Lesson Plans: Grades 9-12

The Gulf of Tonkin Resolution and Escalation of the Vietnam War

A We The People Resource
Created March 31, 2011


The Lesson


Gulf of Tonkin: N. Vietnamese Gunboat

Photograph taken from USS Maddox (DD-731) during her engagement with three North Vietnamese motor torpedo boats in the Gulf of Tonkin, 2 August 1964. The view shows one of the boats racing by, with what appears to be smoke from Maddox' shells in its wake.

Credit: Courtesy of the U.S. Naval Historical Center

"On the first attack, the evidence would be pretty good. On the second one the amount of evidence we have today is less than we had yesterday. This resulted primarily from correlating bits and pieces of information eliminating double counting and mistaken signals. This much seemed certain: There was an attack. How many PT boats were involved, how many torpedoes were fired, etc. - all this was still somewhat uncertain. This matter may be of some importance since Hanoi has denied making the second attack." – National Security Advisor McGeorge Bundy, at the White House staff meeting at 8 a.m. on August 5, 1964, discussing the Gulf of Tonkin incident.

"I believe that within the next century, future generations will look with dismay and great disappointment upon a Congress which is now about to make such a historic mistake." – Senator Wayne Morse, during the Senate debate of the Gulf of Tonkin Resolution, August 6-7, 1964

In August 1964, a small military engagement off the coast of North Vietnam helped escalate the involvement of the United States in Vietnam; the Vietnam War would become the longest military engagement in American history prior to the Iraq and Afghanistan wars. Many historians now agree that the Gulf of Tonkin incident, in which many believed North Vietnamese ships had attacked American naval forces, may not have occurred in the way it was described at the time. The decisions made by President Lyndon B. Johnson and his top advisors, and the Congressional debate that ensued, resulted in a resolution giving LBJ authority to pursue a military policy in Vietnam that many people have come to believe was flawed and misguided. 

This lesson raises a number of questions relating to the Gulf of Tonkin incident and subsequent decisions.  How important was flawed, manipulated, or disregarded intelligence in the American decision to escalate our military involvement in Vietnam following the Gulf of Tonkin incident in August 1964? Did American officials, including President Johnson and Secretary of Defense Robert McNamara, intentionally manipulate the information they were receiving to reach the conclusion they wanted? What does historical hindsight teach us about this one specific event and, more broadly, about presidential decision-making in times of crisis? What lessons can be learned that have bearing on current and future policies?

Guiding Questions

  • What were the factors that led to Congressional action authorizing military force in the Gulf of Tonkin incident?
  • By studying this incident and the debate it has generated, what can we learn about twentieth century American democracy and military affairs?

Learning Objectives

After completing this lesson, students should be able to do the following:

  • Explain the chronology of events in the Tonkin Gulf incident in1964.
  • Evaluate the decisions made by the Johnson Administration that led to their request for the Gulf of Tonkin Resolution.
  • Explain the major thrust of the Senate debate on the Gulf of Tonkin Resolution and why this measure passed with overwhelming support.
  • Analyze documents from the time to help students reach their own interpretation about these events and their significance.
  • Understand the process by which historians use declassified materials to understand how interpretations of events need to be modified.

Use the Tonkin Gulf incident to explore connections between the military, intelligence, Executive and Congressional branches in modern foreign affairs.


On August 4, 1964, President Lyndon Johnson announced that the North Vietnamese had attacked U.S. ships in the Gulf of Tonkin. Johnson sent airplanes against the North Vietnamese and asked Congress for a resolution that supported his actions. Congress authorized the President to take “all necessary measures to repel any armed attack against the forces of the United States and to prevent further aggression” in the Tonkin Gulf Resolution. The vote in the Senate on August 7 was 88-2 with only Senators Wayne Morse and Ernest Gruening opposing the joint resolution “to promote the maintenance of international peace and security in southeast Asia.”

The Tonkin Gulf Resolution gave the President authority “to take all necessary measures” to oppose any armed attack upon the United States; President Johnson and President Nixon relied upon the resolution as the legal basis for their Vietnam military policies. Yet 40 years after the incident, evidence now available reveals that the Johnson administration may have misled the public and Congress about the nature of the Tonkin incident.

The details of the debate around the Tonkin Gulf Resolution reveal that some of the senators accepted Cold War theories of the domino effect and containment, which may have limited their ability to consider a range of responses to the incident. A great deal of information about the Tonkin incident has become readily available to scholars and the public in the past few years. This makes it possible for Americans and others to gain access and attempt to formulate their own opinions.

Finally, former military intelligence official R. A. Mackinnon, an advisor on Southeast Asia in 1965, wrote a comprehensive review of the intelligence on the Gulf of Tonkin. This document totals 111 pages, but reading the first few pages of the Introduction gives the reader a sense for the officials’ own criticism and scrutiny of the Tonkin incident and its use by the Johnson administration. The document is available on the National Security Agency’s website.

Preparation Instructions

To prepare to teach this lesson, download or bookmark the following EDSITEment websites:

Bookmark a segment of the Senate debate.

