The value of modularity in ground vehicles to the Army and other services has been a topic of much debate for decades. There are instances of successful implementations of modularity in current ground vehicle programs of record. However, these implementations have generally been accomplished through swappable mission equipment rather than large-scale transformation of the vehicle and its core components. Concurrently, the Army Science and Technology (S&T) community has continued to demonstrate the technical feasibility of large-scale, transformative ground vehicle modularity, but the business case of modularity remains elusive. Decision support tools are needed to enable Army leadership to confidently and holistically assess the right balance between modular and mission-specific (conventional) vehicle platforms. This complex problem needs to address numerous considerations, including total lifecycle cost, mission utility, personnel requirements, and fleet adaptability. In this paper we present MARVEL, a modular fleet simulation tool developed to provide decision support when evaluating ground vehicle modularity, and we discuss the tool’s application to a US Army TARDEC vehicle demonstrator program. While MARVEL development is ongoing, we present the current set of results available from our models and discuss the lessons learned that can be gleaned from them regarding the holistic value of a modular vehicle fleet.