The above drawing (click to enlarge), which appeared in the 3 May 1934 issue of Flight, depicts an ingenious bombing simulator manufactured by Vickers-Armstrongs -- the Vickers-Bygrave Bombing Teacher. The basic idea is that an image of the area around a bomb target (which is printed on a glass plate) is projected onto the floor, scrolling along to represent the flight of the simulated aeroplane at 8000 or 9000 ft. The bomb aimer peers down at the image through a bomb sight, and sends course corrections to the pilot, who alters the flight path in response. An electro-mechanical linkage then moves the glass plate accordingly.
When the pupil has calculated the direction and force of the wind and has sighted on the target, he throws a switch which represents the bomb release. A device times an interval, equal to the time taken by the bomb to reach the ground, and at the end of this period the movement of the "ground" is stopped. Painted on the floor is a fixed "trail point," which marks the point on which a correctly aimed bomb should drop. Any error may be seen by the difference in the position of the "target" and this fixed trail point.1
Something very similiar seems to have been used by RAF Operational Training Units during the Second World War, though they were then called Air Ministry Bombing Teachers. (Presumably the Air Ministry's in-house version, perhaps improved over the Vickers-Bygrave.) Many former wartime airfields still have their distinctive two-story bombing teacher buildings, for example this one at Waltham. But I don't know how widely such devices were used before the war -- though 601 (Bomber) Squadron of the Auxiliary Air Force, at least, had one in early 1934, according to the article. Given the poor performance of Bomber Command in the early years of the war, one would think that the RAF could certainly have used a few more bombing teachers!
I was thinking that a few bells and whistles could have increased the realism of the Vickers-Bygrave dramatically. For example, dry ice could be used to simulate clouds over the target. You could use a negative, with most of the features painted over, to imitate night bombing. Hydraulics (or manpower!) could be used to buffet the airframe, as in turbulence or anti-aircraft fire (a few firecrackers could help with that too). Not surprisingly, I wasn't the first to have this idea. This interesting site on the history of flight simulation has a page on the Celestial Navigation Trainer (CNT), developed at the RAF's request by the makers of the Link Trainer. Though no mention is made of the Vickers-Bygrave, it's clearly a very similar concept, with the addition of what is effectively a planetarium above, so that the navigator could practice celestial navigation. According to the RAAF (which had one at East Sale), 'The CNT instructor could introduce bumpy flying conditions, changes of wind, create daylight or nightfall, scurry clouds across the sky, or arrange static to worry the wireless operator'. But development of the CNT was initiated as late as 1939, and the first one didn't come into operation until 1941 or later. (The RAAF's remained in operation until the late 1950s, so it must have been very useful.)
Perhaps it's because, as a Gen Xer, I grew up with simulations in a way that previous generations did not, but it seems incredible to me that it took five years or more to take the basic concept of the Vickers-Bygrave and add substantial degrees of realism to it. (Well, I can't completely exclude the possible that this happened sooner, but I have no evidence for that as yet.) Then again, one of the dangers of simulation is that it can reinforce preconceptions, rather than challenge them: to a large degree simulations simulate what is thought will happen, rather than what will actually happen. In other words, garbage in, garbage out. So, maybe the failure to develop a Celestial Navigation Trainer before 1939 is of a piece with the failure to practice bombing runs under warlike conditions in the same period, and the failure to set up a Bombing Development Unit before the start of the war. If bombing is thought to be easy, then there's no need to train too hard for it. Wartime experience was, of course, the ultimate bombing teacher.
See also: this American bombing teacher from 1940, with that wondrous war-winning Norden bombsight fortunately shrouded from public view.