The Center of Military History (CMH) has publications, series, and collections on the Vietnam War available online. To search for additional documents beyond those included below, try the Vietnam War General Resources (take a look at General References and Archival Material) and The Vietnam War 50th Commemoration online exhibit.
Airmobility, 1961-1971 (CMH Pub 90-4)
Allied Participation in Vietnam (CMH Pub 90-5)
Base Development in South Vietnam, 1965-1970 (CMH Pub 90-6)
Cedar Falls-Junction City: A Turning Point (CMH Pub 90-7)
Command and Control, 1950-1969 (CMH Pub 90-8)
Communications-Electronics, 1962-1970 (CMH Pub 90-9)
Development and Training of the S. Vietnamese Army, 1950-1972 (CMH Pub 90-10-1)
Division-Level Communications, 1962-1973 (CMH Pub 90-11)
Dust Off: Army Aeromedical Evacuation in Vietnam (CMH Pub 90-28)
Field Artillery, 1954-1973 (CMH Pub 90-12)
The Final Collapse (CMH Pub 90-26)
Financial Management of the Vietnam Conflict, 1962-1972 (CMH Pub 90-13)
Judge Advocates in Combat: Army Lawyers...Vietnam to Haiti (CMH Pub 70-77)
Law at War: Vietnam, 1964-1973 (CMH Pub 90-14)
Logistics Support (CMH Pub 90-15)
MACV: The Joint Command in the Years of Escalation, 1962-1967 (CMH Pub 91-6)
MACV: The Joint Command in the Years of Withdrawal, 1968-1973 (CMH Pub 91-7)
Medical Support of the U.S. Army in Vietnam, 1965-1970 (CMH Pub 90-16)
Modern Volunteer Army Program: Benning Experiment, 1970-1972 (CMH Pub 90-2)
Mounted Combat in Vietnam (CMH Pub 90-17-1)
Reorganizing for Pacification Support (CMH Pub 90-27)
Riverine Operations, 1966-1969 (CMH Pub 90-18)
The Role of Military Intelligence, 1965-1967 (CMH Pub 90-19)
Seven Firefights in Vietnam (CMH Pub 70-4)
Sharpening the Combat Edge: Use of Analysis...Military Judgment (CMH Pub 90-20)
Tactical and Material Innovations (CMH Pub 90-21)
The U.S. Army Before Vietnam, 1953-1965 (CMH Pub 76-3)
U.S. Army Engineers, 1965-1970 (CMH Pub 90-22)
U.S. Army Special Forces, 1961-1971 (CMH Pub 90-23-1)
Vietnam From Cease-Fire to Capitulation (CMH Pub 90-29-1)
The War in the Northern Provinces, 1966-1968 (CMH Pub 90-24)