Short answers, pulled from the story.
French forces lifted fabric balloons into the sky to watch enemy movements during the Napoleonic Wars. Observers in wicker baskets recorded troop positions and artillery placements for commanders below.
A flight of U.S. Navy Catalina flying boats spotted part of the Japanese fleet approaching Midway Island on the 3rd of June 1942. This visual confirmation triggered the Battle of Midway and demonstrated the value of maritime patrol reconnaissance.
The United States developed dedicated designs like the U-2 and SR-71 to monitor Soviet nuclear arsenals during the Cold War. The USAF SR-71 became a symbol of this technological race between superpowers.
Specialized roles emerged for signals intelligence and electronic monitoring through aircraft like the RB-47 and Boeing RC-135. These machines collected data on enemy communications and radar systems rather than just visual imagery.
Since the end of the Cold War, much of the strategic reconnaissance role has passed over to satellites. Tactical operations increasingly rely on unmanned aerial vehicles instead of manned aircraft.