The Distant Early Warning Line, also known as the DEW Line, was a system of radar stations mostly in Alaska and Canada. It was set up to detect incoming Soviet bombers during the Cold War, and provide early warning of any sea-and-land invasion. The DEW Line was operational from 1957 to the late 1980s. Between 1988 and 1993, the stations were deactivated or upgraded as part of the new North Warning System.
Click on "related web page" for a 1958 newsreel about the DEW Line in Alaska and how it was built in a "frozen waste land" that is "no place for human beings".