During World War I it became apparent that the trials and tribulations of modern warfare were giving rise to a newly recognized type of battlefield casualty -- men who were apparently physically sound, but after spending time in bombardment zones became nervous wrecks. This was dubbed 'shell shock', and was often not treated by anything more advanced than removal from the front line, although it was discovered that psychotherapy was a relatively effective treatment for chronic cases.
With the event of World War II the British Army tried to find proactive measures to inoculate soldiers to the effects of war through the use of battle schools. These were training grounds in which the soldiers trained with live ammunition, experienced mock explosions, and accustomed themselves to the sounds and experiences of the battlefield.
However, British officials did not stop there. In late 1941 they set up the British Hate Training Academy. On the theory that any righteously enraged soldier was less likely to suffer a breakdown, they set up a series of exercises designed to encourage the soldiers to hate the enemy. These included viewing pictures of war atrocities (rotting corpses and starving and sick prisoners) berserker-type trainings where they watched sheep being slaughtered and smeared themselves in blood while screaming in rage, and attacking dummies that would splatter them in fake blood.
This did not go over well with the British public, and it became a brief political cause, with decriers claiming that it was an un-British practice. There were some senior commanders who agreed with this, and, moreover, the training didn't actually seem to be producing the desired results. By May of 1942 the hate training was discontinued.
World War II Infantry Tactics: Squad and Platoon by Stephen Bull
Electrified Sheep by Alex Boese