During the Second World War, Tenterfield became the focal point for the alleged 'Brisbane Line'. The Brisbane line was to be the site for the second defense of Australia if the country was invaded from the north. It followed a rough line heading west along the NSW QLD border. The idea was to try and block all the major access routes heading south, one of these routes was on the Clarence River near Tenterfield. At Paddy’s Flat are the remnants of an old tank trap, huge concrete triangles were used to span a bottleneck in the river, they are probably the only remaining evidence of what was supposed to be the Brisbane line. Politically, nobody really wants to acknowledge the existence of such a plan, as the idea of sacrificing most of Queensland seemed a fairly desperate measure.
During World War Two thousands of troops were based in Tenterfield, nine separate camps were spread around the town, at times testing the towns capacity to deliver food and services.