The use of aircraft had been useful in World War I. It may not have been used as weapon however; the aircrafts were used to gather information. There were also used as to look out for enemy camps. They used message streamers in order to convey messages.
WW I was the first war that involved the large-scale use of aircraft. At the outset of the war, aircraft were used unarmed for reconnaissance which allowed nations to explore the enemy's area and gain information about their movements and position and the natural features of the area. Eventually, military aircraft improved and airplanes began to drop bombs on strategic enemy locations (which caused major devastation to the enemy) and to carry weapons to do air-to-air combat at close range (also named dogfight), and which provided a new area to fight never seen before: the sky.