It was to do with statistics and the way people were listed in the hospitals. You see what used to happen was a shell would land, short throw a load of clods of Earth into the air, and these would rain down from a very great height onto people and kill them. Those men would be listed as dead but instead after helmets were issued then they would land on the men and injure them they would then be listed as head wounds and that's why there was a sudden massive increase in the number of head wounds recorded in the hospitals.
