Introduction to the special section on some less-well-known contributions to the development of radar: From its early conception until just after the Second World War

The invention of radar is 112 years old. A continuing interest has been and is being addressed in the long history of radar, with many old as well as recent publications. However, historical data on radar research and development are spread over many archives in the many nations where the independent and secret development of military radars almost simultaneously started in the 1930s, leaving important material still to be analyzed in both national and private archives. Moreover, unreliable and biased documents exist on this sensitive topic, calling for a wise usage of the written material. As a result of recent and careful archive research (and a result of some personal interviews), done by leading radar experts from four different nations, this special section presents numerous interesting, less-known (in some cases, unknown) elements concerning the development of radar before and during the Second World War (WW II) in France, Ukraine (and former USSR), South Africa, and Hungary.