Hybrid electric powertrains for military vehicles offer potential for improved performance, enhanced stealth capability and increased on-board electric power. This paper presents a design of a parallel hybrid electric powertrain for a military tracked vehicle by analyzing its mobility attributes. This involved the component sizing of a hybrid electric powertrain with torque and speed coupling. In this study, two different approaches were used for sizing the powertrain components with a planetary gear unit as speed coupling device. After comparing different speed coupling configurations, the powertrain configuration with connections of the motor to the sun gear, engine to the ring gear, and transmission to the planet carrier provided the least component ratings. Between torque coupling and speed coupling, the powertrain with speed coupling satisfied the given performance requirements with lower motor torque ratings. © 2019 IEEE.