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US Navy radar scope in use during World War II. Radar involves the use of reflected radio waves to detect distant objects such as aircraft or ships. These objects show up as bright spots on the screen seen here. The technology existed in the 1920s and 1930s, but the war accelerated the development process. The earliest radar systems were set up in the UK, but the USA also developed its own radar systems. By the end of the war, the US designs had been improved with British technology. This photograph was taken between 1944 and 1945. (KEYSTONE/SCIENCE PHOTO LIBRARY/US NATIONAL ARCHIVES AND RECORDS ADMINISTRATION/ SCIENCE PHOTO LIBRARY)