Read it all here.Before ISIS used this tactic, coalition planners and commanders would plan an attack based on their knowledge of a given target in the circumstances ruling at the time, including the construction of a building, the function of the building, nature and type of surrounding buildings, etc. With this information, planners could estimate through a set of institutionalized procedures—the “collateral damage estimation methodology”—potential civilian casualties for a given attack. Understanding the threat to civilians and civilian objects is critical to an informed proportionality analysis as well as effective precautions in attack. Thus, an attack on an arms cache in a warehouse on the outskirts of town, late at night might be judged to present a relatively low risk of civilian casualties. When, however, ISIS has clandestinely fills the building with civilians, this would change the analysis considerably.It is a widely accepted that customary international law imposes an obligation on attacking forces to take “feasible precautions” to minimize harm to civilians and civilian objects. This requirement is captured in Article 57 of Additional Protocol I, and US military doctrine in the Department of Defense Law of War Manual (¶ 5.11). Article 57(1) requires that “constant care shall be taken to spare the civilian population, civilian and civilian objects.” Article 57(2) provides several specific precautions in attack including notably, an obligation to “do everything feasible to verify that the objectives to be attacked are neither civilians nor civilian objects” and the obligation to choose a “means and methods of attack with a view to avoiding, and in any event to minimizing, incidental loss to civilian life, injury to civilians and damage to civilian objects.” The DoD Law of War Manual utilizes similar, but distinct language: “parties to a conflict must take feasible precautions to reduce the risk of harm to the civilian population and other protected persons and objects.” (¶ 5.2.3). (The differences in language are not relevant to our analysis here.). . ..A key element of the precautions requirement is feasibility. As recalled in the official commentary to Article 57, the drafting process involved significant debate over the phrase “everything feasible.” Notably, as recalled in Bothe, Partsh, Solf, the drafting committee rejected an absolute standard (e.g., States shall “ensure”…) in favor of a qualified standard (States shall “do everything feasible”…). A number of countries made reservations regarding this article to emphasize that feasibility was to be judged in the circumstances at the time. The DoD Law of War Manual (¶ 126.96.36.199) expresses a similar qualification, noting that “feasible precautions are those that are practicable or practically possible, taking into account all circumstances ruling at the time.”We suggest that absent intelligence to the contrary, it is not feasible (or reasonable) to assume every building is filled with civilians. It may be the tactic was employed only once by a single ISIS commander and will never be used again. That said, additional precautions must be a taken if intelligence indicates that this tactic is being used regularly, or will be used in the future. It is incumbent upon commanders to assess the intelligence available at the time—to include knowledge of ISIS’ tactics—in determining the nature and extent of precautions that can be taken. The implementation of such precautions leads us to our second point of discussion: how the ROE can be designed to reduce casualties in urban warfare.