It’s not often that a seven-year-old on Martha’s Vineyard can change the lives of servicemen and women halfway around the world, but that was the case when Jack Nixon came up with the idea to bring veterans to Martha’s Vineyard to participate in the Striped Bass and Bluefish Derby almost a decade ago.

On Menemsha Beach Thursday night, Island residents witnessed the realization of Jack’s dream through a screening of Bob and Sarah Nixon’s film, American Heroes Saltwater Challenge. The 2013 National Geographic documentary follows a half-dozen wounded warriors who participated in the derby as part of the Nixon family’s Saltwater Challenge. Although Jack is now almost in college, the challenge lives on — both onscreen and off.

“We didn’t plan to make a film for this,” Mr. Nixon said. He initially pitched Howard Owens, the president of National Geographic, about doing a film on science, fishing and conservation. “He was like, no, I’m not interested. But I’ll tell you what, I want to do a movie on that thing you guys do. The thing I read about in the paper with the veterans.”

The derby was only a week away, but Mr. Owens wasn’t worried. “He was like, yeah...go do it,” Mr. Nixon recalled.

Sarah and Bob Nixon started the annual fishing experience at the request of their son Jack. They also created the documentary for National Geographic. — Albert O. Fischer

It took a lot of work to make the production happen. Sarah Nixon, an indefatigable force when in pursuit of a goal, tracked down musician John Mayer at a concert in North Carolina and convinced him to create original music for the movie. It was the first documentary Mr. Mayer had ever scored.

She then pestered Green Beret Ben Harrow, one of the film’s stars, for so long that he filed a complaint with the Army.

“But it worked! I followed him in my minivan all the way to his apartment and his wife was like, who is this chick?,” Ms. Nixon said.

Even though the film premiered a few years ago, many Vineyard residents missed the opening because it aired on the National Geographic channel. When the folks at National Geographic heard it was going to be shown on the Menemsha Beach, they were so excited that they remastered its surround-sound audio for the occasion.

Buddy Vanderhoop and Jennifer Clarke, two fishing captains featured in the film, were in attendance.

Jeremy Mayhew screened part of his new film at the event. — Albert O. Fischer

“It was such a pleasure to have those guys on the boat,” Mr. Vanderhoop said. “They’re such young kids who have given life and limb for our freedom. What more could you ask of a soul?”

The crowd at Menemsha Beach was all smiles as it watched its local heroes guide its national ones. Along with Mr. Vanderhoop and Ms. Clarke, the film included charter captains Lev Wlodyka, Scott McDowell and Jonathan Boyd. When the five fishermen, wearing galoshes and overalls, walked across the gritty onscreen seascape in classic National Geographic fashion with the narration of Lenny Clarke in the background, the viewing audience burst into both laughter and applause.

But that laughter quickly subsided as the veterans, many of whom had lost limbs to IED’s, told their remarkable stories.

Ms. Clarke became emotional when talking about her experience with Sgt. Monty Bernardo who lost both his legs and his right hand in Afghanistan.

“Monty was incredible,” she said, choking back tears, “so incredible that Sarah brought him back another two years to fish because we got so close.”

By the end of the movie, Sergeant Bernardo was no longer fishing in his wheelchair. He’d situated himself on the side of the boat like a seasoned professional.

“It just goes to show you that it just takes one little idea to make a change in many people’s lives,” Mrs. Nixon said.

Mr. Vanderhoop, who admitted to being initially reluctant to participate, seconded that statement. “Yeah, Sarah twisted my arm. It still hurts,” he said. “But if I had more money and more time, I’d do it for a whole summer for those guys. It was such an honor.”