Under the authority of President Lyndon B. Johnson, the United States first deployed troops to Vietnam in 1965 in response to the Gulf of Tonkin Incident of August 2 and 4, 1964. On March 8, 1965, 3,500 U.S. Marines landed near Da Nang in South Vietnam, thereby escalating the Vietnam Conflict and marking the United States' first action of the subsequent Vietnam War.
The Gulf of Tonkin Incident
During August of 1964, two separate confrontations occurred between Vietnamese and American forces in the waters of the Gulf of Tonkin that became known as the Gulf of Tonkin (or USS Maddox) Incident. Initial reports from the United States blamed North Vietnam for the incidents, but controversy has since arisen over whether or not the conflict was a deliberate act by U.S. troops to instigate a response.
The first incident occurred on August 2, 1964. Reports claim that while performing a patrol for enemy signals, the destroyer ship USS Maddox was pursued by three North Vietnamese torpedo boats from the 135th Torpedo Squadron of the Vietnam Navy. The U.S. destroyer fired three warning shots and the Vietnam fleet returned torpedo and machine gun fire. In the subsequent "sea battle," Maddox used over 280 shells. One U.S. aircraft and three Vietnam torpedo boats were damaged and four Vietnamese sailors were reported to have been killed with over six more reported as injured. The U.S. reported no casualties and the Maddox was relatively undamaged with the exception of a single bullet hole.
On August 4, 1964, a separate incident was filed wherein the National Security Agency claimed the U.S. fleet was again pursued by torpedo boats, though later reports revealed that the incident was merely a reading of false radar images and not an actual conflict. The Secretary of Defense at the time, Robert S. McNamara, admitted in a 2003 documentary entitled "The Fog of War" that the second incident never occurred.
The Gulf of Tonkin Resolution
Also known as the Southeast Asia Resolution, the Gulf of Tonkin Resolution (Public Law 88-40, Statute 78, Pg 364) was drafted by Congress in response to the two attacks on U.S. Navy ships in the Gulf of Tonkin Incident. Proposed and approved on August 7, 1964, as a joint resolution by Congress, the resolution was enacted on August 10.
The resolution carries historical significance because it authorized President Johnson to use conventional military force in Southeast Asia without officially declaring war. Specifically, it authorized the use of whatever force necessary to assist any member of the Southeast Asia Collective Defense Treaty (or Manilla Pact) of 1954.
Later, Congress under President Richard Nixon would vote to repeal the Resolution, which critics claimed gave the president a "blank check" to deploy troops and engage in foreign conflicts without officially declaring war.
The "Limited War" in Vietnam
President Johnson's plan for Vietnam hinged on keeping U.S. troops south of the demilitarized zone separating North and South Korea. In this way, the U.S. could lend aid to Southeast Asia Treaty Organization (SEATO) without getting too involved. By limiting their fight to South Vietnam, U.S. troops would not risk more lives with a ground assault on North Korea or interrupt the Viet Cong's supply path running through Cambodia and Laos.
Repealing The Gulf of Tonkin Resolution and the End of Vietnam War
It wasn't until rising opposition (and many protests) domestically in the United States and Nixon's election in 1968 that the U.S. was able to finally begin pulling troops back from the Vietnam conflict and shift control back to South Korea for war efforts. Nixon signed the Foreign Military Sales Act of January 1971 abolishing the Gulf of Tonkin Resolution.
To further limit presidential powers to make military actions without directly declaring war, Congress proposed and passed the War Powers Resolution of 1973 (despite a veto from President Nixon). The War Powers Resolution requires the President to consult Congress in any matter where the U.S. hopes to engage in hostilities or may possibly yield hostilities because of their actions abroad. The resolution is still in effect today.
The United States pulled its final troops from South Vietnam in 1973. The South Vietnam government surrendered in April 1975, and on July 2, 1976, the country officially united and became the Socialist Republic of Vietnam.