A crossfire sets up a pincer action that creates a dilemma in space. Whichever way the enemy turns he makes himself vulnerable to fire from the other direction. The “lifting barrage,” however, creates a dilemma of time. In particular, it exploits the fact that military units need a period of time, however brief, to switch from one activity to another.
The base of fire fires on the enemy position, forcing the enemy to take cover. When the maneuver element is but a few feet from the enemy position, the base of fire “lifts” its fire - shifting it to another target or ceasing fire altogether - and the maneuver element rushes into the enemy position. The enemy, which, until a few moments before, was mainly concerned with avoiding the fire coming from the base of fire, is now trying desperately to get into his firing positions. Unfortunately for him, the maneuver element is already occupying those places.
The lifting barrage was used in the world wars of the last century to attack enemy forces protected by extensive trenches and deep dug-outs. When the timing was right and the maneuver element literally followed the last salvo of shells into the enemy trench, the technique worked well. When, however, the timing was off, and more than a few seconds were allowed to pass between the lifting of the fire and the break-in of the maneuver element, the maneuver element found itself exposed to the undivided attention of an enemy firing at point-blank range.
Other parts of this series:
John Musgrave recounts a British heuristic, the "5, 4, 3, 2, 1 rule". Lift naval gunfire at 500m, rockets/CAS at 400m, 155mm at 300m, 81mm at 200m, and 60mm at 100m. The last hundred yards are covered by direct fire and need to be closed in less than two minutes. This rule preceded precision fires (the RED of a Tomahawk cruise missile is smaller than an 81mm mortar), but it's illustrative, and contra tech fetishists, there aren't limitless stocks of PGMs waiting to support your company attack.
In fire support, as in other parts of life, Timing Is Everything! On Time AND On Target!