At the onset of the First World War in September 1914, Kirchner volunteered for military service. In July 1915 he was sent to Halle an der Saale to train as a driver in the reserve unit of the 75th Mansfeld Field Artillery Regiment. Kirchner's riding instructor, Professor Hans Fehr, arranged for Kirchner to be discharged after a mental breakdown. Kirchner then returned to Berlin and continued to work, producing many paintings including "Self-Portrait as a Soldier" (1915); in December 1915 he was admitted to Dr. Kohnstamm’s sanatorium in Königstein in Taunus, where he was diagnosed with a strong dependency on Veronal, and alcoholism. In a letter to Dr. Karl Hagemann, a friend and patron, Kirchner writes: "After lengthy struggles I now find myself here for a time to put my mind into some kind of order. It is a terribly difficult thing, of course, to be among strangers so much of the day. But perhaps I’ll be able to see and create something new. For the time being, I would like more peace and absolute seclusion. Of course, I long more and more for my work and my studio. Theories may be all very well for keeping a spiritual balance, but they are grey and shadowy compared with work and life". Throughout 1916, Kirchner periodically returned to Berlin for a few weeks at a time to continue his work at his studio; he also produced a series of oil paintings, and many drawings, during his stays in Königstein. After an exhibition of his work at the gallery of Ludwig Schames, in Frankfurt am Main, in October 1916, Kirchner sold many works and began to do well financially. In December, he suffered from a nervous breakdown and was admitted to Dr. Edel’s sanatorium in Berlin Charlottenburg.