A hydraulic drive system has a variable displacement hydraulic pump; a prime mover driving the hydraulic pump; a variable displacement hydraulic motor fed hydraulic fluid by the hydraulic pump, the hydraulic motor having internal torque control and speed modulation via the variable displacement; and a shaft driven by the hydraulic motor. The prime mover is either an electric motor or an internal combustion engine, advantageously a diesel engine. The system is either an open loop hydraulic system or a closed loop hydraulic system. With the system, relatively low output prime movers are used without reduction in the systems maximum torque output.