"Tour of Duty" ran for 58 episodes, spread out over three series and aired between 1987 and 1990.
The three series can be seen as distinct from each other as the core group of main characters change locations in between series, which is explained as them being "assigned to other duties", but in the real world, it was due to the producers wanting to cut down the cost of location filming.
Initially filmed at a marine base in Hawaii, series two saw the production move to Los Angeles, explained in show as the unit being "Reassigned to SOG duties" and being based in Saigon; this led to a running joke of the same locations being used multiple times, but always as "something different". The second series saw the introduction of numerous female characters in an attempt to entice viewership away from rival network ABCs "China Beach", which was also set during the Vietnam war but focused on the lives of a group of Army nurses, it didn't work.
The core characters of this series are introduced in the first episode, which starts the series off in early 1967:-
2nd Lt. Myron Goldman is the officer who is assigned to command Bravo Company, 2nd Platoon; following the death of their commanding officer in combat during the opening scenes of the pilot episode.
Staff Sergeant Zeke Anderson has been in effective command of the unit, and as a long time Vietnam veteran, he provides much needed advice to Goldman.
Both characters bond over the course of the series, with both men learning to respect each others abilities.
The remainder of the unit changes over the course of the fulls series, with troops either returning home at the end of their terms of service, being killed or being removed from the unit for various reasons (its usually a sign that when a new face appears in rank and file of the unit, it means that they will either be killed by the end of the episode, or discharged for some, usually dishonourable, reason). The unit itself is made up of a variety of "stock" characters, and over the course of the series the unit goes through various iterations of these characters, complete with their stereotypical back stories explaining their various outlooks on life and hangups etc, what is surprising though is that the series writers have no qualms about killing off established members of the unit.
The series writers also had no qualms about making whole episodes which had very little by way of machine gun exploding things action and instead concentrated on individual characters and stories looking at things like racial prejudice, drug abuse, sibling rivalry etc etc. This is one of the things which makes the series stand out amongst series of a similar premise, as not only was the war and its various foibles explored, but so was the everyday lives of the people fighting in it, and moreso, the consequences associated with their particular foibles.
By the time of the third series, which saw Carl Weathers in the role of Colonel Brewster take over and assign the platoon to undertake "secret" missions behind enemy lines; came around, viewing figures for the series had dropped significantly, which wasn't helped by CBS "schedule hopping" the show so that it eventually ended up directly competing with NBCs "The Golden Girls". The series was cancelled after the third season drew to a close.
One of the things about the series was its use of time accurate pop music, so much so that several compilation albums were released, however, in a legal oddity, when the series was released on DVD in the US, all of the series music was replaced, including the shows iconic use of "Paint it Black" by the Rolling Stones as its theme tune, by generic "soundalike" tunes or original instrumental compositions, this didn't go down too well, especially as fans of the show outside of the US got a completely unedited DVD release, including all the music and a lot of the violent bits that were cut out for US release.
While the series started out strong, the gradual erosion of its main concept and attempts to make the show more "family friendly" led to its eventual position of being yet another generic military program with talky bits.