Addition: this anecdote was also featured in History Channel's two-part World War II docudrama (which I believe was simply called World War II). According to a reenactment, a young Hitler struggled to put on his gas mask over his bushy mustache during the attack which temporarily blinded him and put him in the hospital. After the attack, he shaves his mustache into the shape we recognize. Is this the case?

Follow-up question: It seems in the 30s and 40s this style of mustache was popular. Did Hitler start the trend, or was he just the most famous person to sport the style.