Birth of the Square Search and the X and Q code.
Found these on the reverse of 101 Sqn Battle Orders for Aug 1941. One details the introduction of the Square Search, and the other is an incomplete document covering the misunderstanding between the navigator and the W/T operator when using the X code. It also mentions the trial of the Q code to replace the X code. The links are to Photobucket.
Square Search
Nav misunderstanding and X and Q codes.