Abstract: A top head rotary drive and mast assembly for drilling which is adapted to be readily mounted on a derrick of a conventional truck, crawler or other vehicle so as to be movable from a stored position adjacent the derrick to a deployed position spaced from the derrick for drilling. The mast is adapted to be pivotally connected by at least one upper support arm to the derrick of the vehicle. The deployment and retraction of the mast and the top head rotary drive relative to the derrick are accomplished utilizing either a control device for moving a holding plate which is movable along the mast and to which the top head rotary drive is mounted or by separate lifting device. The invention is also directed to a combination top head drive and mast assembly and drilling rig and method for their use.