Short : 12 months:
"Tour of duty" means how much time did a person typically spend in a war zone. In Vietnam, the "war zone" was complicated. For 99% of Army and Marine ground soldiers, the war zone was limited to South Vietnam. But for Air Force and Navy pilots, the "war zone" extended beyond South Vietnam to North Vietnam, Cambodia and Laos. (Carrier fighter pilot John McCain, for example, a bona fide hero for his prison time in North Vietnam, never set foot in the South Vietnam combat zone, never witnessed ground forces in battle. Also, many Air Force flight missions in Southeast Asia were flown out of Guam.)
So, recognizing some variances, it's easiest to consider ground soldiers of the Army and Marine Corps. Since all of South Vietnam was a combat zone, the key factor was time "in-country" -- that period between boots first stepping down on the tarmac to "wheels-up" at the end of a tour. But that in-country period did not translate directly into "combat time", which was more accurately a factor of one's military service and specialty; only about half of those who served in Vietnam were routinely exposed to the dangers of combat.
For most of its personnel as the steady build-up progressed, Army eventually established the in-country tour length at 12 months. This required tour length applied to both enlisted men and commissioned officers, and equally to Regular, Reserve and National Guard soldiers. The Marines were required to serve 6-month tours, but were given incentives to serve for 13-months; most did.
But the Army and Marine Corps also had programs where, if you were willing to extend your tour an additional 6 months, they would give you a free leave of 30 days in between the two tours, flying you anywhere you wanted to spend it free of charge. The flight time didn't count towards those thirty days, nor was the leave time credited towards your extra 6 months. The same applied to each successive six-month extension. These extension programs were usually more popular among headquarters administrative personnel or people who spent their entire tours on really huge fortified and very well-defended bases, than they were among infantrymen. Overly frequent rotation of forces is counter-productive and frequent rotation of forces is expensive; the objective was to find some middle ground between the wishes of the men and the requirements of the military mission. (By comparison, World War II soldiers served for the duration of the war, or until becoming casualties precluding a return to duty.)
(Some Army and Navy special operations personnel such as Special Forces and SEALs served six month TDY tours (temporary duty, with different pay schedules) in country in succession. That is, a "green beret" might be on his "sixth straight tour", which meant that he had been in country for three straight years.)
It's important to note that in Vietnam the Army rotated personnel, not units. The unit (i.e., an Army brigade, Marine battalion) was permanently based in-country, and individual soldiers were rotated in and out of country to and from that unit. (Today both services try to follow the traditional British regimental example. That is, both Army and Marines now try to rotate whole units, usually whole brigades, keeping members together as a cohesive unit from beginning to end of a combat tour in-country. This more expensive practice largely negates the possibility of individual tour extensions, but does significantly improve overall unit effectiveness.) For a deadly war that dragged on year after year, the practice of rotating individuals was not the best for unit morale, cohesion and effectiveness, but it was more cost effective. Still, until the Draft ended in 1975, ground soldiers were widely considered, even in the military, as just more mechanical widgets in the grand scheme of things, to be plugged in like interchangeable nuts and bolts where and when needed. (There remains among certain naive or arrogant civilian quarters a continued tendency to view soldiers in such a demeaning manner, through talk of inanimate "troops", etc., even though, in a modern all-volunteer military, 80% of American citizens in their age group cannot qualify for service in today's rather well compensated Regular Army. It's a very different military force today.)
Combat units in Vietnam tried to follow as best they could a practice of not committing personnel or small units to constant combat situations for longer than six months. So a man or his squad ideally might be deployed "out in the boonies" for six months before being pulled back to headquarters base camp for the remaining six months of his one-year tour. But, due to constant high casualties and inherent mission requirements, it rarely worked out so neatly. (Greatly improved body armor and improved medical capabilities today result in far fewer disabling injuries and deaths from wounds than was the case in Vietnam; this naturally results in significantly less personnel turn-over today.) In Vietnam you simply never wanted to send out a "green" squad for six months with no experienced personnel in it. And employing soldiers in static defense at base camp or around a civilian town certainly did not ensure that they would not come under deadly attack.
