As the MCL was closed down, the early warning role passed almost entirely to the newer and more capable DEW Line farther north.

This leads to a very low-cost system that can cover huge areas, at the cost of providing no information about the precise location of the target, only its presence.

Solving this problem using the Doppler effect was a major design criterion for the AN/FPS-23 "Fluttar" that filled a similar role in the DEW line.

[1] Additionally, the Pinetree systems used pulsed radars that were fairly easy to jam and were unable to detect targets close to the ground due to "clutter."

An aircraft flying into this region would reflect some signal back towards the receiver, allowing detection at altitudes as great as 65,000 ft.[1] A major advantage of the system is that it requires much less power to operate effectively.

Willis and Griffiths speculate it might be the need for 1,000 such radars,[4] but it is also likely that the desired to locate the line further north than the heavily settled areas in southern Canada was likely significant as well.

Some preliminary tests were made in 1952 with breadboard hardware built by a graduate student, Hugh Hamilton, in order to confirm the validity of the idea.

[2] In the meantime RCA Victor had been brought in by the DRB to design and produce the receivers, transmitters and antennas for tests on a substantial scale.

All observations were transmitted to and made in the line HQ, which was set up in the equipment hut of one of the seven stations, located in Deep River.

During this time Dr. Ross Warren of RCA Victor and Dr. Whitehead jointly developed the theoretical background for the work in a major report to DRB.

[2] The Spider Web trials were followed in 1954 by intensive tests on a single 30 miles (48 km) wide link, built in the Eastern Townships by Bell Canada, who had by this time been given the go-ahead for the implementation of the Mid-Canada Line.

"[2][b] The trials on this prototype link were also conducted by Whitehead and a small team in collaboration with Air Defence Command, St. Hubert, this time on behalf of Bell.

[6] In October 1953 the MSG recommended to both governments "that there be established at the earliest practicable date, an early warning line located generally along the 55th parallel between Alaska and Newfoundland",[6] and outlined their minimum operational requirements.

One, manned by the RCAF, set out eastward from Fort Nelson, BC in order to link up with a second moving west from Flin Flon, Manitoba, while a third crewed by the Army left Lake Nipigon near Thunder Bay, Ontario for Lansdowne House about 200 kilometres (120 mi) further north.

A huge effort to map the area in a 15-mile wide strip across the entire country was started by Transport Command almost immediately, and ended by the spring of 1954.

[6] All aircraft transiting the line would have to file a flight plan through the Mid Identification Zone, or MIDIZ, centred on the fence.

[6] At about this time another huge civil engineering project was underway in Canada, the construction of a cross-Canada microwave relay telephone system.

This problem was triggered by the large flocks of migrating waterfowl during the spring and fall, which created signals so powerful that it rendered the radars useless.

[6] Although technically capable, the MCL gave little information for vectoring interceptors to their targets, so these tasks still required the Pinetree radars much farther south.

As the Soviet Union moved their offensive capability to ICBMs it became clear that both the MCL and Pinetree systems were of limited use, and the entire Mid-Canada line was shut down in April 1965.

[6] The DEW line stations were sited to provide the best possible view of the horizon, but there remained a minimum detection angle below which aircraft could sneak by without being seen.

As the MCL came online and the problem with birds became clear, the original forward-scatter concept was replaced by one using Doppler filtering to ignore anything flying below 125 miles per hour (201 km/h).