Question: In the 'War Room' scene, there appeared to be a sheet of plastic or acetate covering the wall with the map of the enemy's movements. Was that premature for plastic to be available in that size for that time frame?
Answer: It may be polyethylene, which was in wide use by the 1930s. Other plastics were also available at that time.
Answer: It was probably Perspex, an acrylic plastic commonly available at the time, used for, amongst other things, fighter plane cockpit canopies and windscreens.