Their experiences were collected. See below from the US Army Military History Institute:
The World War I Veterans' Survey: This survey was begun in 1975, working initially with mailing lists supplied by the Veterans of World War I, USA , Inc., the primary veterans' organization focused on that conflict. The questionnaire was refined and refocused for the particular conflict. One 11-page questionnaire was used at first, although a special questionnaire, slightly revised for naval personnel, was produced for sailors who wished to participate.
USAMHI has received approximately 7000 donations of completed questionnaires and other donated material from soldiers, airmen, Marines, and sailors who served in the time of World War I, whether as part of the AEF, in the continental United States , in overseas possessions, in the occupation of the Rhineland, or in one of the intervention forces in Russia . Once again, just about all major units or branches of service are represented, and the materials are arranged organizationally and then alphabetically within organizational groupings.
A published finding aid, Bibliography No. 20, was prepared in 1986, and provides a listing a description of materials received up until that date.
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