OTH

Over-the-Horizon radars, or OTHs were radar that relied on signal reflections between the ionosphere and the ground.  Signals from the transmitters were bounced back and forth between the ground and ionosphere until they reached the receiving stations.

They were used against planes, missiles, and space objects and were important in covering low areas that other radars missed.  They had a range of 900 kilometres at minimum, and 3,000 at maximum.

They were used in the United States and became active in Maine in 1988 and later the Pacific.  OTHs had issues readign northwards because of aurora borealis, which is why Canada did not end up involved in the project.

The United States Air Force used a radar and receiver on the Melville Peninsula (at Hall Beach), situated where it could see a good deal of the Arctic and a Defense Research Board receiver at Victoria Island (at Cambridge Bay) which increased this by another angle.