(Bonus) WWI: Aviation during the War

(Bonus) World War I was the first major conflict involving the large-scale use of aircraft. Tethered observation balloons had already been employed in several wars, and
would be used extensively for artillery spotting. Germany employed Zeppelins
for reconnaissance over the North Sea and Baltic and also for strategic bombing
raids over Britain and the Eastern Front.
Airplanes were just coming into military use at the outset of the war. Initially, they were used mostly for reconnaissance. Pilots and engineers learned from experience, leading to the development of many specialized types, including fighters, bombers, and trench strafers.