In one aspect there is provided an apparatus to transmit hydraulic force to a snubbing unit's traveling slip assembly. The apparatus comprises a first hydraulic power source having a hydraulic connection to the traveling slip assembly, a hydraulic power source actuator to actuate the hydraulic power source to cause it to transmit hydraulic force to or from the traveling slip assembly. Rotation isolation means are provided to rotationally isolate the hydraulic power source actuator from the first hydraulic power source, and to transfers axial and radial loads between the hydraulic power source actuator 65 and the first hydraulic power source. The first hydraulic power source is mounted to the traveling slip assembly so as to co-rotate therewith.