RAF Air Observer
The earlier RAF aircrew role of Air Observer included navigation, bomb aiming, air gunnery, air photgraphy and reconnaisance. It was a lenghty training period. By 1942/3 the four engined a/c were coming into use and decisions were made to split many of the duties of Air Observer - hence a specialist Bomb Aimer role and with the use of powered gun turrets, specialist Air Gunners. Coincidentally the Air Observer role was discontinued and a specailist Navigator role came into being. This specialisation also permitted a significant reduction in training time.
The brevet of an Air Observer - the single-winged "O" (incidentally I believe it was the "oldest" RAF brevet stemming from the artilliary Observers up in their balloons in 1914) was the source of much ribbing by pilots ("Drivers, airframe) - who often called us "Flying orrifices" (or similar). Needless to say we who were privilged to qualify as Air Observers greatly value our position in both Bomber and Coastal Commands of the RAF. Any queries I'll be happy to try and answer them.