Optimal energy flux analysis and design of a power plant for infantry mobility hybrid diesel-electric vehicle is dealt with in this paper. Control strategy management and propulsion system sizing is done on the basis of minimizing total fuel consumption. A quasi-static system model has allowed analyzing the most restrictive operations; moreover the simulation has been used in expected real driving cycles in order to check the performance in typical mission. From the point of view of energy consumption and CO2 emissions, HEV and automatic gear transmission configuration have been compared. The results show a noticeable difference especially in the case of the driving cycle of low-power load conditions, with a very reduced proportion of batteries weight in comparison to vehicle. Fuel and emissions saving with HEV systems compared to automatic geared transmission along vehicle service life justify the higher inversion needed for the HEV system.