There is continued demand for military vehicles to provide increased fuel economy. Recent trends have appropriately turned to the development of duty cycles that better represent the real-life usage of vehicles. The advent of hybrid electric propulsion and power system architectures offer opportunities for reducing fuel consumption and greater power generation flexibility. The challenge is to effectively quantify the predicted performance for the architectures under consideration using tools that are applicable to shorter development schedules. This paper discusses the importance of using multidomain physics-based computer simulations to perform the fuel consumption analyses. The models used include mechanical, electrical, magnetic and thermal effects, and their intimate interaction in order to predict the fuel consumption for a tracked vehicle traversing courses at varying speed, up and down hills, and negotiating turns. This paper also compares the fuel consumption performance of two tracked vehicles having the same overall characteristics but different propulsion systems; one has a series hybrid electric drive; the other has a conventional mechanical drive. During a 72-hour mission, the series hybrid electric drive consumed ~6% less fuel than a comparable mechanical drive. During the 180-day campaign duty cycle, the fuel savings increased to ~10%.