On August 7th 1964 the United States Congress passed the Gulf of Tonkin Resolution, which authorised President Lyndon Johnson to utilise military force in Vietnam:

“To promote the maintenance of international peace and security in south-east Asia…

Whereas naval units of the communist regime in Vietnam, in violation of the principles of the Charter of the United Nations and of international law, have deliberately and repeatedly attacked United States naval vessels lawfully present in international waters, and have thereby created a serious threat to international peace…

Whereas these attacks are part of a deliberate and systematic campaign of aggression that the communist regime in North Vietnam has been waging against its neighbours and the nations joined with them in the collective defence of their freedom…

Whereas the United States is assisting the peoples of south-east Asia to protect their freedom, and has no territorial, military or political ambitions in that area, but desires only that these people should be left in peace to work out their own destinies in their own way…

It is resolved by the Senate and House of Representatives of the United States of America in Congress assembled:

1. That the Congress approves and supports the determination of the President as commander in chief, to take all necessary measures to repel any armed attack against the forces of the United States and to prevent further aggression.

2. The United States regards as vital to its national interest, and to world peace, the maintenance of international peace and security in Southeast Asia. Consonant with the Constitution of the United States and the Charter of the United Nations and in accordance with its obligations under the Southeast Asia Collective Defence Treaty, the United States is therefore prepared, as the President determines, to take all necessary steps, including the use of armed force, to assist any member or protocol state of the Southeast Asia Collective Defence Treaty requesting assistance in defence of its freedom.

3. This resolution shall expire when the President shall determine that the peace and security of the area is reasonably assured by international conditions created by action of the United Nations or otherwise, except that it may be terminated earlier by concurrent resolution of the Congress.”