The opening months of the First World War caused profound shock due to the huge casualties caused by modern weapons. Losses on all fronts for the year 1914 topped five million, with a million men killed.
This was a scale of violence unknown in any previous war. The cause was to be found in the lethal combination of mass armies and modern weaponry. Chief among that latter was quick-firing artillery. This used recuperating mechanisms to absorb recoil and return the barrel to firing position after each shot. With no need to re-aim the gun between shots, the rate of fire was greatly increased.
Shells were also more effective than ever before. New propellants increased their range, and they were filled with recently developed high explosive, or with multiple shrapnel balls - deadly to troops in the open. Small arms had undergone a similar revolution in efficiency, with the development of high-velocity cartridges filled with smokeless propellant.
The deadly effectiveness of these weapons was not fully realised until the armies clashed. Their efficiency was heightened by the tactics employed. It was thought that, unless soldiers advanced in relatively close order, it would be impossible to command them or maintain their attacking spirit, especially as the Continental armies featured large numbers of reservists, mobilised only at the outbreak of war.
The terrible casualties sustained in open warfare meant that, within four months, soldiers on all fronts had begun to protect themselves by digging trenches.