Short answers, pulled from the story.
A reconnaissance aircraft is a military aircraft designed or adapted to perform aerial observation, including collection of imagery intelligence through photography, signals intelligence, and measurement and signature intelligence. Modern examples can also carry out real-time surveillance in addition to general intelligence gathering.
In World War I, aircraft were deployed in early phases of battle as the 'eyes of the army' to aid ground forces. They were adapted versions of standard fighters and bombers equipped with film cameras, and floatplanes were also used to locate enemy warships.
A flight of U.S. Navy PBY Catalinas on patrol spotted part of the Japanese fleet approaching Midway Island, which triggered the beginning of the Battle of Midway. The PBY Catalina was a maritime patrol flying boat used by the Allies in World War II.
During the Cold War, the United States developed several dedicated reconnaissance aircraft to monitor the Soviet nuclear arsenal, including the U-2 and SR-71. Other types built for signals intelligence and electronic monitoring included the RB-47, RB-57, Boeing RC-135, and Ryan Model 147 drones.
Helicopters replaced observation seaplanes after World War II. Before that, capital ships had been equipped to carry, launch, and recover seaplanes that could scout beyond visual range and spot artillery fall-of-shot during long-range engagements.
Since the Cold War, much of the strategic reconnaissance role has passed to satellites, and the tactical role has shifted to unmanned aerial vehicles (UAVs). This transition was demonstrated in successful U.S. Desert Storm operations.