A lifting barrage was a development in which the barrage lifted periodically to a target further back, such as a second line of trenches. This was countered by the defenders infiltrating troops and machine guns into no-man's land or the areas between their own trench lines, so it was found necessary to comb the entire area of the advance with artillery fire. A creeping barrage (also called a walking barrage) was a barrage that lifted in small increments, perhaps 50 yards, so that it moved forward slowly, keeping pace with the infantry. A rolling barrage was more sophisticated still, with two or more curtains of fire, one behind the other, so that when the batteries firing the rearmost pattern ceased fire to lift the barrage, there was no pause or gap in the barrage. Those batteries lifted their fire to become the forward edge of the barrage, and the pattern was repeated to keep the barrage rolling forward without ever ceasing.
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