To counter the threat of Soviet bombers flying over the Arctic, the U.S. and Canada developed the DEW Line. Other examples (Pinetree Line) have since been built with even better performance. An alternative early warning design was the Mid-Canada Line, which provided "line breaking" indication across the middle of Canada, with no provision to identify the target's exact location or direction of travel. Starting in the 1950s, a number of over-the-horizon radars were developed that greatly extended detection ranges, generally by bouncing the signal off the ionosphere. Modern day Today the early warning role has been supplanted to a large degree by airborne early warning platforms. By placing the radar on an aircraft, the line-of-sight to the horizon is greatly extended. This allows the radar to use high-frequency signals, offering high resolution, while still offering long range. A major exception to this rule are radars intended to warn of ballistic missile attacks, like BMEWS, as the high-altitude exo-atmospheric trajectory of these weapons allows them to be seen at great ranges even from ground-based radars. Early systems Chain Home Chain Home Low SCR-270 AN/CPS-1 CXAM radar Freya radar 1950s through 70s Pinetree Line Mid-Canada Line Distant Early Warning Line Duga radar BMEWS AMES Type 80 AMES Type 84 AMES Type 85 ROTOR Dnestr radar Dnepr radar Daryal radar Linesman/Mediator Operational systems AWACS Daryal radar Dnestr radar Don-2N radar Dunay radar GIRAFFE EL/M-2080 Green Pine EL/M-2090 Erieye Jindalee Long Range Discrimination Radar North Warning System PAVE PAWS Red Color Sea-based X-band Radar Voronezh radar References Radar Early warning systems