One of the main strengths of Artillery fire is the ability to bring down concentrated fire to destroy, suppress or neutralise the enemy. Every soldier knows this, which is why defences and trenches are dug to mitigate the effects. Consequently if surprise can be achieved the enemy is caught in the open before taking cover, maximum casulties are inflicted. In defense, the enemy are not aware of where guns are laid, consequently attacks can be broken up as the surprise of suddenly being hit by effective artillery fire can dislocate the assaulting troops.

A valid point raised by David;

I am assuming that when guns are registered on enemy positions/other guns etc that a number of shells are fired and the resultant fall of shot recorded either by FOO's/recce aircraft/balloon.

However would this not give a wake up call to the other side that their positions are being targetted for attack and therefore attempt to shift their forces/guns out of the way until the opposition bombardment

was completed.

It is indeed an indication that something is about to happen.

As Pete pointed out the use of 'offset registration' or predicted fire is a way of achieving surprise whilst still hitting the target. To achieve this various elements need to be considered, the accuracy of each determining the overall ability to bring down predicted fire.

Good mapping is required in order to calculate basic range and bearing. The difference in altitude (the latter being required as 'non rigidity' affects computations) needs to be determined either by use of artillery instruments or mapping. The position of the guns and the line on which they are laid comes from survey. Ballistic computation requires calibration data for guns (barrel wear affecting muzzle velocities), and consistent shell characteristics. I have just been reading Farndales accounts for the Somme where he states that some 6 inch ammunition varied in length by 4 inches. And as the shell flies through the air it is affected by meteor, consequently corrections to range and / or bearing are required. The degree of inaccuracies of each element could require individual guns to be registered on a target rather than a section or battery.

All of these areas were in their infancy in WW1. In 1914 the doctrine was very much open sights in support of the infantry and cavalry. As the war progressed and indirect fire became the normal method of fire, so mapping and survey by the Royal Engineers developed. The importance of calibration and meteor was recognised and the technical aspects of gunnery became established as opposed to being a black art. With these developments the need to ensure consistency in the quality of ammunition manufacturing was also put in place.

One other aspect which can assist in this whole process is a technique termed ' marking the zone'. I have read a number of accounts where gunners new to an area or OP would look to verify their understanding of the ground by seeing the fall of shot of a few rounds. Thus a single round left, centerer and right of the zone of observation, and a couple at various ridges can aid in reducing the amount of time for 'registration'. From experience this is an effective technique, especially where mapping is poor.

In modern times one of the key questions when conducting fire planning with a supported arm was the degree of accuracy required. This was a trade off between certainty on fall of shot and surprise. In WW1 the Somme was preceded by 6 day bombardment which included registering of targets. I believe by 1917 at Messines, many guns fired on predicted data.

Source: Gun Registration