Abstract: A tensioning device for maintaining proper belt tension on the drive belt of a tracked vehicle. The flexible drive belt extends between a drive wheel and a carriage mounted free wheel. An idler device dynamically adjusts the tension on the drive belt, and includes a drive wheel mounted to a frame, a carriage slidably mounted to the frame and supporting a free wheel, a hydraulic cylinder mounted to the frame and engaging the carriage for applying a force to the carriage. A hydraulic control circuit operates the hydraulic cylinder, the control circuit being adapted to adjust the pressure in the hydraulic cylinder to apply a first force against the carriage in response to a first detected condition, such as during normal forward operation of the vehicle. The control circuit is further adapted to apply a second force against the carriage in response to a second detected condition, such as during reverse operation of the vehicle.