The air service medical laboratory reckoned that 80% of groundings of aircrew were due to nervous disorders, and 50% of pilots developed serious neuroses during their tour of duty.
From Trauma and Recovery by Judith Herman:
Mental breakdowns represented 40% of British battle casualties(all forces?). Military authorities attempted to suppress reports of psychiatric casualties because of their demoralizing effect on the public.
Initially, the symptoms of mental breakdown were attributed to a physical cause. Psychologist Charles Myers, who inspected some of the first cases, attributed their symptoms to the percussive effectsof exploding shells, and called the disorder "shell shock".
When it was found to be a mental rather than physical issue, traditionalists put it down to poor moral character. A soldier should glory in war and betray no sign of emotion. Certainly he should not succumb to terror. A soldier with a medical neurosis was a "moral invalid", at best a constitionally inferior human being, at worst a malingerer and a coward. Some military authorities said they should be court martialed or dishonourably discharged, rather than given medical treatment. Psychiatrist Lewis Yealland treated them with increasing electric shocks until their symptoms went away.
Progressive psychologists such as W.H.R.Rivers wanted to treat on psychological lines. He created a safe environment where people could talk through their experiences and fears, until fit to return to the battle.
Showalter; The Female Malady
A. Leri; Shell Shock: Commotional and Emotional Aspects
C.S.Myers; Shell Shock in France
Peter Barham; Forgotten Lunatics of the Great War
Masculinity and the Wounds of the First World War: A Centenary Reflection; Carden-Coyne, Ana
A Predisposition to Cowardice? Aviation Psychology and the Genesis of Lack of Moral Fibre; English, Allan
The Nervous Flyer: Nerves, Flying and the First World War; L.S.Cobden; Br J Mil Hist. 2018 Feb 2; 4(2): 121–142.
The Image of Shell Shock: Psychological Trauma, Masculinity, and the Great War in British and American Cinema by Jobe Close - PhD thesis
Shell Shock - BBC Inside Out
Voices of the First World War: Shell Shock - Imperial War Museum
Open Learn: The First World War: trauma and memory
Shell-Shock and Medical Culture in First World War Britain; Tracey Loughran
War Neuroses and Arthur Hurst: A Pioneering Medical Film about the Treatment of Psychiatric Battle Casualties Edgar Jones
War Psychiatry and Shell Shock 1914-18 Online
The origins of British military psychiatry before the First World War - Edgar Jones - shell shock from the Crimea to the start of WW1
Legacy of the 1914–18 war: Battle for the mind: World War 1 and the birth of military psychiatry; E. Jones, S. Wessely
Somatoform Dissociation in Traumatized World War I Combat Soldiers; A. Van Dijke, O van der Hart
Wounds and Dirt: Gendered Metaphors in the Cultural History of Trauma; Lisa Malich
The neurological manifestations of trauma: lessons from World War I; E. Jones
Shock Troupe: Medical Film and the Performance of 'Shell Shock' for the British Nation at War; Julie M. Powell
Visualizing ›War Hysterics‹: Strategies of Feminization and Re-Masculinization in Scientific Cinematography, 1916–1918; Julia Barbara Koehne
Reanimating the Wound: Dermatilliomanic Practice and the First World War; C. Nock; PhD thesis
How the Royal Flying Corps' 'Superman' 'Image Masked a Crisis of Nervous Disorders During WWI; Joseph Hayes