A black locomotive chugs past mourners lined eight deep to catch a glimpse of the flag-draped coffin being carried from New York to Washington, D.C. A narrator’s sober voice speaks over mournful instrumental music that sets the tone for a tribute film to fallen Sen. Robert F. Kennedy (D-N.Y.).

“In the life of this exciting man there had been some splendid excitements, and now it would return only in the memory,” the narrator says as the train glides along. Photos of a smiling Bobby Kennedy,

assassinated on June 5, 1968, appear on the screen.

This is the opening scene of Charles Guggenheim’s “Robert Kennedy Remembered,” the tribute film that first aired at the 1968 Democratic National Convention in Chicago a few months after Kennedy’s assassination. The film won an Academy Award.

The film has been shown only a handful of times since 1968, when it brought action on the convention floor to a halt and supporters to tears. And now there’s another opportunity to take stock of Robert Kennedy’s life: The documentary will be shown at 7 tonight at the National Archives, followed by a panel discussion to recall the late director’s work.

Guggenheim’s black-and-white film was shown at film festivals at both the Democratic and Republican conventions this year, the 40th anniversary of Kennedy’s death. Today hailed as a chronicle of history, the film was originally an emotional tribute that hushed rioters and fractured Democratic convention-goers for 28 minutes.

“It brought the convention floor down to a standstill,” said Grace Guggenheim, the director’s daughter, who was just 10 years old in 1968. “It allowed people to remember this momentous event. It was so complicated. It was so tragic.”

The 1968 film opens grimly, but it takes the viewer through an emotional experience that reflects much of the optimism that Kennedy’s presidential campaign evoked. Like Guggenheim’s other film on Kennedy, which focused on his 1964 Senate campaign, it shows the candidate speaking before massive crowds and comforting impoverished children.

“Toward the dispossessed and the powerless, he had a deep concern,” the narrator says as Kennedy reaches out for the hand of a hungry and tattered youngster.

Guggenheim specialized in political biographies, producing films for Adlai Stevenson and George McGovern’s presidential campaigns. His daughter Grace now presides over Guggenheim Productions in Georgetown. Charles Guggenheim’s son Davis, carrying on the family tradition, is a filmmaker in Los Angeles and produced the biographical film of presidential nominee Sen. Barack Obama (D-Ill.) screened at this year’s Democratic convention.

“It’s very fitting to screen this film this year,” Grace Guggenheim said of her father’s work, noting this year’s historic presidential race. “This was the year to do it.”

Before his death in 2002, Charles Guggenheim was a board member at the National Archives. Guggenheim donated one of his Oscar statues to the museum, and in a tribute to the filmmaker, the Archives launched the Charles Guggenheim Center for the Documentary Film in 2004. The center hosts educational programs and symposiums, and screens Oscar-nominated documentaries and short films every year. (For those who miss tonight’s screening, the DVD is for sale through the Robert F. Kennedy Memorial.)

The 1964 biographical film, which at 28 minutes is much longer than the abbreviated clips shown by candidates today, follows Kennedy’s rise from law school to attorney general, and from sporty younger brother to the bearer of the Kennedy torch.

Taking viewers from Poughkeepsie, N.Y., to Watertown, N.Y., as Kennedy campaigns for Senate, the 1964 film was meant to energize New York voters and offer a behind-the-scenes look at the younger Kennedy brother.

“Kennedy was controversial. He had a ruthless reputation,” Grace Guggenheim recalled. “My dad changed that. If you look at the [1964] film, he’s shown as a family man.”

Kennedy wrestles with his nine children and notes that marrying his wife, Ethel, was “the most important decision in my life” in the charming film. But Guggenheim also follows a less cheerful Bobby Kennedy in the wake of his brother’s assassination. The younger Kennedy’s eulogy speech for President John F. Kennedy at the 1964 Democratic convention, in which RFK eloquently quotes Shakespeare’s Romeo and Juliet, is both a touching and proud moment that almost foreshadows Guggenheim’s later tribute to RFK that would come only four years later.

The 1968 eulogy film includes scenes from Guggenheim’s earlier biographical piece, including shots of Kennedy climbing mountains and paddling through rough waters, playing football with his three brothers, and later, with his nine children. In many ways, the eulogy film strikes the same optimistic tone as the 1964 biographical film.

But unlike the 1964 film, “Robert Kennedy Remembered” ends with a lone Kennedy, rather than a surrounded one, walking along a misty beach and into the distance. Rather than Bobby, youngest brother Ted is the one making the eulogy speech, eloquently quoting a poet as his voice quivers.

“As he said many times, in many parts of this nation, to those he touched and who sought to touch him: ‘Some men see things as they are and say why. I dream things that never were and say why not.’”