For ground combat personnel like Army infantry and Marines, where casualties were highest (in Vietnam 92%, today 98%), the limited year-long tours were a mixed blessing. As was the practice in all American wars up to 1975, most combat ground soldiers during the Vietnam era were involuntarily drafted, very young, single men, and the limit on tour lengths in Vietnam helped ensure that they would not be dumped into endless war and forgotten. After all, regardless of what credentials they bought to the table, and very many of them had undergraduate and graduate degrees, their "grateful nation" felt that their lives were worth a basic pay of only $2.00 for each day they managed to survive in-country.
On the other hand, the one-year tours also gave rise to a situation where almost half of American combat forces in theater were always rather new and inexperienced individual soldiers, while their enemy, who kept going at it as a small unit year after year, grew ever more expert and effective at his job for as long as he remained alive - on his own turf. This had an inherent propensity to raise US casualties.
So, for US combat personnel such as infantry, placing limits on tour lengths in an unconventional war that never showed signs of ending, especially one that was quite unpopular among Americans, had both very real positive and very real negative consequences.
And there was another aspect that remains important although nebulous: The tour limits gave rise to "short-timer" calendars that ticked off the remaining days a man had to remain in country; the 180-day mid-point was the tipping point for Army soldiers, and a man's calendar gradually affected his thinking about what he was doing. If the war never ended, at least the "short-timer" calendar did - IF the soldier could remain alive long enough to check off that last day. And the closer he got to that last day, the more important it became to him that he stay alive by avoiding dangerous situations as much as possible. Individual survivability eventually competes with, and might even supersede, military mission - a tendency better balanced by rotating whole units despite the extra cost. The psychological effect of "short-timer" calendars in such a constant unconventional warfare environment gradually got blurred with "combat fatigue" and "burn-out", so that it was nearly impossible to distinguish one from the other or to sort out what was actually going on in a man's mind. Nor was the psychological aspect of the soldier viewed at that time worth even considering; at the end of the year, most surviving and mobile Army draftees were simply flown back to the US and mustered out of service, a jungle-to-street journey that rarely took longer than 24 hours. These were the human male widgets who somehow engendered the women's "liberation" movement in America.
With all of that having been said, it was still possible for Army and Marine career soldiers to serve two, three or four tours "in-country", each separated by a period of assignment outside Vietnam or back in CONUS (Continental US). And some of those tours could have been for periods longer than 12 months. Army personnel are authorized to wear on the right lower jacket sleeve one perpendicular golden hash mark for each six months served in a combat zone; it was not uncommon during the Vietnam era to see professional Special Forces men with as many as ten of these hash marks on their uniforms.
It should be noted that most practices with male soldiers in Vietnam, with the exception of tour length limits, pretty much mirrored practices throughout 200 years of American history before 1975. Following on centuries of practices of European monarchies, there had always been a certain "expendable" aspect to American soldiering. Today we fight wars more intelligently, with the knowledge that ground soldiers are actually valuable assets and that all other military assets exist to support their enormously complex and incredibly dangerous mission among other humans on the ground. Unfortunately, the US Military doesn't have half the number of ground soldiers to execute properly the various missions that today's politicians want it to execute, tour limits or not, but the politicians still prefer to pour taxpayer money into unnecessary military toys intended for conventional warfare that generate civilian jobs and votes back home, while hoping that American ground soldiers thrown into any situation will eventually figure out how to solve it. European politicians play the same game with American soldiers and taxpayers, placing far greater burdens on Americans than they are willing to deliver as equitable "allies".
