Combat stress reaction is a mental health disorder first documented in the latter half of the 19th century. But it was not until World War 1 when men were put through the horrific ordeals of trench warfare that the term, “shell shocked” was coined. Many soldiers with shell shock then developed what is now called post-traumatic stress disorder (though the term was not defined until 1983) or acute stress disorder. The prevailing opinion was that these men who had often not suffered from any physical trauma were sufferers of cowardice. The British army created the PIE (proximity, immediacy, and expectancy) principles to get such men back to the trenches promptly where manpower was always needed. It was rarely regarded as a real psychiatric condition, which had two consequences. Firstly, that many soldiers progressed from shell shock to post-traumatic stress disorder and secondly, over 150 soldiers were executed by the British army for, “displaying cowardice” whilst in the grip of the illness. The diagnosis of “shell shock” was to be made increasingly frequently as wars became larger and more mechanized throughout the 20th century. Psychiatrists’ management of such patients initially was primitive and influenced by the zeitgeist that such servicemen were not ill, having never come across such a widespread prevalence of mental health problems until the Great War. These ranged from prescriptions of milk to lobotomies. Understanding how “shell shock” was understood, treated and learning from the mistakes made then, continues to inform management of our patients today.