Trenches are very strong fortifications, and new weapons augmented this even further. Once the lines of trenches had been constructed from the North Sea to the Swiss border, they were very difficult to break out of. Commanders needed to return to the "war of movement" if they were going to win. Many were cavalrymen and were convinced that after the breakthrough horses would achieve a rapid advance into the open country beyond. In wars before 1914, cavalry had played a decisive role including conflicts in South Africa and Sudan. Battles went through the same set stages: after an initial bombardment by the field guns, a terrifying charge by massed ranks of cavalry would take place.

However, this war was different. Here the enemy was not an unsophisticated African tribe armed with spears, but a highly industrialised country. The fundamentals of war had changed. Technology no longer favoured attack, but defence. Artillery, machine guns and other new weapons were so powerful that tactics would have to change. However, the British army, and others, had yet to realise this.

From the beginning the Germans knew that the changes in warfare would make attack costlier in human terms than staying on the defensive. They generally stayed put, as the Anglo-French forces bravely attacked. Germany launched only one major offensive; they attacked at Verdun.

When General Falkenhayn planned the attack at Verdun, he was using a whole new strategy. He knew that Verdun was a symbol of French pride and its loss would shatter the spirit of the French people. Falkenhayn knew that the French would defend it to the last. By using mainly artillery bombardments, with only limited infantry assaults, he hoped to limit his casualties. He calculated that for every German killed, the French would lose three. As the constant and concentrated artillery bombardment had its effect, enemy reinforcements would be brought in to keep the town from falling. These reinforcements would also be killed.

This new, murderous plan was not to capture a physical objective, but to slowly bleed the enemy to death, to wear down the enemy’s ability to attack, and possibly their ability to participate in the war at all. This was a War of Attrition. Men were thought of not as humans, but as numbers. The tactic would yield a victory only after a mountain of corpses had been created. It brought a new meaning to the word "sacrifice". The men who served in it had a name for it : they called it slaughter. Henri Clemenceau, the future French president, served at Verdun and wrote this:

Few attacks went to plan, and at some battles, such as the Somme, it seems incredible that those in command had a plan at all. But there was a generally accepted plan that followed these set stages.

■ Planning and information gathering - Before any major attack months of planning had to take place. To select the best location for an attack, the whereabouts of the enemy’s strong and weak regiments had to be found. Some soldiers were sent on night raids to bring back a prisoner for questioning, whilst others would simply listen to conversations taking place in enemy trenches and hope to pick up helpful information. Letters were censored and diaries strictly prohibited to prevent vital information escaping.

■ Artillery bombardment - After information had been gathered, the attack would begin. Firstly, the artillery would bombard enemy positions to pulverise defences – artillery, machine guns, barbed wire and men (Figs.1 and 4). However, a sustained bombardment signalled to the enemy that an attack would take place soon. This gave time to bring in reinforcements and thus months of work would be wasted.

Note the conical shell in the foreground and the massive recoil mechanism on the barrel

■ Over the top - After the softening up, the artillery fire would cease. This was the signal for men to walk along the communication trenches to the frontline. Here they formed up and fixed bayonets, ready for the officers’ whistles to order to go "Over the top" (Fig.2). Since nothing was meant to have survived the bombardment and enemy defences were supposed to have been paralysed, complicated battle manoeuvres were not thought necessary. Besides, many of the soldiers had been civilians a few months ago, so allowing them to walk normally in long straight lines was thought to be simplest. The infantry could simply walk over and occupy the enemy trenches. A "few" men would be killed by isolated resistance, but such huge numbers of attackers would be used that this would not matter. By the time any remaining enemy soldiers had been mopped up, the second wave of attackers would arrive and continue marching to the enemy’s reserve trenches.

■ Defending captured ground - As soon as men reached the captured trenches, they would madly begin cutting a firestep. Without a firestep, it was very difficult to fire at a counter attacking enemy. If a counterattack was organised within twenty minutes, the trench would often be recaptured by the evicted. .

■ The breakthrough - After the lines of trenches had been captured, marauding cavalry would enter open country to exploit the break in the line, and the "war of movement" would return. Many commanders were cavalrymen and felt they needed to return to the "war of movement" if they were going to win the war.