The Distant Early Warning (DEW) Line was the northernmost of three radar lines in Canada and Alaska.

Designed to provide enough warning time of a nuclear attack to enable launching an effective counterattack, the DEW line was placed far north of the joint Canadian-United States Pinetree Line and the Mid-Canada Line which were hampered by southerly location and migrating birds.

With construction given the highest national priority, the 63-base line reached operational status in 1957.

The Mid-Canada Line was shut down in the early 1960s, and much of the Pinetree Line was given over to civilian use.

In 1985 the United States and Canada agreed to transition the DEW line to the new North Warning System (NWS) and most of the original DEW stations were deactivated, while a small number were upgraded with all-new equipment.

Source: Wikipedia