The third season of 12 O'Clock High was really a half-season, and is the least well-remembered of the three years it was on the air. It was also the only season in color, which created endless problems, in terms of budget and airborne footage, and probably sealed the doom of the program as much as the changing times and shifting tastes of the public. Television had been making the transition to color very gradually since the start of the 1960's, spearheaded by NBC which, as an offshoot of RCA Victor -- which held the patent on the US color television system -- had a strong interest in selling the sets (what we now call the hardware). CBS made the jump to color broadcasts in 1966, and ABC, then the poorest of the three networks, was forced to follow suit -- but the question arose of who would actually pay for color shooting. (That matter killed The Patty Duke Show, which would have been brought back for a fourth season but only if United Artists, the company producing it, paid for color filming).
12 O'Clock High came back for a third season in color, but that decision created all manner of problems. For starters, it rendered useless any stock footage from prior seasons; and it severely limited the amount of actual World War II footage that could be used. Additionally, the more expensive shooting required that a major change took place in the action, which affected the scripts -- in order to save money, the character of Colonel Joseph Gallagher (Paul Burke) was usually depicted that season as flying in a pathfinder capacity, in a single-engine fighter, rather than in a bomber with a full crew, in order to save money (in terms of other actors in the shot etc.) on his airborne scenes. Even more damaging to the series' prospects for survival was the calendar -- by late 1966, the United States was involved in a new war, in Vietnam, which had far less popular support than the Second World War ever did. Less and less of the public was interested in tuning in every week to stories that seemed ever more out of a receding past; and there weren't yet quite enough color television receivers in use for those viewers to have made a difference (at least not to ABC -- NBC renewed Star Trek at least once because of the network's connection to RCA Victor and the color television patent). The series was cancelled midway through the season, which only produced 17 episodes. These have been seen in syndication and on cable far less frequently than the two black-and-white seasons. ~ Bruce Eder, Rovi