The endless post-9/11 debate regarding the U.S. military's role in relation to "detention policy" (that is, the various issues associated with the capture, screening, incarceration, and disposition of individuals in the context of combat or counterterrorism operations) is shot through with flawed assumptions. It tends to assume, for example, that if the factual and legal predicates for using military detention without criminal charge can be established in the first instance, then for good or ill that model can be sustained over the long term; that evidence-gathering and other activities associated with criminal prosecution are alien to military training, doctrine, practice and culture; and that a sharp and exhaustive categorical distinction exists between the realm of criminal law enforcement and the realm of military detention without criminal charge. At the highest level of generality, moreover, it presupposes the centrality of law - and by extension the significance of formal legal change - to determining the current and future parameters of the military's role. Not coincidentally, it does all of this through the lens of the Guantánamo Bay detention camp, focusing relentlessly on the peculiar circumstances of the slightly less than 800 individuals who have been detained there.

Few would doubt that the use of detention at Guantánamo matters, or that it gives rise to complex questions of law and policy. But some perspective is in order. The U.S. military has been deployed to Iraq for more than seven years. During that time, it has held approximately 100,000 individuals in custody without criminal charge - this is more than one hundred times the scale of detention at Guantánamo. Once we look beyond Guantánamo to account for the neglected - yet far more representative and extensive - experience of the United States in Iraq, the weaknesses of the aforementioned assumptions come into sharp relief.

First, and most significantly, the American experience in Iraq teaches that the capacity to employ military detention without criminal charge as a practical matter will decay over time. Regardless of whether such detention is legally and factually warranted in the first instance, it ultimately must be abandoned - at least where the detainees are held outside the United States. Changing strategic circumstances - including the dictates of counterinsurgency doctrine, the inevitable assertion of sovereign prerogatives by the host nation, the political infeasibility of importing detainees into the United States or Guantánamo, and the political and diplomatic infeasibility of maintaining covert detention facilities abroad - ensure it will be so. Indeed, the United States is in the midst of experiencing this dynamic in Iraq in 2010, and sooner or later, it will experience much the same thing in Afghanistan.

This insight is profoundly significant - yet rarely noted - for those circumstances in which the United States would prefer that a detained person remain incapacitated over the long term. For persons already in cu stody, it suggests that the United States must plan against the inevitable day when military detention ceases to be available. It further suggests that the United States would be foolish to assume that the currently available facilities in Afghanistan could provide a long-term solution for detainees captured there, let alone detainees captured elsewhere (including the remaining Guantánamo detainees). Long-term incapacitation, on this view, requires a criminal conviction, transfer of a detainee to the custody and control of a third country (for prosecution or otherwise), or resort to lethal force, when legally permissible, in lieu of capture.

Second, while the national debate in recent years has agonized over the prospect of soldiers giving Miranda warnings on the battlefield, a close look at developments in Iraq over the past several years reveals that the U.S. military has already developed a substantial capacity for law enforcement-related activities in the field. The U.S. military has developed this capacity in response to strategic and practical pressures in Iraq dating back to at least 2006. The resulting changes find expression in the priorities of commanders in the theater of war and the attitudes and practices of soldiers at the point of capture in the field.

Awareness of this development will not resolve all issues associated with the prospect of military support for criminal law enforcement. For one thing, these newly evolved capacities exist to support prosecution in the Iraqi criminal justice system, and thus did not develop in the shadow of the full range of procedural complexities that might follow if the end-state involved prosecution in an American court instead. Further, these new capacities do not come without cost. For example, they are in tension with considerations of force protection, at least from a short-term perspective. The important point, however, is that these practices exist today, and no discussion of military support for law enforcement is complete without accounting for them.

The third major lesson from the American experience with detention policy in Iraq is closely related to the second. The evolution of detention-related practices in Iraq over the past seven years illustrates that the range of options for military detention regimes is more numerous, and less static in nature, than the narratives associated with Guantánamo would suggest. The Guantánamo narratives highlight three detention regimes: criminal prosecution, conventional military detention of prisoners of war in accordance with the 1949 Geneva Conventions, and the controversial use of combatant detention without conferral of prisoner-of-war status.

In contrast, the vast bulk of military detentions in Iraq have occurred under the rubric of an ad hoc civilian "security internment" regime that borrowed from, but was not directly authorized by, the Fourth Geneva Convention. The security internment system itself, moreover, evolved through distinct phases, trending over time toward greater protection of rights in keeping with the predictions of the convergence thesis. At the same time, the United States persistently supported the development of the Iraqi criminal justice system as an alternative detention option for dealing with insurgents and terrorists, demonstrating the plausibility of a multiple-track approach, even in the context of a large-scale overseas military deployment. The Guantánamo narratives' portrayal of the array of detention options appears artificially narrow and stultified in comparison.

