In January 2008, four decades after the famous Tet Offensive, the secretive National Security Agency (NSA) declassified the 500-page report Spartans in Darkness , a most fascinating study on the U.S. Signals Intelligence (SIGINT) operations in Indochina, from the Japanese surrender in 1945 until the fall of Saigon in 1975.
The most interesting part of the report is, in my opinion, chapter 5 [pdf], on the highly controversial Gulf of Tonkin Incident. The author of the report, Robert J. Hanyok, shows that, contrary to Secretary of Defense Robert McNamara‘s assertions at the time, there was no attack on U.S. ships on August 4, 1964.
[ USS Maddox in 1964 - photo courtesy of the U.S. Navy ]
Note, however, that on August 2, 1964 the USS Maddox was engaged by North Vietnamese torpedo boats. In other words, the “Gulf of Tonkin Incident”, in fact, consisted of two separate incidents. An alternative version of chapter 5 is Skunks, Bogies, Silent Hounds, and the Flying Fish , released by the NSA in 2005 under the FOIA.
Also quite interesting is the study of the enemy’s Communications Intelligence (COMINT) operations in chapter 8 [pdf]. Not surprisingly, the enemy monitored (and jammed) U.S. radio communications. However, the revelation that the enemy did manage to create blue-on-blue situations by penetrating the U.S. radio communications and calling U.S. artillery / air strikes on U.S. ground units is somewhat shocking.
 Robert J. Hanyok, Spartans in Darkness: American SIGINT and the Indochina War, 1945-1975, Center for Cryptologic History, National Security Agency, 2002.
 Robert J. Hanyok, Skunks, Bogies, Silent Hounds, and the Flying Fish: the Gulf of Tonkin mystery, 2–4 August 1964 [pdf], Cryptologic Quarterly, Center for Cryptologic History, National Security Agency, 2001.
- The Gulf of Tonkin Incident, 40 years later: flawed intelligence and the decision for war in Vietnam (2004)
- Newly declassified NSA documents show analysts made “SIGINT fit the claim” of North Vietnamese attack (2005)