The skies over World War I-era Europe served as a brutal testing ground for manned aircraft. Most early fighters were flimsy and frail, and equipment failures and accidents often proved as deadly as enemy gunfire. Upon hopping into the cockpit, even the most skilled pilots had a life expectancy of mere weeks. Though limited by their primitive machines, these “Knights of the Sky” went on to achieve some of the war’s most extraordinary—and often downright suicidal—feats of heroism. Get the facts on six of the Great War’s most celebrated airborne daredevils.