I am reading Spitfire V vs C.202 Folgore, Malta 1942 by Donald Nijboer. He has a small picture showing the surface of a fighter pilot's code wheel used to baffle communication between fighter control and pilots. In the caption, he writes "How it actually worked is unknown". Is that actually true? I mean, it doesn't look that complicated; is it more a question of how it was actually used? The wheel as pictured shows a rectangular piece of paper or card divided radially, with another circle of card fastened to the centre. The circle is also divided radially with each section labeled with a letter like 'L', 'T', or 'E'. The segments on the outside rectangle are labeled with place names, numbers, and degree values. For instance the upper left segment is labeled " Grand Harbour, 30, 320° ". So, obviously the circle could be rotated so that 'T' would refer to one of those values on one day or for one flight, but for another it could be rotated so that 'H' indicated those values. I guess there are a couple of segments which have alternate text instead of a place name. In the upper right it reads "Height of cloud base", in the lower right it reads "Carry out recco" and in the lower left "How much cloud?"