Over the course of the war, the role of the military aviator progressed from one of mere observation to a deadly offensive role. Early on, pilots would would fly off armed only with pistols (or completely unarmed) -- by 1918, fighter planes and massive bombers were in use, armed with multiple machine guns and devastating explosive payloads. Older technologies, like tethered balloons and kites were used on the front lines to gain an upper hand. As aircraft became more of a threat, anti-aircraft weapons and tactics were developed, and pilots had to devise new ways to avoid being shot down from the land and the sky. Aerial photography developed into an indispensable tool to guide artillery attacks and assess damage afterward. The pilots of these new aircraft took tremendous risks -- vulnerable to enemy fire, at the mercy of the weather, flying new, often experimental aircraft. Crashes were frequent, and many paid with their lives. On this 100-year anniversary, I've gathered photographs of the Great War from dozens of collections, some digitized for the first time, to try to tell the story of the conflict, those caught up in it, and how much it affected the world.