Diagnosis
The following PIE principles were in place for the "not yet diagnosed nervous" (NYDN) cases:

Proximity – treat the casualties close to the front and within sound of the fighting. Immediacy – treat them without delay and not wait until the wounded were all dealt with. Expectancy – ensure that everyone had the expectation of their return to the front after a rest and replenishment.United States medical officer Thomas W. Salmon is often quoted as the originator of these PIE principles. However, his real strength came from going to Europe and learning from the Allies and then instituting the lessons. By the end of the war, Salmon had set up a complete system of units and procedures that was then the "worlds best practice". After the war, he maintained his efforts in educating society and the military. He was awarded the Distinguished Service Medal for his contributions.Effectiveness of the PIE approach has not been confirmed by studies of CSR, and there is some evidence that it is not effective in preventing PTSD.US services now use the more recently developed BICEPS principles:

Brevity
Immediacy
Centrality or contact
Expectancy
Proximity
Simplicity

Between the wars
The British government produced a Report of the War Office Committee of Inquiry into "Shell-Shock", which was published in 1922.
While recognizing that each individual case of war neurosis must be treated on its merits, the Committee are of opinion that good results will be obtained in the majority by the simplest forms of psycho-therapy, i.e., explanation, persuasion and suggestion, aided by such physical methods as baths, electricity and massage. Rest of mind and body is essential in all cases.The committee are of opinion that the production of deep hypnotic sleep, while beneficial as a means of conveying suggestions or eliciting forgotten experiences are useful in selected cases, but in the majority they are unnecessary and may even aggravate the symptoms for a time. They do not recommend psycho-analysis in the Freudian sense.In the state of convalescence, re-education and suitable occupation of an interesting nature are of great importance. If the patient is unfit for further military service, it is considered that every endeavor should be made to obtain for him suitable employment on his return to active life. Return to the fighting line
Soldiers should not be returned to the fighting line under the following conditions:(1) If the symptoms of neurosis are of such a character that the soldier cannot be treated overseas with a view to subsequent useful employment. (2) If the breakdown is of such severity as to necessitate a long period of rest and treatment in the United Kingdom. (3) If the disability is anxiety neurosis of a severe type. (4) If the disability is a mental breakdown or psychosis requiring treatment in a mental hospital.