After the first successful flight by the Wright brothers in 1903, the age of aviation was born, and by 1910 army commanders in the United States and Europe began ordering aircraft and experimenting with them. But at the outbreak of World War I in 1914, no-one could yet possibly know how significant a role they would play in the fighting. Aerial reconnaissance, observation and photography impacted the fighting in many ways, but little has been written about it. Balloons and airplanes regulated artillery fire, infantry liaison aircraft followed attacking troops and the retreats of defenders,...