23 May 1967 – President Lyndon B. Johnson‘s administration prohibits any American air attacks within a 10-mile (16-km) radius of Hanoi.
A year earlier in June of 1966 “President Johnson served notice on North Vietnam yesterday [June 18] that the United States will ‘‘raise the cost of aggression at its source’’ by intensified use of air power. His stern warning at the White House news conference evoked speculation that the United States is now prepared to extend air attacks to oil and other supply dumps in North Vietnam. This wider air action reportedly was imminent just before the outbreak of political turmoil in South Vietnam in March.
In one of the most determined administration statements on Vietnam, Mr. Johnson expressly left open any increases in ‘‘our forces’’ and ‘‘our operations’’ in Vietnam. The president appeared intent on putting maximum military and psychological pressure on North Vietnam in the weeks ahead. He made it clear he believes this course represents the majority view in the United States. He omitted his usual assurances that the United States is risking no wider war and that it is knocking on all doors to seek negotiation.(1)
A Vietnam Archive study says that “the unannounced five‐day pause in bombing in May [1967], during which the President called upon Hanoi to accept a “political solution” in the South… “seemed to he aimed more at clearing the decks for subsequent intensified resumption than it was at evoking a reciprocal act of de-escalation by Hanoi,” the study says. Admiral Raborn in his May 6 memorandum had suggested a pause for this purpose and as an opportunity for Hanoi to make concessions with some grace.” (2)
(1) Source (New York Herald Tribune, European Edition, June 20, 1966)
(2) Source (New York Times “Vietnam Archive: Study Tells How Johnson Secretly Opened Way to Ground Combat” By Neil Sheehan, June 15, 1971