The Central Intelligence Agency has released a newly
declassified version of its closely-held internal history of
the Berlin Tunnel Operation, which was an effort in the
mid-1950s to tap into Soviet communications through a tunnel
constructed in the Soviet sector of Berlin. The operation was
famously compromised by a Soviet mole in British intelligence
before it even began.

The official CIA history of the operation was prepared in 1968
and published -- in two copies. A declassified version was
finally approved for release in February 2007.

See "Clandestine Services History: The Berlin Tunnel Operation,
1952-1956," 24 June 1968:

http://www.fas.org

CIA internal histories are a largely untapped resource since
the Agency has been slow to declassify and release them.

A previously published CIA account of the Berlin Tunnel
operation, which includes links to excerpts from other
internal histories of the episode, is here:

https://www.cia.gov

A clandestine services history of the 1953 coup in Iran was
leaked to the New York Times in 2000, after the CIA refused to
declassify it. The document is available from the National
Security Archive here:

http://www.gwu.edu/