Lesson Activities

Activity 1. Domestic vs. Military Considerations

Step One:

Students should read or listen to LBJ’s two conversations with Robert McNamara from August 3, 1964, available as Clip 1 and Clip 2 of "LBJ Tapes on the Gulf of Tonkin Incident." The clips are in .wma format, and so running the audio will require Windows.

These conversations reveal the convergence of military and domestic considerations for the President and his Secretary of Defense. Students should write short quotations from the text which demonstrate the connection of domestic political concerns with military actions, then follow each quote with their commentary on how it illustrates this theme

Step Two

To explore this theme further, students should analyze the series of four conversations (Clips 3 through 6) from August 4, 1963, in which LBJ and McNamara discussed and analyzed the second series of alleged attacks. But were these actual attacks? Many historians (as well as McNamara himself) have cast doubt on this question. Ask students to  comment on a variety of possible issues: confusion on the part of the administration; LBJ’s domestic political concerns; and specific issues or details where historians now believe the information was wrong (students would have some background on this from the introductory remarks to each section of the telephone conversations). Teachers can decide to split students into groups, and have each one focus on a specific theme from above, and then report back to the class as a whole.

Activity 2. What’s Important Here?

Next, students should read the text of the August 5, 1964, White House staff meeting (available as a .pdf file) to begin to analyze the military and political intelligence overlap that is so important in the Tonkin Gulf incident. Noting answers on paper, students will comment on three key aspects of this document:

  • Do the participants in the meeting think the evidence is clear and convincing that the North Vietnamese have attacked the American ships?
  • What reservations are advanced by Cater? How does Bundy respond to them?
  • What is Bundy’s attitude about Congress’ involvement in this issue?
  • What does this indicate about the relationship between the Executive branch and Legislative branch on foreign policy issues at that time?
  • What does the Constitution say about the Executive and Legislative branch in foreign affairs? What, in your (student’s) opinion, is the most important piece of information from these minutes? Explain your choice.

Teachers may find the following definitions helpful in preparing for this lesson; they can determine how to share with their students:

  • DRV – Democratic Republic of Vietnam (North Vietnam)
  • ChiComs – The People’s Republic of China (Communist China)
  • USIA – United States Information Agency

W.Y.S. – William Y. Smith (initials at end), staff member of the National Security Council, working for McGeorge Bundy

Activity 3. LBJ’s Rationale and the Dissenters

Finally, students should analyze President Johnson’s Message to Congress of August 5, 1964, presenting the case for a Congressional commitment to military action in Southeast Asia; a small part of the Senate debate on it (focusing on Senators Morse and Gruening’s dissents); and the resolution itself. On LBJ’s speech, students should examine two topics: LBJ’s use of recently received intelligence  (using the knowledge they gained in the earlier activity using the phone calls) AND the President’s overall foreign-policy concerns in this matter. In analyzing the debate, students should discuss the two dissenters’ main concerns. Finally, they should discuss the Congressional resolution to highlight the sections that indicate Congress’ acceptance of LBJ’s rationale, as well as those that reflect Cold War politics and ideals.



  • Students engage in a simulation of the Tonkin Gulf Resolution debate, using the information that is now available – which was not disclosed then – that they have been examining. The goal would be to help them see how differently the debate might have unfolded, if the intelligence had been fully disclosed.
  • Students write an op-ed piece for August 8, 2004, on the 40th anniversary of the Gulf of Tonkin resolution. They are asked to reflect on why the original measure was passed and whether they now think the measure was justified, given the information that has come to light.

Extending The Lesson

1. Historical context and hindsight: Students can analyze the evolution of Walter Cronkite’s views on this issue, by listening to Cronkite’s discussion of the Gulf of Tonkin incident and its aftermath, which offers a good assessment of what was known then and now. (Note: this audio clip is nearly 13 minutes.) This clip is linked from the Internet Public Library, an EDSITEment-reviewed website.

Students could analyze part of an article by National Security Agency historian Robert J. Hanyok on military intelligence and the Tonkin Gulf, which confirms what some historians have long argued: that there was no second attack on U.S. ships in Tonkin on August 4, 1964. The document is long, but teachers could decide what portions they want to use with their students. This document is from the National Security Archive, linked to the EDSITEment-reviewed History Matters site.

2. Going to War: Students could compare and contrast LBJ’s speech to Congress on the Tonkin Gulf incident with those of other presidents seeking Congressional support for war:

William McKinley's request for Congressional approval of his declaration of war against Spain, April 5, 1898, is available from The Spanish American War Centennial Website. This site is linked to American Memory, an EDSITEment-reviewed site.

Selected EDSITEment Websites

American Memory

The Avalon Project at Yale Law School

National Archives Education

National Security Archive

Internet Public Library

New Perspectives on the West

The Basics

Grade Level


Subject Areas
  • History and Social Studies > U.S. > AP US History
  • History and Social Studies > World > The Modern World (1500 CE-Present)
  • History and Social Studies > Place > Asia
  • History and Social Studies > U.S. > Postwar United States (1945 to early 1970s)
  • History and Social Studies > Themes > War and Foreign Policy
  • Critical thinking
  • Debate
  • Gathering, classifying and interpreting written, oral and visual information
  • Historical analysis
  • Map Skills
  • Using primary sources



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