World War I

Hitler saw active service in France and Belgium as a messenger for the 16th Bavarian reserve infantry regiment, which exposed him to enemy fire. He also drew some cartoons and instructional drawings for the army newspaper. His behaviour as a soldier was considered somewhat sloppy, but he readily volunteered for dangerous missions such as taking dispatches to and from fighting areas. Unlike his fellow soldiers, Hitler reportedly never complained about the food or hard conditions, preferring to talk about art or history. He was twice cited for bravery in action, receiving the Iron Cross, Second Class in December 1914 and the Iron Cross, First Class in August 1918, an honour rarely given to a Gefreiter. However, because of "a lack of leadership skills", he was never promoted to Unteroffizier. During October 1916 in northern France, Hitler was wounded in the leg, but returned to the front in March 1917. He received the Wound Badge later that year, as his injury was the direct result of hostile fire.

Hitler was considered a "correct" soldier but was reportedly unpopular with his comrades because of an uncritical attitude toward officers. "Respect the superior, don't contradict anybody, obey blindly," he said, describing his attitude while on trial in 1924. One fellow soldier later remarked, "we all grumbled on him and found it intolerable that we had a white raven among us." (Haiden, 1936)

On October 15, 1918, shortly before the end of the war, Hitler was admitted to a field hospital, temporarily blinded by a poison gas attack. Research by Bernhard Horstmann indicates the blindness may have been the result of a hysterical reaction to Germany's defeat. Hitler later said it was during this experience that he became convinced the purpose of his life was to save Germany. Meanwhile he was treated by a military physician and specialist in psychiatry who reportedly diagnosed the corporal as "incompetent to command people" and "dangerously psychotic." His commander at the time said, "I will never promote this hysteric!" (cited from Haiden, 1937) However, historian Sebastian Haffner, referring to Hitler's experience at the front, suggests he did have at least some understanding of the military.

Two passages in Mein Kampf mention the use of poison gas:

At the beginning of the Great War, or even during the War, if twelve or fifteen thousand of these Jews who were corrupting the nation had been forced to submit to poison-gas . . . then the millions of sacrifices made at the front would not have been in vain. (Volume 2, Chapter 15 "The Right to Self-Defence)
These tactics are based on an accurate estimation of human weakness and must lead to success, with almost mathematical certainty, unless the other side also learns how to fight poison gas with poison gas. The weaker natures must be told that here it is a case of to be or not to be. (Volume 1, Chapter 2 "Years of Study and Suffering in Vienna")
Hitler had long admired Germany and during the war he had become a passionate German patriot, although he did not become a German citizen until 1932. He was shocked by Germany's capitulation in November 1918 even while the German army still held enemy territory. Like many other German nationalists, Hitler believed in the Dolchstoßlegende ("dagger-stab legend") which claimed that the army, "undefeated in the field," had been "stabbed in the back" by civilian leaders and Marxists back on the home front. These politicians were later dubbed the November criminals.

The Treaty of Versailles imposed crippling reparations and other economically damaging sanctions, declaring Germany guilty for the horrors of the Great War. The treaty was perceived by most Germans as a humiliation and was an important factor in both the social and political conditions encountered by Hitler and his National Socialist Party as they sought power.