The introduction of radio aids to navigation of the hyperbolic type, such as Decca, Gee and Loran, resulted in the need for special charts. These charts, which are usually of the scale and projection appropriate to the occasion, have overprinted on them red, green and purple lattice lines, representing the families of confocal hyperbolae drawn with respect to the Master and Slaves of the radio system. The production of these lattice charts was extensively developed during the war, both in Great Britain and the U.S.A. To provide the mariner with satisfactory marine charts for use with the English Decca Chain, the Hydrographer of the Navy has latticed all the principal coastal charts of England and Wales, and the Danish Hydrographer has similarly latticed the Danish coastal charts.