Wittgenstein’s military identity card during the First World War
Vienna Kriegsarchiv
1918
Ludwig Wittgenstein: The Duty of Genius by Ray Monk (<a href="//commons.wikimedia.org/wiki/Special:BookSources/978-1-448-11267-8" title="Special:BookSources/978-1-448-11267-8">ISBN 978-1-448-11267-8</a>)