CBS was sure this Christmas movie was going to crash and burn. They barely promoted it, the network expected terrible ratings, and even one of the animators worried they had “ruined Charlie Brown” for good. But on December 9, 1965, something completely unexpected happened. Nearly half of all TVs in America flicked over to watch it—millions of families gathered around, curious to see what this strange little holiday special was all about. And just like that, what CBS feared would be a total flop turned into a beloved holiday tradition that still warms hearts today. So what exactly freaked the network out so much?

“Television is running a big gamble,” wrote television reporter Val Adams in The New York Times on August 8, 1965. “It will attempt a half-hour animated cartoon in color based on the newspaper comic strip ‘Peanuts.’ In lifting ‘Peanuts’ characters from the printed page and infusing them with motion and audibility, television is tampering with the imaginations of millions of comic strip fans both well and self-conditioned on how Charlie Brown, Lucy and others should act and talk.”

Newspapers, though not The Times, of course, had delivered the tales of the “Peanuts” characters to American doorsteps every day since October 2, 1950. The group’s personal and social misfortunes captured American sentiment: for not much more than the cost of Lucy van Pelt’s 5-cent therapy booth, readers could relive their childhood angst through the antics and quips of Charlie Brown and his gang. And they would for another 50 years, for as creator Charles Schulz would later reflect, “All the loves in the strip are unrequited; all the baseball games are lost; all the test scores are D-minuses; the Great Pumpkin never comes; and the football is always pulled away.”

The public would have specific expectations, then, when CBS aired for the first time an animated adaptation of the comic strip on December 9, 1965. The greater gamble for the network, though, was how airing an animated children’s special at night would change its primetime philosophy.

As has been widely reported, “A Charlie Brown Christmas” incorporated unexpected elements in its animation – the voices of children instead of trained adults, jazz music, a Bible passage, no laugh track. But the team behind the special had toyed with the screen presentation of the characters years before, first in a 1959 Ford Motor commercial. Schulz, fiercely protective of his creation, only allowed the “Peanuts” crew to participate after seeing the work of former Disney animator Bill Melendez, who preserved Schulz’s seemingly inimitable style.

A few years later, Melendez reunited with the characters when Schulz agreed to collaborate on a documentary with Lee Mendelson, a television producer. Mendelson wanted a few minutes of animation for the project – about Schulz and his history with “Peanuts”—before  marketing it. He couldn’t sell the program, but at least one advertising firm on Madison Avenue remembered the project when Charlie Brown and company landed on the April 9, 1965 cover of Time magazine: McCann-Erickson, the agency representing another of America’s most beloved institutions, Coca-Cola.

The Coke and Pepsi advertising wars of the 1960s took to the television airwaves as the central battlefield. “The Pepsi generation” came into vogue in 1963, and in 1964, Pepsi Co. doubled its volume of advertisements, increased its television budget by 30 percent, and tripled its market research budget. That same year, it teamed with Disney to present “It’s a Small World” in the Pepsi pavilion at the World’s Fair in New York.

As the next parry in the advertising wars, Coca-Cola, McCann-Erickson executive John Allen told Mendelson, wanted to sponsor a family-friendly Christmas special in 1965. Could he produce a Charlie Brown one? Mendelson said yes without asking Schulz, but the cartoonist agreed to give it a go. The two sent off a one- page triple-spaced treatment a few days later. Coca-Cola accepted it right away.

CBS executives outright rejected the Charlie Brown Christmas special when McCann-Erickson first pitched them. It wasn’t that they didn’t think animated shows could succeed in prime time: NBC had aired the Christmas special “Rudolph the Red-Nosed Reindeer” at the end of 1964, and for several years already, ABC had a hit with Hanna-Barbara’s “The Flinstones,” television’s first half-hour animated sitcom. In the 1950s, CBS had experimented with animated shorts in its nighttime line-up, but these disappeared in 1959 when James Aubrey became president of the network. He didn’t believe in specials, seeing them as programming interruptions that distracted “habit viewers” from their routines. Children fell into this category for Aubrey, and as they expected cartoons on Saturday morning, not on a weeknight.

Although a volatile presence, Aubrey was a good steward of the CBS reputation. The “Tiffany network,” named such for its high-quality programming, had established itself with outstanding broadcast journalism, lead by Edward R. Murrow, during the post-war television boom. For the next 20 years, the network struggled with the balance between journalism and entertainment. Several years before the Charlie Brown Christmas special, Murrow had left CBS after a long series of publicized arguments with Aubrey’s boss, CBS corporation president Frank Stanton. Murrow’s main concern was “television’s inadequate coverage of grave world problems.” Stanton, in a speech to CBS network affiliates on May 4, 1962, said, “CBS cannot agree that we ought to conceal the fact that we are diverted by mystery dramas or westerns or situation comedies.”

Under Aubrey’s leadership, these mystery dramas, westerns, and situation comedies appeared at the same time on the same nights every week for the benefit of “the habit viewer,” placing CBS at the top of the ratings. In a May 1976 article, New York Times reporter Les Brown noted that only when Stanton fired James Aubrey in early 1965 did CBS culture begin to entertain specials (then called “spectaculars”) other than documentaries; even then, the television events aired infrequently, in conjunction with “a big-name personality or the presentation of a play or news documentary.”

