Reconnaissance aircraft have always been less glamorous than fighters. They don't have much if any direct effect on the enemy, but rather serve as a kind of enabler to other forces.
The very first attempts of military aviation (with balloons) were aimed at observation. Air/air and air/ground combat came later.
The bombers of the First World War were quite fragile and unsafe aircraft which were only able to carry and drop rather modest bomb loads. Their pilot's only means of dropping these bombs accurately was flying low - low enough to expose the crew to effective rifle and machine gun fire from the ground.
Few armoured aircraft were developed for air/ground attacks before 1919, among them several German types (among them the very advanced metal fuselage J 10) and the British Sopwith Salamander. These emphasized the use of machine guns against ground targets, but the overall concept was a rather awkward one.
|Junkers J 10|
Artillery observation from a safe altitude, equipped with map and radio transmitter was much more useful than bombing and strafing runs. Aircraft were already able to serve as forward observer tools for the great might of the artillery arm and thus able to bring down extreme amounts of ammunition on spotted targets - much unlike the bombers.
This principle flourished in 1918 when the Entente powers had gained air superiority through vastly superior aircraft production and pilot training figures as well as through aggressive tactics.
It became the primary idea of air-ground cooperation of the 20's and 30's. A whole category of aircraft - army cooperation aircraft - was defined to accomplish such missions.
The Hawker Audax was a typical example in the inter-war years.
These artillery spotters didn't meet the expectations in wartime, though. Efficiency demanded that they had to fly alone or with minimal escort and by 1940 they lacked the speed and climb rate needed to evade fighters. Improved army air defences such as 37 and 40 mm light anti-air artillery (AAA) were able to deny low altitudes (below 3,000 m) to these aircraft at least in the divisional rear areas.
They were useful, but apparently so primarily at the edge of friendly troops and in area with total air superiority. The L-series of U.S. observation (liaison) aircraft such as the Stinson L-5 was able to exploit such conditions late in the war, for example.
Being hampered in their potentially most influential role, many of the wartime army cooperation aircraft were used to transport officers, documents and wounded troops instead. Having someone with a radio in the sky, loitering over a division on the march can be very useful for coordination and security as well.
The whole concept came under pressure with the rise of helicopters in these secondary tasks during the Korean War. It wasn't before the Vietnam War (which largely lacked effective hostile fighters over South Vietnam) that the artillery observation planes rose to prominence again. They got a nicer name; forward air controllers (FAC). This time, they also served as guides for bombers and were thus equipped with unguided rockets for marking the target area visually.
These aircraft were of great importance in Southeast Asia at that time. Meanwhile, they were not expected to be really relevant in Europe. Why? Well, they wouldn't have been survivable in World War 3. Sure, a very slow aircraft is difficult to hit for a supersonic aircraft, but it can be done. Crews of radar-guided anti-air guns would consider these aircraft as mere target practice, and an easy one!
These aircraft got subsequently little attention after the Vietnam War. Well, observation helicopters continued the encroachment into the realm of the observation aircraft. An example was and is the OH-58 Kiowa.
The whole category of a quite slow, persistent eye over the battlefield fell nevertheless way behind fighters and bombers in regard to attention - until 2003. The occupation wars began, there was no effective hostile air defence or even fighter aircraft arsenal and ground forces needed an eye in the sky to serve them yet again.
This time extreme endurance drone took over and became the new sexy craze in aviation technology. They got lasers instead of white phosphorous rockets for target designation, a thermal cameras ball instead of human eyeballs and a satellite data-link instead of a normal radio. The Predator drone was the early example, but again there was a wartime increase in weight, complexity, versatility and armament.
And yet again, people tend to forget that these fragile aircraft wouldn't be of any actual use in a real war. Instead, they would simply be shot down by a hostile military. The Georgians were taught this lesson in 2008 by Russia the hard way.
This begs the question: When do the last people understand that loitering over the head of your enemy is really only practical if your enemy is really, really incapable?