Plans for what would become the Pinetree Line were underway as early as 1946 within the Permanent Joint Board on Defense (PJBD), a Canadian-U.S. organization.

However, the costs of running such a system in the post-war era was too high, and instead Canada concentrated on the areas around Ontario and Quebec, while the United States set up stations in the Midwest and along the eastern seaboard.

In 1949 Congress agreed to a $161 million construction program in co-operation with the RCAF, for a continuous line of stations across southern Canada.

Studies were already underway in 1951 to build a series of Doppler bistatic radar stations somewhat farther north, which would develop into the Mid-Canada Line.

The Pinetree stations were kept operational during this period, and most underwent modifications as a part of the deployment of the Semi-Automatic Ground Environment (SAGE).