During a nationally televised address from the White House, on this day in 1974, President Nixon announced that he was going to release the White House tapes to the House Judiciary Committee which subpoenaed the tapes of 42 White House conversations.
In February 1971, Nixon ordered the installation of a recording system in several different sections of the White House. The President secretly recorded his conversations with administration officials, staff, and even with members of his family. The existence of the White House tapes was made public by White House aide Alexander Butterfield during a televised testimony to the House Committee in July, 1973.
One of those tapes later became known as the "smoking gun", in which Nixon (obstructing justice) ordered the FBI to end its investigation of the Watergate break-in. This recording proved Nixon's guilt and attempt to cover-up the scandal. A few months later, on August 8, 1974, President Nixon resigned from office.
Watch Nixon announce the release of the White House tapes in this video from the Nixon Library: