Abstract: The cooling for large track laying type vehicles is provided by a fan which circulates air through the powertrain compartment and a radiator. The fan speed is varied to reduce the power requirement when maximum air flow is not needed. The speed of the fan is modulated relative to the engine speed by a separate drive mechanism. The electrical generator speed can also be modulated simultaneously with the fan drive. To provide a compact arrangement, the fan input shaft and generator input shaft are coaxially disposed such that the fan structure surrounds the outer periphery of the generator.