Complex sentence: However this is difficult to achieve, as classic artillery grows in weight dramatically as the range is increased, artillery capable of supporting an army over a front of, say, 250 km, would be considerably heavier and slower moving than a number of smaller guns.
Split into simpler sentences: However this is difficult to achieve, as normal artillery grows in weight dramatically as the range is increased. Artillery capable of supporting an army over a front of, say, 150 km, would be considerably heavier and slower moving than a number of smaller guns.