Here is the beginning of the hearing on the National Security Agency held by the Church Committee which occurred on October 29th, 1975. The Chairman was Frank Church, a Democratic senator from Idaho who had presidential aspirations. He makes it clear at the outset that, at the time, the NSA was so secretive that almost no Americans had ever heard of it, despite its huge employee base and enormous budget. It had no statutory basis and no oversight.
Americans really should familiarize themselves with this history.