54 years ago today the first of two battles occurred in the Gulf of Tonkin off the coast of Vietnam.
These two battles led to the Tonkin Gulf Resolution, which gave President Johnson authorization for the use of conventional military force in Southeast Asia.  SIGINT reporting on August 5 was considered the “Smoking Gun” by the President.

A Readers Digest Version of events:

August 2:

USS Maddox (DD 731) was conducting collect intelligence mission in support of the embarked commander and higher level authorities and to assert freedom of navigation in the Gulf of Tonkin.  These patrols where known as DESOTO patrols.  While on a DESOTO patrol, the USS Maddox came under attack by three Democratic Republic of Vietnam (DRV) patrol boats.  This attack resulted in two A-4 Skyhawk fighter aircraft from the USS Ticonderoga (CV 14) attacking the three DRV boats damaging all three leaving one dead in the water.  SIGINT reporting at Phu Bai Vietnam, San Miguel, Philippines and the NSG detachment aboard the Maddox provided accurate I&W and the Marine SIGINT unit at Phu Bai, Vietnam issued a CRITIC which alerted all relevant command, including the Maddox.

August 3:

The Phu Bai unit misinterpreted search and salvage operation by the DRV as a potentially dangerous concentration of enemy boats and issued a second CRITIC.  This report set the U.S. Navy on high alert.  By mid-morning the USS Maddox and USS Turner Joy (DD 951) was heading towards their patrol station, which near Hon Me Island.  Almost as soon as the two destroyers arrived on statin in early afternoon, they were shadowed by a DRV patrol boat.

August 4/5:

While on station the USS Maddox received a CRITIC from Phu Bai, which stated, POSS DRV NAVAL OPERATIONS PLANNED AGAINST THE DESOTO PATROL TONIGT 04 AUG. AMPLIFYING DATA FOL.”  Twenty-five minutes later, Phu Bai issued a follow-up report at which reported, ‘IMMINENT PLANS OF DRV NAVAL ACTION POSSIBLY AGAINST DESOTO MISSION.”  Shortly after this report the Maddox reported that it had detected two surface contacts and three air contacts on its radar.  However, at the time the ship’s radar was malfunctioning and had a difficult time holding RADAR contact.  As they continued operations these radars started generate several false contacts and then the contact would drop out.  It was during this time of confusion the two destroys gyrated wildly in the dark waters and the Turner Joy fired over 300 rounds from their 5 inch Mk 42 guns.

The DESOTO mission did not have any supporting SIGINT to indicate an attack was imminent.  San Miguel reported via a SPOT report at priority that DRV was conducting a salvage operation and that the DRV never attacked, nor planned to attack either ship.

Here is the declassified report:

Skunks, Bogies, Silent Hounds, and the Flying Fish: The Gulf of Tonkin Mystery, 2-4 August 1964