North American Alert and Warning Networks

Pine Tree Line – radar, planned 1946, handed over to Canada on 10Jan55

Mid-Canada Line or McGill Fence – 1956-1965
DEW Line – radio frequency tripwire 1957-1993, most deactivated 1988, the remaining upgraded
Green Pine Network – UHF, designed 1967, phased out in 1987
North Warning System (NWS) – radar, 1988-2025, Ratheon, AN/FPS-117 and short range AN/FPS-124 surveillance radars
Upgrade – As part of the United States Air Force new Arctic Strategy, their is a proposed upgrade occurring in 2025.

Others
The U.S. Navy also operates the Raytheon TPS-71 Relocatable Over-the-Horizon Radar(ROTHR)