Naval shore personnel generally served one year tours such as at NSA Danang. Navy Seabees served from six months to ten months or more with a Mobile Construction Battalion. If Seabees were assigned to a shore activity, generally they stayed a year. Brown water sailors usually served a year tour, but could be more or less. Seabees could extend with relieving battalion and stay anywhere from eight to twenty months depending on the battalions work schedule. I have heard of Seabees doing four tours with battalions, or a tour or two with a battalion and another with a shore station such as NSA Danang. Navy Corpsmen serving with Marines generally did thirteen month tours, same as Marines. Some Seabees served aboard ships in the Yellow Sea patrolling the coastline. These Bees served as long as the ship stayed on station.
Footnotes:
1. Vietnam was an unconventional war, fought in a set geographical space over a very long period. It began under President Eisenhower with the introduction of the 1st Special Forces Group in 1957 (900 in 1961), increased under President Kennedy (16,000 in 1963), and escalated dramatically under President Johnson (543,482 in 1969); official US military involvement in Vietnam ended 16 years later under President Nixon with the withdrawal of the last US military forces in 1973. Over those 16 years, a total of 2,644,000 American military members served in-country in Vietnam, about half of whom (1.3 million) were routinely exposed to combat and 80% of whom had at least a high school diploma. Only about 29% of those serving on US military active duty during the period actually saw service in Vietnam; 71% did not. Of the 1.73 million men drafted during the period (only 2.5% into the Marine Corps), just 38% actually served in Vietnam. About 25% of those serving in-country were ground forces draftees, and they accounted for 30.4% of combat deaths, but it's not known how many men volunteered to avoid being drafted. The war, which had an overall US casualty rate of about 13.7%, resulted in 58,202 Americans killed, 1,700 missing and 303,635 wounded. (South Vietnamese military losses were 3.8 times larger in all categories.)
2. The war was mostly static, rather than fluid (as was, say, the global WW II). Static unconventional wars that go on and on are very different from conventional wars that are continually driving to some clear conclusion as rapidly as possible. (The first three weeks of the Iraq War, for example, were entirely conventional fluid attack, and then immediately shifted to unconventional static occupation, but without adequate and appropriate US personnel and equipment for unconventional warfare / military occupation, including counter-insurgency, reconstruction, and stability operations.) The two types of war are almost exact opposites, requiring very different expertise, equipment and configuration; fluid conventional is all about offense, about destroying things and killing people, while static unconventional is all about defense, about building things and helping people. (Because of very significant ground forces personnel shortfalls, today's American super-soldiers are expected to shift from offense to defense and back to offense on a dime without missing a beat; most consider that expectation unrealistically naïve in an environment where a single mistake in a half second can result in death. Americans would never consider asking their professional football teams to do that in a completely safe and controlled environment.) Static unconventional wars place much more emphasis on defending stationary base camps and civilian populations, a "backward leaning" requirement that draws huge numbers of soldiers away from performing "forward leaning" aggressive attack against moving enemy targets. In Vietnam, American forces had to commit many more soldiers to static defense than it could commit to fluid offense. So it was highly likely that a combat soldier would be employed in both roles (offense and defense, within an unconventional environment) during his 12-month in-country tour, and very often one role was just as dangerous as the other.
With the possible exception of US Navy surface fleet officers, US Navy Swift Boat officers performed 1 year tours in South Vietnam. US Army officers conducted one year tours in RVN but generally only 6 months IN THE FIELD; then they were rotated to staff positions in the rear. But they still did 1 year in country.
The US Navy had two navies during the Vietnam War: the Brown Water Navy and the regular fleet. The Brown Water Navy was the "Riverine Forces", consisting of Swift Boats (PCF-Patrol Craft Fast), PBR's (Patrol Boat River), Alpha Boats (ASPB-Assault Support Patrol Boats), and Monitors (River Battleships). The US Navy Fleet warships consisted of Aircraft Carriers, one Battleship (USS New Jersey with 16" guns), Cruisers (6" guns for Light Cruisers, 8" guns for Heavy Cruisers) and Destroyers. Fleet warships "normally" conducted WESTPAC cruises (Western Pacific); for US Destroyers (5" guns) they worked the "Gun Line" off the coasts of North & South Vietnam. The Gun Line consisted of firing onto enemy targets along the coastline, often engaging Communist Shore Batteries. Normally WESTPAC cruises lasted about 6 months, thru rotations. US Warships working the Gun Line and supplying Air Strikes North of the DMZ were called YANKEE STATION. South of the DMZ was DIXIE STATION.
