Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Both the Allies and Axis powers used radar in World War II, and many important aspects of this conflict were greatly influenced by this revolutionarily new technology. The basic technology of radio-based detection and tracking evolved independently and with great secrecy in a number of nations during the second half of the 1930s. At the start of the war in Europe in September 1939, both Great Britain and Germany had begun the deployment of these systems. In Great Britain this technology was called RDF, standing for Range and Direction Finding, while in Germany the name Funkmessgerät was often used.