Abstract: A drive mechanism for a tractor, to allow the tractor to be advanced at very slow speeds typically in the range of from 10 to 400 m/h. The mechanism may be mounted on a tractor or on an attachment for a tractor, such as a trenching machine, and rotatably supports a drive shaft which carries a pair of slatted drive wheels such that the wheels are adjacent the rear tires of the tractor. The mounting for the drive shaft is arranged to allow the drive wheels to be moved into and out of engagement with the tractor tires, and a power-drive mechanism is provided for the drive wheels to effect rotation thereof. The power drive mechanism may be adapted for connection to the tractor power-take-off, or could include a separate hydraulic motor.