserve units will be called up as units, and the ARNG and Army Reserve Soldiers serving in units will be called up with and will serve with the units to which they are assigned.In theory, the reserve components mobilize units, but for a number of reasons, reality has departed from this ideal in several respects—there has consistently been a need to call up portions of units or even individual Soldiers apart from their parent units. Factors driving this reality include:• operational requirements in the field;• personnel shortages within mobilizing RC units;• manning policies, including policies related to time at home between deployments and successive mobilizations of the same unit or individual;• policy choices such as emphasizing volunteerism vice involuntary mobilizations;• aversion to calling up servicemembers from the IRR.These and other factors have driven the services to develop a variety of policies and mechanisms for bringing servicemembers onto active duty apart from their home units, often as fillers to bring other RC units up to full strength for deployment or to keep them at strength during deployment, but often to man other requirements not tied to specific RC units as well. Most of these practices have been developed on an ad hoc basis over time; often the policies that direct them have been promulgated only by memorandum or even verbal orders of the Secretary of Defense or others, and have frequently not been codified or compiled in a single, comprehensive volume readily available to the public.6 The processes for mobilizing RC units are arcane, opaque and generally poorly understood except by the specialists who work with them—particularly with regard to the mobilization of individual Soldiers. Understanding is limited even among these technical specialists, however, as persons working in the mobilization field rarely understand the system in a comprehensive way, being experts on the particular matter to which they are assigned but often unaware of how their particular process or policy fits with and impacts other parts of the system.This study will examine the ad hoc reserve component mobilization policies and procedures that have evolved since 9/11, focusing on the reserve components of the U.S. Army and U.S. Air Force (USAF), with a special emphasis on the policies and practices pertaining to the mobilization and employment of individual servicemembers apart from their home units. For purposes of context this study will begin with an examination of how the Army and the Air Force identify reserve component units for mobilization and deployment; it will then examine filler operations—those steps taken to cross-level servicemembers from one unit into another to bring the receiving unit to deployment strength prior to departure for the theater of operations; replacement operations—those steps taken to keep already-deployed units manned while in the theater of operations; and procedures for bringing RC volunteers onto active duty under the provisions of 10 USC 12301.