Harvard Library defines primary sources as:
"Primary sources provide first-hand testimony or direct evidence concerning a topic under investigation. They are created by witnesses or recorders who experienced the events or conditions being documented.
Often these sources are created at the time when the events or conditions are occurring, but primary sources can also include autobiographies, memoirs, and oral histories recorded later.
Primary sources are characterized by their content, regardless of the format available. (Handwritten notes could be published; the published book might be digitized or put on microfilm, but those notes are still primary sources in any format).
Some types of primary sources:
Wait, why can't I just Google for primary sources?
You absolutely could, but one of the advantages of searching through a curated collection of primary sources if you know right away that everything there is a primary source, that the information is reliable enough, and often the content may not be indexed by Google (making it irretrievable in a Google search).
The collection is the most comprehensive compilation of declassified documents from the executive branch. The types of materials include intelligence studies, policy papers, diplomatic correspondence, cabinet meeting minutes, briefing materials, and domestic surveillance and military reports. The collection editors have actively monitored the release of formerly classified documents from presidential libraries. They have also added numerous major releases of declassified documents from the Department of State, Department of Defense, Central Intelligence Agency, Federal Bureau of Investigation, Joint Chiefs of Staff, and other executive agencies.
From the award-winning, nongovernmental National Security Archive, this resource consists of expertly curated, and meticulously indexed, declassified government documents covering U.S. policy toward critical world events – including their military, intelligence, diplomatic and human rights dimensions – from 1945 to the present. Each collection is assembled by foreign policy experts and features chronologies, glossaries, bibliographies, and scholarly overviews to provide unparalleled access to the defining international issues of our time.
Founded in 1985 to check rising government secrecy, the National Security Archive is an investigative journalism center, open government advocate, international affairs research institute, and is the largest repository of declassified U.S. documents outside the federal government. (This is a direct link to the same content which ProQuest has indexed as Digital National Security Archive)
The Digital Archive contains once-secret documents from governments all across the globe, uncovering new sources and providing fresh insights into the history of international relations and diplomacy. The Digital Archive is overseen by the Wilson Center's History and Public Policy Program and focuses on the interrelated histories of the Cold War, Korea, and Nuclear Proliferation.
Vietnam War specific collections include:
Sampling of primary documents showing CIA's involvement in every aspect of the Indochina War. (George Washington Univ.)
The AAD's Vietnam War portal is a curated collection of NARA records specific to the Vietnam War. Information on honors awarded to soldiers, casualties, military units, combat incidents and more are available.
The Vietnam Center and Sam Johnson Vietnam Archive (Texas Tech University) collects and preserves the documentary record of the Vietnam War, and supports and encourages research and education regarding all aspects of the American Vietnam Experience.
This collection includes:
Though the Office of the Historian recommends students primarily look at the Nixon and Ford Administrations, you have access to a much broader range of sources. Depending on your topic and the affected time period, you may want to look over the other administrations whose terms were contemporaneous with the Vietnam War.
The Pentagon Papers, officially titled "Report of the Office of the Secretary of Defense Vietnam Task Force", was commissioned by Secretary of Defense Robert McNamara in 1967. In June of 1971, small portions of the report were leaked to the press and widely distributed. However, the publications of the report that resulted from these leaks were incomplete and suffered from many quality issues.
On the 40th anniversary of the leak to the press, the National Archives, along with the Kennedy, Johnson, and Nixon Presidential Libraries, has released the complete report. There are 48 boxes and approximately 7,000 declassified pages. Approximately 34% of the report is available for the first time. The National Archives & Records Administration has made this available without redaction and included supporting materials.
This resource, from the Office of the Director of National Intelligence, is not easy to use, but contains declassified documents from the Central Intelligence Agency, the Defense Intelligence Agency, the National Geospatial-Intelligence Agency, and the National Security Agency. The documents are not searchable, but can be browsed and read in full either on the site or downloaded.
Famous Trials, a site by Dr. Douglas O. Linder (University of Missouri-Kansas City School of Law), contains links to many primary documents, but the page itself is a secondary source. If your research project is on My Lai or the courts-martial, you may want to go here to get background information before searching for other primary sources.
Declassified documents related to the Gulf of Tonkin incident in 1964. (National Security Agency, NSA)