I found this while meandering around the web over the weekend: the TV GUIDE magazine advert promoting the two-hour series finale of New World Television's really rather excellent TOUR OF DUTY.
Despite what the copy suggests, this actually closed-out the series and not just the season. I was always under the impression that, by the time CBS aired this, they'd already decided to cancel the show but the wording suggests that the final decision still hadn't been made and renewal was still possible.
It was only a two-hour "special presentation" because CBS glued together the last two one-hour episodes (The Raid and Payback) and played them as a tele-movie. They certainly weren't scripted or shot as a two-hour piece.
It's also interesting that CBS Marketing opted not to include any of the show's regular cast. Lee Majors and Carl Weathers had been recurring guest stars in several third season shows. Pictured is Kyle Chandler who appeared in the last two episodes as a soldier who's blinded in combat (The Raid) and shipped back home (Payback) to cope with his injuries. Given the prominence of his storyline, it's safe to say that the producers were toying with making his character a regular had the shown been renewed.
The final episode marked a significant reboot in the format, again suggesting a very different Year Four had it happened. Several of the regular characters ended their tours and shipped back to the United States to start a civilian life. Had the show continued, story lines would have - presumably - been split between their attempts at readjusting to civilian life in a hostile world and the remainder of Bravo Company still serving in Vietnam.
Unfortunately, it was not to be.