The "Gulf of Tonkin Incident" was cited as the casus belli for the USA to commit ground forces to the war in Vietnam. It refers to 2 claimed incidents involving the naval destroyer USS Maddox on 2 and 4 August 1964 respectively, both of which are alleged to have involved unprovoked aggression against the US ship by the Vietnamese . According to an NSA investigation which was declassified in 2010, only one of the claimed incidents actually took place.  The report also reveals that the seriousness of the incident which did take place is at best questionable, in terms of a genuine casus beli for full-scale war. For example, it was the USS Maddox which fired the first (warning) shots, there were no US casualties and there were 4 North Vietnamese sailors killed and 6 wounded, with no damage to the US ship and extensive damage to three Vienamese torpedo boats. 
On August 3, US Treasury Secretary, Robert Anderson secretly recorded a call he received from Lyndon B Johnson. This provides evidence of US provocation of the attacks:
“OK. Here’s what we did. We [were] within their 12-mile limit, and that’s a matter that hasn’t been settled. But there have been some covert operations in that area that we have been carrying on – blowing up some bridges and things of that kind, roads, and so forth. So I imagine they wanted to put a stop to it. So they come out there and fire and we respond immediately with five-inch guns from the destroyer and with planes overhead. And we cripple them up – knock one of them out and cripple the other two. And then we go right back where we were with that destroyer [the Maddox], and with another one [the Turner Joy], plus plenty of planes standing by. And that’s where we are now.”
Lyndon Johnson (1964-08-03) - 
The NSA declassified and released nearly 200 documents relating to this incident in 2005 and 2006.
|Document:The Deep State and 9/11||“Many of the people who were associated with the war were looking for any excuse to initiate bombing. The sending of a destroyer up the Tonkin Gulf was primarily for provocation. ... There was a feeling that if the destroyer got into some trouble, that it would provide the provocation we needed. ”||George Ball||1977|
The Official Culprit
- ↑ a b Robert J. Hanyok, "Skunks, Bogies, Silent Hounds, and the Flying Fish: The Gulf of Tonkin Mystery, 2-4 August 1964", Cryptologic Quarterly, Winter 2000/Spring 2001 Edition, Vol. 19, No. 4 / Vol. 20, No. 1.
- ↑ Nuclear Risk
- ↑ http://www.usni.org/magazines/navalhistory/2008-02/truth-about-tonkin