Charles Schulz and “Peanuts” fit that description. But airing “A Charlie Brown Christmas” was indeed a gamble. Both Charles Schulz and his “Peanuts” gang had big-name personalities, but not the kind that fronted variety shows. With Aubrey ousted in February 1965, and the “Peanuts” proposal before them just two months later, CBS had little time to experiment with specials, and no experience with half-hour prime time animation. According to The Times, CBS executives agreed to A Charlie Brown Christmas once they realized that Stanton was a friend to Schulz and a fan of the comic. Meanwhile, Schulz, Mendelson and animator/director Melendez only had six months to put together a half-hour animated special. None of them had attempted the feat before.

Quickly, the proposal’s bare bones came together: the ice skating, the skinny little tree, the debate over Linus’s Scripture reading (Mendelson and Melendez balked, Schulz insisted), the hapless dialogue that fans had come to love from the lips of little Charlie Brown (“I know nobody likes me. Why do we have to have a holiday season to emphasize it?”).

Three weeks before screening the special for CBS, Mendelson and Melendez watched it in a small room full of animators. The pace felt slow. The music didn’t quite fit every scene. The kids’ dialogue sounded stilted.  In Charles Solomon’s The Art and Making of Peanuts Animation: Celebrating 50 Years of Television Specials,, Mendelson remembers Melendez turning to him and saying, “I think we’ve ruined Charlie Brown.”

So thought Neil Reagan, an executive at McCann-Erickson. “This isn’t very good,” he said when he checked in on the work for his client.

Some of these early concerns could be improved upon. Realizing that the Vince Guaraldi instrumental for the opening ice-skating sequence needed lyrics, Mendelson jotted down the poem “Christmastime is Here.” The actors’ cadences were harder to edit. For the short documentary “The Making of a Charlie Brown Christmas,” Mendelson indicated that is why music accompanies some of the dialogue.

Days before the air date, CBS—which had taken the gamble of this drastic sidestep from their successful primetime philosophy—had the opportunity to take their first look at the special. Fred Silverman, a former CBS programming executive, was in his late 20s during the time of the viewing.

“The general reaction was one of some disappointment,” he remembered. “That it didn’t really translate as well as we thought.”

“[CBS executives] didn’t get the voices,” Mendelson told The Washington Post. “They didn’t get the music. They didn’t get the pacing.” CBS would only air the show, executives said, because they had already scheduled it to run the following week.

Prior to the airing, Time magazine published a review of the special that presaged its overwhelming reception. “A ‘Charlie Brown Christmas’ is one children’s special that bears repeating,” wrote Richard Burgheim.

On Thursday, December 9, 1965, over 15 million households tuned in to judge for themselves.  The reception would turn the special into a classic. CBS soon learned that nearly half of American television sets had watched what the network thought would be a flop.

“What did I know compared to Charles Schulz?” remembered former executive Fred Silverman. He had been concerned about how the comic would translate onscreen, and although the show was a hit, some critics agreed that the transition was disappointing.

“It was not a bad show, but many of the strip’s purist fans probably experienced a letdown,” wrote Walt Dutton in the Los Angeles Times the next day.

CBS called Mendelson and ordered four more specials.  Less than one week later, CBS announced that it would rebroadcast the special the following Christmas,.  It didn’t change a thing, other than removing Coca-Cola branding from the opening and closing sequences (The following summer, Coke sponsored another “Peanuts” special, focusing on Charlie Brown’s ill-fated baseball career, but its sponsorship ended before the Christmas special ran again in 1966. Gradually, the advertising market shifted to the more profitable scheme today of multiple sponsors per show.)

Mendelson. Schulz and Bill Melendez were shocked at the program’s reception.

“I thought ‘good Golly,’ I’m suddenly involved in something that’s big,” said Bill Melendez.

“We only expected it to be on once, and then never heard from again,” Lee Mendelson told Coca-Cola’s website in a recent interview.

In 1966,  “A Charlie Brown Christmas” would go on to win a Peabody and an Emmy for outstanding children’s programming,  The success of “A Charlie Brown Christmas” changed the network’s prime-time philosophy. The following year, CBS telecast a second prime-time animated holiday special: the adaptation of Dr. Seuss’s “How The Grinch Stole Christmas.” And in 1969, it aired “Frosty the Snowman.”

By the mid-70s, CBS aired about 80-90 television specials annually (as did NBC and ABC), including sports events, pageants, awards shows, variety programs, and made-for-TV movies. In 1971, program executive Fred Silverman spun the success of one such film – called “The Homecoming” – into a series that his colleagues didn’t think would last: The Waltons, which ended up running from 1972 until 1981.

“A Charlie Brown Christmas” ran annually for 35 years on CBS, until ABC acquired the rights in 2001, a year after Charles Schulz died. The show was the first of more than 45 animated Charlie Brown television specials.

“The continued success of the special has surprised me as much as anyone,” Charles Schulz said to TV Guide in 1985. “A lot of the drawings are terrible.”