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Flooding as military defense

The deliberate inundating of certain areas can allow a military defensive line to be created. In case of an advancing enemy army, the area was to be inundated with about 30 cm (1 ft) of water, too shallow for boats but deep enough to make advance on foot difficult by hiding underwater obstacles such as canals, ditches, and purpose-built traps. Dikes crossing the flooded area and other strategic points were to be protected by fortifications. The system proved successful on the Hollandic Water Line in rampjaar 1672 during the Third Anglo-Dutch War but was overcome in 1795 because of heavy frost. It was also used with the Stelling van Amsterdam, the Grebbe line and the IJssel Line. The advent of heavier artillery and especially airplanes have made that strategy largely obsolete.