In 1956 Australia adopted decimal/metric scales for mapping, largely for military interoperability with major allies and the global trend. After the 'one-mile' military maps were discontinued in 1959, and although Defence preferred 1:50,000 maps for tactical operations, it recognised the resources needed for such a programme over large regional areas of Australia and accepted the 1:100,000 map as a practical substitute with 1:50,000 maps over specific areas of interest and military training areas. Then in 1983 Defence endorsed a program for more than 2600 scale 1:50,000 maps in Defence priority areas in north and north-west Australia, its territories and the main land communication routes. By 1996 the Corps had completed more than 1900 of these maps by – field surveys using mainly US TRANSIT and GPS satellite positioning systems and aircraft mounted laser terrain profiling, new coverage aerial photography, aerotriangulation, compilation and cartographic completion on computer assisted mapping systems and produced both digital and printed topographic products.