Other branches may have been different.
The US Army original tour was 12 months (drafted or volunteer/US or RA). Extensions in Vietnam were in 6 month increments after that original tour. Example: for a US Army serviceman; three tours would be only 2 years (12 months plus 6 months, plus 6 months again=24 months=2 yrs).
After your 12 month tour of duty, under normal circumstances, they couldn't make you stay any longer (other than admin errors, misc. etc.).
However, there once was a GI frantically digging a hole at a firebase one night. When approached and asked why he was so "desperately digging", he replied with some anger, "you've never been over-run...have you!? (as he continued digging) "...well I have! In this very @@#@# spot! I was with the Marines...we got over run...everybody was shootin everybody...couldn't tell who was who...I never want to go thru that ##@# again! So I couldn't get a job when I got out...needed a job...so I joined the Army; knowing the army wouldn't send me back to this place...and what happens?! They send me back to this very same spot that we got over-run when I was a marine!"
The moral of this incident, is this: sometimes a man volunteered for an extra tour of duty in Vietnam and didn't even know he did.
Combat tours in the Vietnam war may have varied in the different US branches (US Marines, US Sailors, US Airmen, US Coast Guardsmen). For US Soldiers the initial tour was 365 days (one year). Second and third tours were in 6 month increments. Another words a US Soldier who did 3 tours actually did 2 years.
Vietnam vets fought a different type of war , some classify it a a conflict similar to the Koren war . Nam vets were required to a year tour of duty , 13 months for the marines compared the duration of the war for older vets . The older vets also less of a profile at home because the the larger numbers involved . And were sucessful at the end .
For US Airmen, US Sailors, Marines, Coast Guardsmen, it may have been different. But for US Soldiers it was a one year tour of duty. Second and third tours were in six month increments. So, for a GI (US soldier) three tours meant 2 yrs.
When referring to the US casualties, some men were hit within 30 days of in country duty (after the 1 to 2 week RVN orientation-Republic Vietnam Orientation). Some GI's were hit with less than 30 days remaining of their tour. Those men were called "short timers", and as time passed, the Army often went out of their way to assign those GI's to rear area duties.
It was the first victory that the continental army had after a string of crushing defeat in Boston. the soldiers moral and inspired many to reenlist in the army for another tour of duty.
i did a report a long time ago in school and researched this information. On average there were only about 35,000 combat soldiers in Vietnam, on the average. Which made up only about 10% of the total American soldiers in Vietnam. It takes alot of support personnel to take care of the logistics, administrative needs, and etc... for each combat soldier. The number of combat soldiers in Vietnam rose to approximately 50,000 combat soldiers during the Tet Offensive.
7 months
A typical duty in the 1960s for the US Marines did last for several months.
one year
His tour of service from 1968 to 1970 only included the normal tour of duty in Vietnam of 12 months
ABC Scope - 1964 Vietnam Report Tour of Duty 2-33 was released on: USA: 16 April 1966
See: Statistics about the Vietnam War
During his tour of duty in Vietnam, Forrest was shot in the buttocks.
Oliver Stone
The show was Nam: Tour Of Duty.
The tour of duty for a US Marine in Vietnam was thirteen months although a Marine could extend his tour in Vietnam .
Forrest did a tour of duty in Vietnam. He described his experience there as taking long walks looking for a guy named Charlie. When their platoon was attacked, Forrest pulled five of his mates to safety and later received the Medal of Honor for his bravery.
There was China Beach about the Vietnam war that ran between 1988-1991. There was also "Tour of Duty" that ran 1987 - 1990, about at the "tours of duty" of several members of a platoon during the Vietnam War.