This article develops an analytical model of force-composition that combines the advantages of conscription with those of an all-volunteer force. Using Israel as a hypothesis-generating case study, it argues that mandatory military service has undergone changes centered on five key organizing principles: selective conscription, early discharges, elongated lengths of service, forms of voluntary service and differing pay-scales and other material and non-material incentives for conscripts. These principles are “grafted” onto conscription creating a hybrid, “volunteer-ized”, model. The utility of the theoretical model lies in explaining how these principles facilitate mobilizing a needed number or recruits, providing an adequate level of military expertise, as well as maintaining the legitimacy of the armed forces by meeting domestic social, economic and political expectations about its composition and the use of personnel at its disposal. The system is adaptive and flexible, as shown in throughout the comparisons throughout the paper.