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Research Questions

  1. What are the differences in how rapidly active and reserve component forces can get ready to deploy abroad in a crisis?
  2. What are the comparative costs of using active and reserve component forces to provide a sustained level of deployed output for rotational missions?

New defense strategic guidance and budget reductions as the United States draws down its forces in Afghanistan have led the Army to reassess how it balances the mix of forces between its active component (AC) and its two reserve components (RCs), the Army National Guard and the U.S. Army Reserve. Multiple factors should influence AC-RC force mix decisions, including the capabilities that AC and RC forces provide and their cost. This report describes analyses from an ongoing stream of RAND research on the Army's AC-RC force mix. It focuses on two critical aspects of capabilities and cost: (1) the time needed to make forces ready to deploy abroad in a crisis and (2) the costs of AC and RC forces to sustain the same level of deployed output for rotational missions. It finds that the factors that make RC units cost less than AC units, on average, can also make them less rapidly deployable in the event of unexpected contingencies — namely in terms of the amount of time personnel are available to train. The report also identifies the circumstances under which either AC or RC forces can sustain a given level of deployed output at a lower cost. Finally, it shows that differences in capabilities and cost depend of the type of unit. For example, many smaller support and logistics units tend to have an advantage in the RC, while some larger ground combat and aviation units have an advantage in the AC. Policymakers should consider both capability and cost as they weigh AC-RC force mix decisions.

Key Findings

Force Mix Decisions Must Account for Differences in the Capabilities That Active and Reserve Components Provide, as Well as Differences in What They Cost

  • In sustained operations, like those in Iraq and Afghanistan, U.S. Department of Defense policy permits reserve component (RC) units to deploy less often than active component (AC) units; this means that it takes two or more RC units to provide the same deployed output as one AC unit.
  • Because of the larger number of RC units needed, in some cases it can be more expensive to sustain the same deployed output with RC units than with AC units.
  • Because they must finish training after they mobilize, RC units take longer to get ready to deploy in a crisis compared with AC units that have completed training. In some cases, RC units may not be able to finish training and deploy in time to meet a commander's needs.
  • Differences in output and cost depend on the type of unit: Many smaller RC units can get ready to deploy relatively quickly after mobilization, and they are also more likely to show a cost-per-output advantage for sustained operations; larger RC ground combat and aviation units take longer to complete postmobilization training and can be more expensive for the same sustained output than AC forces.


  • Policymakers should consider both capability and cost as they weigh AC-RC force mix decisions.

Research conducted by

This research was sponsored by the U.S. Army Deputy Chief of Staff, G-8, Quadrennial Defense Review Office, and conducted within the RAND Arroyo Center'sStrategy and Resources Program. RAND Arroyo Center, part of the RAND Corporation, is a federally funded research and development center sponsored by the U.S. Army.

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