With many U.S. allies bracing for imminent cuts to defense budgets, and with U.S. Defense Secretary Robert Gates engaged in a campaign against profligate spending at the Pentagon, the military reserve components -- which frequently suffer disproportionately from reductions in defense spending -- might make for a tempting target. But cutting back on these crucial elements of modern Western militaries would be a mistake with significant operational consequences.

As in other countries, the U.S. military reserve structure reflects the nation's distinct historical origins, security requirements, and constitutional principles. But the U.S. Department of Defense is unique in possessing seven major distinct reserve components(.pdf) within its subordinate military departments. The Army has two reserve components: the U.S. Army Reserve and the Army National Guard. The Air Force contains two reserve components as well: the Air Force Reserve and the Air National Guard. The Navy has three reserve components: the Navy Reserve, the Marine Corps Reserve, and the Coast Guard Reserve, which falls under Navy control in wartime. 

During the past two decades, the world's great military powers have come to rely increasingly on their reserve components. Previously, defense planners treated their reservists as strategic assets to be mobilized perhaps once in a lifetime, for a war comparable to World Wars I and II. Since then, these strategic reserves have become operational reserves, called up every few years -- and often several times in their careers -- as integral members of their country's "total force." 

Several key factors explain the increased importance of military reserves in recent years. First, the Cold War's end has eliminated the need to maintain mass militaries capable of waging total wars. By contrast, the conflicts of the post-Cold War era have been protracted but limited in geographic scope. Since Desert Storm, the most common wars have been internal conflicts such as insurgencies, civil wars, humanitarian interventions, and post-conflict stabilization operations -- situations for which defense ministries do not need large numbers of active soldiers or the capacity to mobilize large number of reserves. 

Second, these types of military conflicts require skills most widely available in the civilian world, especially those found among civil governance experts such as small town mayors, police trainers, agronomists, and entrepreneurs. As for new forms of warfare that many fear could involve the major powers, such as cyber strikes or biological weapons attacks, they, too, involve skills where the civilian sector -- computer companies and biotech firms, for example -- enjoys a comparative advantage to the military. 

Reservists also have unique advantages in taking the lead in homeland defense missions. They are effectively "stationed" on-site, as it were, in the stricken communities, and therefore enjoy superior situational awareness. They often work as first responders in the police, medical, and fire-fighting professions while they are also serving as part-time military reservists. And in some countries, such as the United States, they have enhanced authority to engage in domestic law enforcement. This homeland defense function has recently been extended to providing security at major events, such as large sporting competitions or presidential inaugurations, against possible terrorist attacks. 

This transformation has not come without challenges.

If reservists are to be used more like active duty forces, and ideally be interchangeable with them, then they also have a moral claim to receive the same health care and other benefits as the active duty forces. There is also a practical reason to harmonize their organizational structures, compensation packages, equipment, training, and other treatment, since it reduces reservists' perceptions of having "second-class" status and makes them more interoperable with active duty forces. But offering Reserve Corps troops the same benefits as their active duty colleagues would be very expensive, undermining the perceived cost-advantage of retaining part-time forces. 

Second, defense managers must decide which skills are needed in the active and reserve components, and then "rebalance" them accordingly. The Pentagon has struggled with this issue for years. Immediately after the end of the Cold War, it decided to concentrate some skills -- such as specialized medicine, civil affairs and military police -- in the reserve component, since they were rarely needed. But then the wars of the former Yugoslavia, Afghanistan, and Iraq drew heavily on these assets. More recently, the U.S. Defense Department has sought to ensure that enough specialized skills reside in the active component to allow the Pentagon to go to war without needing the reserves for a few weeks. But many in the military feel it is important to require a reserve call-up for any major American military engagement, to ensure that the president cannot wage wars without impacting the general population outside of the full-time active-duty branches. It is hoped that this will in turn ensure that sufficient public support exists to see the mission through to its conclusion.

Some employers also have not welcomed the burden of periodically losing a member of their team to a year of military service. Certain countries, such as Canada, rely primarily on private-sector advocacy groups to appeal to employers' patriotism to hold open reservists' jobs while they serve. But in many countries, including the United States, federal law prohibits discrimination against reservists in the work place and requires that their post be kept open while they serve. 

Several countries' defense ministries have also sought to help companies manage their reserve employees better, as well as to relieve stress on reservists' family lives, by making rotation cycles more predictable. This often takes the form of limiting the frequency of a reservist's year of active duty to once every five or six years. But the Pentagon has only been able to approach this level for most reservists by hiring more soldiers and considerably reducing the U.S. military footprint in Iraq. 

Militaries are also allowing reservists greater freedom to "switch lanes" back and forth between the active and reserve components, empowering them to participate full- or part-time in the military as interests and circumstances allow. Of course, this freedom complicates military planners' ability to anticipate the size of their current force as well as projected recruitment and retention needs for each reserve component. 

The transformation in the use of reserve components has also complicated the cost-benefit calculations that go into policymaking. The increasingly complex factors that must now be considered include opportunity costs resulting from foregone productivity contributions to civilian employers, the benefits employers derive from government-provided training in leadership and technical skills for their employees, and the intangible benefits that citizen soldiers provide in linking the military profession to civilian values and perspectives. 

As a result, it is unclear whether extending additional financial benefits to reservists would improve national military capacity more than would allocating those same funds to regular active-duty units. Policymakers and analysts tend to focus on the input side of the equation (e.g., how much is spent on each component) rather than on the outputs (how spending changes affect net military capacity), since evaluating the latter is more difficult. 

The Pentagon has struggled with this last issue. This year's Quadrennial Defense Review(.pdf) directed the Defense Department to undertake a comprehensive study of the actual costs of the reserves, with the results due in January. The fear is that reservists' true value will only become apparent after many NATO governments have already committed to reducing their numbers and degrading their training and equipment -- a classic case of not missing the water until the well runs dry. 

**Richard Weitz is a senior fellow at the Hudson Institute and a World Politics Review senior editor. His weekly WPR column, Global Insights, appears every Tuesday.