What did the declassified documents reveal?

Declassified: American Cryptology During the Korean War This is a declassified National Security Agency record, released through The Black Vault, detailing the state of American cryptology during the Korean War. The document was written by Dr. Thomas R. Johnson, a 35-year veteran of cryptology operations, and is unclassified in its entirety. The document was released in July 2001, as part of a larger declassification effort by the NSA. The agency has recently declassified a few historical summaries related to the Korean War, but has not yet begun to release any reports from the war itself. American Cryptology During the Korean War With Korean war cryptology, we are still in the early stage of declassification fifty years after the outbreak of the war. 99 Dr. Thomas R. Johnson is a 35-year veteran of cryptology operations, Currently associated with CIA's Center for the Study of Intelligence, he is the author of a classified four-volume history of American cryptology during the Cold War. The Korean War was a significant conflict that began on June 25, 1950, when North Korean forces invaded South Korea. In response to a United Nations call for troops to restore peace, the United States committed ground, air, and naval forces to the conflict. The war ultimately ended with an armistice signed on July 27, 1953, which provided for the continued presence of US troops on Korean soil. The United States suffered more than 140,000 casualties during the engagement. A peace treaty has never been signed, and Allied silence about the role of cryptology in World War II was broken in 1974 by the publication of Frederick Winterbotham's The Ultra Secret. The world had waited almost 30 years for the beginning of a declassification program for World War II communications intelligence. A few spare historical accounts written during and immediately after the war represented most of what the National Security Agency and the UK Government Communications Headquarters had been willing to divulge. With Korean war cryptology, we are still in the early stage of declassification fifty years after the outbreak of the war. NSA has recently declassified a few historical summaries, but has not yet begun to release any reports from the war itself. So what do we know about cryptology in Korea? Some of our knowledge preceded the official declassification effort. When Clay Blair wrote his history of the Korean war in the 1980s, he incorporated some tantalizing bits and pieces about the role of exploited North Korean messages, especially as it related to the Pusan perimeter. More recently, researcher Matthew Aid has written about the role of US human and signals intelligence in the Korean War. Aid's work has shed light on the importance of cryptology during the conflict. The Korean War can best be understood in terms of World War II, which has been described as a "SIGINT War." By the end of the war, the Americans and British, with help from the Canadians and Australians, were able to…

Why was this case declassified?

This material entered the public record through the U.S. declassification and Freedom of Information Act (FOIA) process. The originating source document is linked on this page so the citation chain is auditable.

NSA American Cryptology During The Korean War This Is A Declassified National

◆ BLUF — The short version

Declassified: American Cryptology During the Korean War This is a declassified National Security Agency record, released through The Black Vault, detailing the state of American cryptology during the Korean War. The document was written by Dr. Thomas R. Johnson, a 35-year veteran of cryptology operations, and is unclassified in its entirety.

Date: AUG 1 · 2026
Release: Declassified · U.S. public record (FOIA)
Source document: View the primary source document

↯ Dispatch — press play3:01

0:003:01

↯ Share

X in r/

Episode notes

View the primary source document

Questions about this case

What was NSA American Cryptology During The Korean War This Is A Declassified National about?: Declassified: American Cryptology During the Korean War This is a declassified National Security Agency record, released through The Black Vault, detailing the state of American cryptology during the Korean War. The document was written by Dr. Thomas R. Johnson, a 35-year veteran of cryptology operations, and is unclassified in its entirety.
Why was this case declassified?: This material entered the public record through the U.S. declassification and Freedom of Information Act (FOIA) process. Storyflo narrates it directly from the public release.

intelligence-vault

Related cases

✉ Dispatches

A short dispatch when a new file is released — narrated, answer-first, and linked straight to the primary source. No spam; unsubscribe anytime.

↯ Subscribe to the feed

RSS feed Browse all cases

NSA American Cryptology During The Korean War This Is A Declassified National

Questions about this case

Related cases

CIA Intelligence Memorandum Concerning The Chinese Communist Response To G R C

From The Declassified Archives, This Is A Central Intelligence Agency

CIA Requirements For Photo Reconnaissance Of China Mainland

Today, We Examine A Central Intelligence Agency Record From September

CIA C I A Record Concerning Probable Communist Reactions To Certain S E A T O

Questions about this case

Related cases

CIA Intelligence Memorandum Concerning The Chinese Communist Response To G R C

From The Declassified Archives, This Is A Central Intelligence Agency

CIA Requirements For Photo Reconnaissance Of China Mainland

Today, We Examine A Central Intelligence Agency Record From September

CIA C I A Record Concerning Probable Communist Reactions To Certain S E A T O

Get the next declassified case in your inbox