The Nixon administration operated a secret recording system that captured conversations in the Oval Office, Cabinet Room, Executive Office Building, Camp David and on presidential telephones. The National Archives states that the system recorded conversations from February 1971 to July 1973.
On 16 July 1973 Alexander Butterfield revealed the existence of the taping system to the Senate Watergate Committee. The Senate committee and special prosecutor then sought recordings relevant to the Watergate investigation.
Nixon resisted demands for the tapes, invoking presidential confidentiality and privilege. The resulting legal conflict culminated in United States v. Nixon. The recordings, including material relating to the Watergate cover-up, became some of the most important documentary evidence in the scandal.