DEW line, which stands for Distant Early Warning line, was a long-range radar network. It provided the United States and Canada with warning of a possible air attack from the north from 1957 to 1993. The DEW line once extended from northwest Alaska to the east coast of Greenland and had 31 radar stations. In 1985, the United States and Canada agreed to gradually replace the DEW line's aging radars and build additional stations. The upgraded system, renamed the North Warning System, replaced the DEW line in 1993. See North Warning System.