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Published online by Cambridge University Press: 18 January 2010
Before the war the only radio navigational aids in current use by shipping were direction finding systems, operating in the medium frequency band of the radio spectrum.
During the war, not only were many new types of position fixing systems evolved, but radar techniques were also developed, thus making available a wide range of new facilities of potential use both to ships of many different categories and to port and harbour authorities for the supervision of marine traffic.