We study whether war service by one generation affects service by the next generation inlater wars, in the context of the major US theaters of the 20th century. To identify a causaleffect, we exploit the fact that general suitability for service implies that how close to age21 an individual’s father happened to be at a time of war is a key determinant of the father’slikelihood of participation. We find that a father’s war service experience has a positive andsignificant effect on his son’s likelihood of wartime service; however, it reduces the likelihoodof the son’s serving in peacetime. We provide evidence consistent with the idea that war serviceincreases the inclination to serve in wars via a process of cultural transmission from fathers tosons, and with the presence of substitutability between this direct transmission and obliquetransmission (from society at large). In contrast, father’s war service increases the opportunitycost of service for sons, consistent with the reduced peacetime service. Taken together, ourresults indicate that a history of wars helps countries overcome the collective action problemof getting citizens to volunteer for war service.