 Here, the course information of each raid was plotted by Women's Auxiliary Air Force (WAAF), who received information by telephone.Additional intelligence was provided by the Y Service radio posts, which monitored enemy radio communications, and the Ultra decoding centre based at Bletchley Park, which gave the RAF intelligence on the German order of battle.Colour-coded counters representing each raid were placed on a large table, which had a map of Britain overlaid and squared off with a British Modified Grid.