This paper presents a flexible, modular model architecture in Modelica for system modeling and simulation of military ground vehicles. The model platform and implemented interfaces are flexible enough to support virtual prototyping of conventional and hybrid vehicles with various physical architectures such as series, parallel, hydraulic, and plug-in implementations. Several sample model implementations of conventional and concept hybrid military ground vehicles are presented to illustrate the usage and flexibility of the model architecture to support systems engineering activities by maximizing model re-use throughout the product development process from concept assessment and design through testing and verification.