Filmmaker Melinda Hess was going through boxes of family artifacts that had been collecting dust for a quarter-century when she discovered a series of letters that revealed disturbing secrets about her father’s work in the 1940s.

Nestled among grade-school report cards, a bar mitzvah photo and a marriage certificate was a brown leather suitcase containing a series of numbered letters in Army-issued envelopes.

All but one of the letters were sent from Fort Bliss, Texas, where her father, an Army private, was part of a secret project working on rockets — with a team of scientists and engineers who had come from Nazi Germany.

How, Hess wondered, could her father, a Jew from New York, have collaborated with former Nazis such as Wernher von Braun, a leader in the design and development of the V-2 rockets that Germany used in 1944 to bomb England, France and Belgium? How could her dad have socialized with men who used concentration camp inmates as slave laborers in the development of those rockets?

“To read that your father is speaking very well of former Nazis was really shocking,” she said. “I was kind of horrified. It took me some time, it took a lot of thinking, a lot of reading, to come to almost a kind of forgiveness to my father for writing these things.”

Those feelings, and the questions Hess had that could never be answered, turned into the basis for a film she is writing about her dad and his letters. Hess hopes to complete the film, “Letter from Cloudcroft,” by the fall of 2019.

Hess will be speaking about her plans for the film, and trying to raise money to support the project, on Jan. 11 at the Jewish Community Library in San Francisco. Hess lives in San Francisco, where she just completed a two-year filmmaker residency stint at the Jewish Film Institute, as well as in New Mexico.

Sandy Hess, her father, was 21 and a mechanical engineering graduate of New York’s City College when he moved to Texas as part of the rocket-design program. There he met and befriended some of the hundreds of German scientists, technicians and engineers brought to the U.S. after World War II by American officials competing with the Soviet Union for their expertise.

The Germans, many of whom had been Nazis, were brought to the U.S. as part of the secret Operation Paperclip. Some of them, such as von Braun, went on to become key figures in the U.S. space program.

Sandy Hess’ letters, all sent to his parents back in New York in 1946, talk about his work in Texas and his life there, from the meals he ate to the scientists he hung out with in the German beer garden. Each of the letters was numbered.

When Melinda Hess found the letters, she discovered that number 31 had never been opened. It was from the Lodge Resort in Cloudcroft, New Mexico, where the Fort Bliss scientists and engineers sometimes went for weekend getaways. Since her dad died in 1989 and her mom and grandparents also had passed away by then, she had no one to ask why the letter was still sealed.

When she went to open letter No. 31, her filmmaking and life partner Patricia Antelles grabbed it from her and insisted it be opened on camera, which Hess later did surrounded by family and friends.

“I asked Patricia to hand me the letter opener,” Hess said. “Instead of handing it to me, she flung herself across the room and said you’re not opening this now, one day you’ll open it on camera. She recognized the potential for its media possibilities.”

The film will examine the letters, and the rocket-design project, from two perspectives — that of Sandy Hess in 1946 through his writings, and of Melinda Hess today. For her, it’s a personal exploration of her relationship with her father and of trying to understand his thoughts at the time.

He never discussed that period of his life with his daughter. Melinda doesn’t know if her mother, who met Sandy about five years after his time at Fort Bliss and Cloudcroft, knew anything about her husband’s work there.

Research into the film has helped Hess answer some questions about that period in her father’s life, though others remain unsolved. The letters show that Sandy Hess also had questions about his German coworkers that he could not answer.

“My father, he asks his parents a couple of times, ‘I wonder if they know I’m Jewish, they’re certainly treating me wonderfully and I wonder if they would if they knew I was Jewish,’” she said.

Filmmaker Melinda Hess will talk about her film-in-progress, “Letter from Cloudcroft,” at 7 p.m. Thursday, Jan. 11 at the Jewish Community Library, 1835 Ellis St., S.F.