A steerable knuckle, and an axle and track drive assembly including the knuckle, is disclosed. A driveshaft rotatable about a rotational axis extends through the knuckle. The knuckle pivots about a steering axis generally perpendicular to the rotational axis. The driveshaft extends through an axle housing, and a hub is coupled to the driveshaft. The track drive includes a drive wheel, a drive frame, rollers, and a track. Rotation of the driveshaft about the rotational axis rotates the hub and drive wheel which rotates the track about the drive wheel and rollers. Rotation of the knuckle about the steering axis turns the track drive. The knuckle can include a hollow spindle, one or more undercarriage support arm(s) for connecting the track drive frame, steering stops, and king pin, steering cylinder, and tie rod connections. The knuckle can be a single integrated piece.