The Manhattan Project, An Interactive History Home The Manhattan Project, An Interactive History Home Department of Energy Home Office of History and Heritage Resources Home DOEHome
J.R. Oppenheimer and General Groves
Events People Places Processes Science Resources

Time Periods

Atomic Discoveries

Government Support


The Uranium
Path to
the Bomb

The Plutonium
Path to
the Bomb

Bringing It All Together

Dawn of the
Atomic Era

Postscript --
The Nuclear Age

Venona intercept regarding Theodore HallTHE VENONA INTERCEPTS
(Washington, D.C., 1946-1980)
Events > Postscript -- The Nuclear Age, 1945-Present

Soviet intelligence officers in the United States regularly communicated with their superiors in Moscow via telegraphic cables.  These messages were encrypted of course, but in 1946 the United States, with the assistance of Great Britain, began to decrypt a good number of these messages.  This program led to the eventual capture of several Soviet spies within the Manhattan Project.  The VENONA intercepts, as they were codenamed, remained a closely-guarded secret, known only to a handful of government officials, until the program was declassified in 1995.  

Meredith Gardner (left) and some of his team of cryptanalysts.

The cables should have been impossible to decrypt.  Collecting them was easy.  The United States government simply acquired copies of all cables openly sent to and from various Soviet embassies and consulates.  These messages were encrypted by a means known as a "one-time pad."  This meant that, at least in theory, decrypting them should have been impossible.  The Army's Signal Intelligence Service began working on the problem in 1943, and they gradually discovered a Soviet procedural error that allowed many of the messages to be painstakingly decrypted.  Portions of messages began to become clear in 1946, and by 1948 numerous messages were being recovered by the team led by Meredith Gardner (above left).  In 1948, Robert Lampherethe Federal Bureau of Investigation (FBI) was also brought into the investigation, its efforts led by Robert Lamphere (right). Although only messages up to 1945 were vulnerable to decryption, and these messages were several years old by that point, they still contained references to spies who had never been detected, including many who presumably continued to work for Soviet intelligence.  From 1948 to 1951, numerous Soviet spies were uncovered and prosecuted this way, including the atomic spies Klaus Fuchs (below), David Greenglass, Greenglass's handler Julius Rosenberg, and Rosenberg's wife Ethel.  Other sources, such as Theodore Hall, were detected, but without sufficient corroborating evidence other than VENONA, the government was unable to prosecute them.  (The VENONA secret was considered too valuable to reveal as evidence in an open court proceeding.)  

Klaus Fuchs's Los Alamos security badge photograph

Once messages were decrypted and translated into English, however, the identity of the individuals mentioned in them was still often not apparent.  Soviet intelligence assigned every person a unique codename and sometimes changed it.  (For example, Julius Rosenberg was ANTENNA, later changed to LIBERAL, and Theodore Hall was MLAD.)  Nonetheless, it was often possible to determine who each codename referred to based on clues within the messages.  Sometimes the message where the individual is first given a codename happens to be one of those decrypted, in which case the individual's identity is known with certainty.  In other cases, rather obvious clues make identification simple, such as when the name of ANTENNA's wife was openly given as "Ethel."  Most people were identified through follow-up investigation by the FBI based on the descriptions of their work, their lives, their appearance, and even their codename itself.  (MLAD means "youngster" in Russian; Hall was only 19 when he began his work as a spy.)  In some cases, especially when dealing with sources who were Venona intercept regarding Julius Rosenbergonly mentioned in a handful of decrypted messages, a Soviet spy's identity remains unknown to this day.

Additional wartime messages continued to be decrypted during the 1950s and beyond, but the "value added" of these decryptions gradually lessened over time.  Soviet intelligence learned of the VENONA program in 1949 through its highly-placed British agent, Kim Philby, but there was nothing they could do to stop it.  The program was finally formally terminated on October 1, 1980.

Rumors of an important codebreaking effort circulated among journalists and historians throughout the 1980s and the early 1990s, but there was no formal confirmation of the existence of VENONA until it was declassified in 1995. Today anyone who is interested can view images of the actual decrypted cables on the National Security Agency's web page at

Previous    Next

Sources and notes for this page.

The text for this page is original to the Department of Energy's Office of History and Heritage Resources.  The information for this entry is drawn primarily from the National Security Agency's web site devoted to the history of VENONA, which is available at, and John Earl Haynes and Harvey Klehr, Venona: Decoding Soviet Espionage in America (New Haven and London: Yale University Press, 1999), especially 1-22.  See also Herbert Romerstein and Eric Breindel, The Venona Secrets: Exposing Soviet Espionage and America's Traitors (Washington: Regnery Publishing, Inc., 2000), and Allen Weinstein and Alexander Vassiliev, The Haunted Wood: Soviet Espionage in America -- the Stalin Era (New York: Random House, 1999).  The Los Alamos ID Badge photograph of Klaus Fuchs was taken in 1944; it is courtesy the Los Alamos National Laboratory (LANL) and is reprinted in Rachel Fermi and Esther Samra, Picturing the Bomb: Photographs from the Secret World of the Manhattan Project (New York: Harry N. Abrams, Inc., Publishers, 1995), 106.  All of the other images on this web page are courtesy the National Security Agency.

Home | History Office | OpenNet | DOE | Privacy and Security Notices
About this Site | How to Navigate this Site | Note on Sources | Site Map | Contact Us