Hi on a related topic, the sinking area for the U-boats was designated XX with demolition charges to be used. With ZZ and YY as alternate positions if conditions were not suitable. As it turned out both many U-boats and the weather were not and many boats foundered or sunk en-route with a few reaching both ZZ and YY. The latitude and longitude positions for ZZ and YY are listed, is XX position or the Grid position known. John