If memory serves there are multiple refernces to surface navy grid, KM grid, major ship grid, supply tanker grids, schnell boot and U-boat grids each being constructed on the likely basis of enemy capture. It is further reasonable to assume that the Germans changed the grid when they found out about surrendered U-boats or ships (Altmark & HMS Graph cases in point).Is there any definitive reference to changes in the grid over the course of the war?