The study of processes leading to the militarization of landscapes is a rapidly expanding field of research. While certain themes, such as the impact of conflicts on landscape transformation, have received significant attention, others remain comparatively under-examined. Specifically, the environmental consequences of military training activities on inland freshwater ecosystems in the context of war preparedness have been largely overlooked by historians. This topic, however, falls within the dimension of militarized landscapes, encompassing lakescapes and the related environmental processes that undergo transformation due to conflict preparation. This article aims to address this gap by exploring a specific typology of underwater munitions sites: former military training targets and ranges located within inland freshwater bodies, with a particular focus on Lake Michigan in the United States and Lake Neuchâtel in Switzerland. By contextualizing these sites within a historical framework and examining their commonalities and differences in training practices, this interdisciplinary research will discuss the current management—or lack thereof—of this military legacy resting at the bottom of the lakes. The aim of this research is to highlight how lakescapes have been transformed by military training and how such practices have environmentally impacted inland freshwater bodies. This study finds that these military activities were not concealed from the public, that they have environmental consequences, and that they consistently receive less attention than terrestrial sites.