From lead lines to multibeam sonar

Older charts were built from laborious point soundings taken with weighted lines, a method that made specialized ships difficult to justify. Single-beam sonar required ships to cover the seabed in tight tracks, while multibeam systems greatly expanded the area measured at once. The painstaking surveys that enabled British forces to move upriver during the Quebec campaign show how even lead-line hydrography could determine the feasibility of an amphibious operation. This technical progression also connects the still incomplete mapping of the oceans with the exchange of knowledge between civilian hydrography and naval sonar. The gaps were large enough to prompt debate over whether whole tectonic plates had been missed, although that conclusion was probably wrong. Better detection tools do not eliminate the submarine threat, but they materially improve the information available to anti-submarine forces.