11 June 1965: Relocation of HYDRA Relay and Radio Centre Operating Personnel

A month later, Finch was even less optimistic, putting the cutover date at April 1, 1966.  

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Fixed Communications - Hydra Telegraph Relay System - Relocation of Hydra - Plans and Policy, RG24, S-2723-2, Vol. 1, Library and Archives Canada (LAC)

1961-1966: “In Event of an Emergency”: HYDRA Goes to Ground
Planning Runs into Difficulties
11 June 1965: Relocation of HYDRA Relay and Radio Centre Operating Personnel