The US MLRS (field artillery rockets) have changed the way American troops use artillery. The major change has to do with time, particularly the time it takes for the rockets to arrive once the front line troops have called for help in an emergency. The magic numbers are five minutes and 20 minutes. If the troops encounter an unexpected situation and need some MLRS fire, it takes at least five minutes for the fire to arrive. Cannons and mortar can respond much more quickly (two minutes or less). The MLRS launchers park (in a hidden position) 50-150 meters away. The launcher has to move to the surveyed firing point, raise and slew the rocket pods in the same direction, select the number of rockets to be fired and launch. Time in flight takes 25-65 seconds. Thus we have five minutes. The twenty minutes is the time it takes to move to a new position (to avoid counterbattery fire), update location information in the computer and reload the rocket launchers. Again, this is about twice as long as cannon artillery takes to move.