In early 1974, a one-hour CBC TV documentary told Canadians for the first time about the existence of a secretive national agency that tapped phone calls and monitored radio signals.

Back then, the signals intelligence organization went by an unwieldy title — the Communications Branch of the National Research Council, or CBNRC.

Today it's called the Communications Security Establishment, or CSE. 

Many Canadians know far more today about the Ottawa-based cryptologic agency, due in large part to a series of stories based on documents leaked by former U.S. intelligence contractor Edward Snowden.

The spy agency officially came into existence in 1946, though the informal inception of the organization now known as the CSE happened several years earlier.

1974 CBC TV documentary on CBNRC or CSE

The Canadian government's signals intelligence agency was created in the 1940s, but the public didn't know about its existence until a 1974 CBC TV documentary. (CBC TV)

Even so, the public only learned of the agency three decades later when CBC TV aired the documentary, titled The Fifth Estate: The Espionage Establishment. (Despite the title, the piece was not produced by CBC TV's flagship investigative show the fifth estate, which would not be created until a year later.)

In the program that aired Jan. 9, 1974, CBC revealed details not only about the CBNRC, but also about the agency's close relationship with its counterpart in the United States, the National Security Agency.

It also talked about the little-known Five Eyes spying partnership among Canada, the U.S., the U.K., New Zealand and Australia, and how each country was responsible for monitoring communications in a different part of the world and then sharing findings with the group.  

Canada's signals intelligence agency, the documentary revealed, was responsible for covering polar regions and parts of Europe.

Watch the original documentary for a historical look at one of Canada's most secretive agencies.