The Mid-Canada Line

The Mid-Canada Line (MCL) was created between the Pinetree Line and the Distant Early Warning (DEW) Line both in geography and time. It was a chain of early-warning radar and detection sites running roughly along Canada’s 55th parallel from Hopedale, Labrador, to Dawson Creek, British Columbia. It was conceived as a tripwire to detect Soviet bombers that slipped past the more southerly Pinetree Line and to cue NORAD’s air defenses. The line reached limited operation in late 1957 and full operation on January 1, 1958¹ . It shut down in 1965 as the strategic threat shifted from manned bombers to ballistic missiles. 

Canadian and U.S. planners began formal study of a northern early-warning “fence” in February 1953. On October 8, 1953, the bilateral Military Study Group recommended a radar line near the 55th parallel; Canada agreed weeks later. Unlike the jointly funded Pinetree and DEW Lines, the RCAF would fund and operate the MCL.²

The technical concept grew from Defence Research Board work with McGill University—hence “McGill Fence.” Researchers, including J. Rennie Whitehead, demonstrated a forward-scatter/bi-static “double-Doppler” detection system using separated transmitters and receivers; any aircraft crossing the path between stations produced a distinct, easily detected beat signal. ³ Field trials along the Ottawa Valley in 1953 validated the approach and informed siting. ⁴

Cabinet approved a system organized into eight Sector Control Stations (SCS), each supervising strings of unmanned Doppler detection sites spaced tens of kilometers apart (about ninety DDS sites in all). Long-haul communications relied on tropospheric-scatter microwave links pushing data south toward the RCAF control center at North Bay. Bell Canada led major construction packages, drawing on experience from the trans-Canada microwave network. ⁵

By April 1957, western sectors were operating with RCAF crews; the complete line reached full operational status on January 1, 1958. The MCL established a Mid-Canada Identification Zone (MIDIZ) and supported “line-clearance” aerodromes just north of the fence to stage interceptors and logistics. ⁶ Sector Control Stations at Hopedale (SCS-200), Knob Lake/Schefferville (SCS-300), Great Whale River/Kuujjuarapik (SCS-400), Winisk (SCS-500), Bird (SCS-600), Cranberry Portage (SCS-700), Stoney Mountain (SCS-800), and Dawson Creek (SCS-900) supervised the unmanned strings and backhauled data via troposcatter relays such as Mount Kempis (Site 070). ⁷

The forward-scatter/bistatic technique was economical and covered large gaps, but it provided only “presence” and speed—not precise position or altitude. In practice, nuisance returns (including bird migrations) elevated the false-alarm burden, a known shortcoming of similar systems that later drove use of Doppler-filtering gap-fill radars elsewhere in the network. ⁸

As NORAD re-optimized for a missile-dominated threat and higher-performance surveillance, Canada advised in 1963 that it intended to phase out the Mid-Canada Line. The system ceased operations in 1964–65, with some western Sector Control Stations closing first (e.g., Cranberry Portage in early 1964) and the balance—including Great Whale River and Winisk—closing in April 1965. ⁹

NORAD’s official chronology records limited MCL operations by October 31, 1957, full operational status on January 1, 1958, and retirement by 1965 as the system’s contribution waned relative to newer sensors and command systems. ¹⁰

Physical remnants of the line ranged from airstrips and foundations to troposcatter pads. Several facilities found civilian afterlives—Cranberry Portage’s site became community infrastructure, and Great Whale River’s gravel runway serves Kuujjuarapik as a provincial airport. 

A more complex legacy involves environmental contamination. Many coastal and sub-Arctic sites accumulated PCBs, hydrocarbons, asbestos, and metals during Cold War operations.¹¹ Ontario’s multi-year remediation program (circa 2009–2015), supported by provincial and federal funding, targeted sixteen James/Hudson Bay sites and specific troposcatter relays (e.g., Sites 050, 060, 070). DND’s evaluation of the remediation contribution agreement details scope, timelines, and outcomes; provincial and federal environmental assessments document cleanup at individual locations. Parallel efforts proceeded in Newfoundland and Labrador¹² , Wild Boar, NL and in Nunavik/Québec under local review boards. ¹³

For historians and communities, the MCL marks a mid-century convergence of Canadian research, telecom engineering, and continental defense planning. It also illustrates the rapid obsolescence of bomber-focused warning systems in the missile era and the long tail of northern remediation. The line’s planning and operation sit squarely within Canada’s broader Cold War air-defense architecture—Pinetree to the south, DEW to the north, and NORAD at the core.