The fourth and final major lesson yielded by the American experience in Iraq concerns the dynamic relationship among law, policy, and strategic context. More specifically, it concerns the frequent failure to account for that relationship in the context of the detention policy debate. There is some tendency in the existing detention policy debate to treat the relevant legal frameworks as exogenous and static - that is, as deriving from sources independent of the context in which those frameworks might be applied - and hence as resistant to the evolutionary pressures that may arise in the course of application.

The Iraq narrative, in contrast, illustrates both the contextual contingency and flexibility of the law relating to detention. That narrative is, first and foremost, a story of policy change in response to changing perceptions of strategic and operational necessity, occurring within a legal context that itself evolves in both formal and informal ways in response to those same perceptions. This is not to say that legal restraints on detention policy are unimportant or simply a creature of government preference, but rather that efforts to understand the law and policy of detention without accounting for this dynamic are doomed to failure.

These lessons ash; not to mention a host of more specific insights regarding the neglected intersection among law, policy, and actual practice in the field - have immediate implications for U.S. law and policy in Afghanistan. As noted above, the Iraq experience is a stark reminder that the United States cannot count on the perpetual existence of a non-prosecutorial detention option in Afghanistan, so that we should not look to Afghanistan to assist in shuttering Guantánamo. With this insight in mind, the United States is arguably in the midst of an effort to transform its detention practices in the Afghan theater along the lines of its prior experience in Iraq. First, it is markedly enhancing the procedural safeguards associated with the use of detention without charge, responding to the same strategic incentive structure that previously compelled such changes in Iraq. Second, it is doing what it can to stand up a plausible Afghan prosecution alternative, as was also done in Iraq. The Iraqi experience suggests both the utility and the difficulty of succeeding in that effort.

These lessons cannot be gleaned merely by referencing primary legal sources (treaties, statutes, departmental regulations and directives, and so forth) or statistics (the number of persons held, the number prosecuted, etc.), though these elements have their place. The story instead lies primarily in the granular experiences of the Judge Advocates (JAs) and non-lawyer servicemembers who have directly participated in the capture, detention, and prosecution of individuals in Iraq over the past seven years.

In an effort to capture those experiences, I have reviewed a large body of After Action Reports (AARs) that have been systematically collected by the Army's Center for Law and Military Operations. In general, AARs constitute first-hand written accounts from JAs, of varying levels of seniority and types of responsibility, who have recently returned from deployment abroad. They employ a standard format: A single-sentence statement of an issue the JA's unit or command faced, followed by a paragraph or so of commentary on the unit/command's resolution of the issue and on the JA's recommendation regarding the lesson to be learned from the experience. As you might expect, the AARs vary considerably in their level of detail, ranging from generalized or even clichéd statements to detailed anecdotes conveying sharp insights.

Having reviewed hundreds of AARs dating back to 2001, I find that the collection of AARs dealing with capture- and detention-related issues has become considerably more extensive in recent years, which itself is symbolic of the progress the U.S. military has made with respect to the detention policy learning curve in Iraq. The batch of AARs from the 2008-2009 period - encompassing the dramatic change to detention practices associated with the U.S.-Iraq Security Agreement, discussed below - are particularly rich. This Article incorporates commentary from units whose tours in Iraq ended as recently as November 2009.

For all their utility, the AARs are limited in that they do not directly convey the perspective of non-lawyer servicemembers who actually engaged in the capture of persons who then became subject to one form of detention or another. That perspective is critical, yet rarely examined in legal scholarship. Soldiers and Marines engaging in the capture of an individual do so in the shadow of the then-prevailing legal and policy framework for detention operations, and any analysis of that framework that fails to account for its impact on their behavior in the field - and vice-versa - is incomplete in an important sense. In an effort to account for this perspective, I have interviewed and gathered personal accounts from servicemembers of varying ranks, specialties, and periods of service.

The pages that follow divide into two stages. Parts I and II, covering the invasion and occupation phases respectively, are largely introductory. I aim to establish a baseline against which to appreciate the changes that occurred in later years. Part III encompasses the "mandate period" ranging from mid-2004 to the end of 2008. During that period, the U.S. military detained tens of thousands of individuals without criminal charge as "security internees" under the rubric of an ad hoc legal regime established via the UN Security Council, while simultaneously developing an alternative detention track involving prosecution in the reemerging Iraqi criminal justice system. Part IV examines detention law and policy in the "Security Agreement" era, beginning at the outset of 2009 and continuing to the present day. Driven by changing strategic circumstances and associated diplomatic pressures, this regime foregoes security internment authority as a formal matter (though detention without trial persists for some persons in both Iraqi and U.S. custody) in favor of Iraqi criminal prosecution. Part V concludes by distilling the lessons that these events hold for the ongoing detention law and policy debate.