Why do allies not adapt evenly even in time of war? This article maps and explains differentiation in the development of the stabilization and counter-insurgency doctrines of the British and Germanmilitaries during deployment in Afghanistan. In doing so the study analyses the neglected issue of the organizational capabilities of the British and German militaries to develop and apply military doctrine that is appropriate to the exigencies of the contemporary operational environment. Drawing upon documentary analysis and semi-structured interviews, this article uncovers new empirical material on the institutional reforms which have been undertaken to strengthen the adaptability of doctrine and its application in operations. It finds that while the British military’s organizational capabilities were characterized by deficits at the tactical level between 2006 and 2009, recent years have seen significant improvement. In contrast, the organizational capabilities of the Germanmilitary remain stunted. While international structure is the main independent variable driving doctrinal adaptability, domestic variables exogenous to the military are the dominant intervening factor determining the development of effective organizational capabilities. Neoclassical realism provides the strongest analytical leverage in understanding the factors determining the capacity of militaries to adapt doctrine to the operational environment.