Any time a Pump Wagon rolls two or more 1s for its movement, it will not move as normal, but instead veers out of control. Re-roll the Random Movement distance (including the extra dice if you were 'pumping harder'), but this time the Pump Wagon will move in a random direction. If the re-rolled movement also includes two or more 1s, then the Pump Wagon has crashed - remove it as a casualty. Otherwise, all Random Movement rules apply, except that a Pump Wagon halted by a friendly unit will inflict Impact Hits (2D6) on the unit that blocks its move.