Battle of the Somme

Hitler served in France and Belgium in the 16th Bavarian Reserve Regiment (called Regiment List after its first commander), ending the war as a Gefreiter (equivalent at the time to a lance corporal in the British and private first class in the American armies). He was a runner, one of the most dangerous jobs on the Western Front, and was often exposed to enemy fire. He participated in a number of major battles on the Western Front, including the First Battle of Ypres, the Battle of the Somme, the Battle of Arras and the Battle of Passchendaele. The Battle of Ypres (October 1914), which became known in Germany as the Kindermord bei Ypern (Massacre of the Innocents) saw approximately 40,000 men (between a third and a half) of the nine infantry divisions present killed in 20 days, and Hitler's own company of 250 reduced to 42 by December. Biographer John Keegan has said that this experience drove Hitler to become aloof and withdrawn for the remaining years of war.

http://en.wikipedia.org/wiki/Adolph_hitler