In 1949, the United States Congress agreed to 'shared' financing the construction of a line of radar stations, across southern Canada, to enhance warning of ‘air attack’ and for the direction of fighter interceptors.

In the Eastern Canada, the stations ran in a line essentially along the 50th parallel, St Sylvestre being an anomaly situated at 46.33 Degrees North.

[8] Amongst several reasons, the St Sylvestre radomes on Mont Sainte-Marguerite, at an altitude of 698 metres (2290 feet),[9] on the north edge of the Appalachians, easily covered the critical approaches into the eastern United States.

Recurring wind damage, and winter weather, led to the housing of the radars inside 15-metre diameter inflated rubber domes.

[24][25] The Main Building radars were supported by sites on two adjacent hills designated RX (Receiver) on Mont 'Handkerchief' and TX (Emitter).

O'Connell Company (Montreal),[27] like all PINETREE Line stations, St Sylvestre was a self-contained community, with sixty ‘private married quarters’, initially five single and fifty-five double-width (single and two story) family homes,[28] with 30 PMQs added in 1961, in a mobile home park, accommodating growth at the Station.

There were separate buildings for two primary schools: (Hillside Schools - Innobis Confidimus: In Us Trust), a recreation centre with a bowling alley, theatre, gymnasium and swimming pool (No.8), a ‘twinned two denomination’ chapel (No.17),[30] the sports fields, an outdoor skating rink, a 25-yard shooting range and a single line ski tow.

[31] Supporting the ‘Main Building’ operations 'up' on Mont Ste Marguerite, was the Station Headquarters’ Administration Building (No.16), and its parade square, a one-bay fire hall (No.60), the station medical/dental hospital, a water treatment, the reservoir and distribution facility, a central heating plant, construction engineering, supply and mobile equipment shops (No.18), and the guard house, at the front entry.

The conversion to the ‘automated’ SAGE system terminated the use of these ‘auxiliary volunteers’ - as they were trained exclusively for manual detection and intercept operations.

[35] In May 1962, the SAGE Annex and two Ground Air Transmit Receive (GATR) Towers: ‘TX’ to the south, and ‘RX’ to the southeast, for vectoring manned interceptors, were completed.