Sir Douglas Haig 1927
At the beginning of the war, cavalry units were considered by many to be the elite of an army. Many senior officers were drawn from their ranks.
The cavalry had traditionally played a key role as the army's "mobile arm" charging through breaches made in enemy lines to carry through the attack.
Cavalry still proved effective in this role in the Balkans, Eastern Europe and Palestine, but the nature of the Western Front made them almost an anachronism.
Breaches in enemy lines were rare and even when they occurred the cavalry where immobilised by the trenches and wire defences. They were also hopelessly vulnerable against the power of modern artillery.
Many senior officers blinded themselves to the reality of the situation, wasting huge resources on maintaining cavalry regiments when they could accomplish nothing. By the end of the war the majority of cavalry that had actually fought were dismounted and used as infantry.
This failure of the cavalry reinforced the need to discover another "mobile arm" capable of overcoming the problems of the "new" warfare.
This need was only satisfied by the development of the tank.