The private ceremony inside the agency’s main lobby last year marked the first time the CIA publicly acknowledged Robbins as one of their own. But the slain secretary holds enough historic titles to make her an object of curiosity within the CIA. Robbins was the first woman at the male-dominated CIA killed in the line of duty. She is the youngest CIA employee ever killed. And, according to Panetta, she was also the first American woman to die in the Vietnam War.

The bombing and her death generated front-page headlines in U.S. newspapers. Yet Robbins remains one of the CIA’s more phantom-like figures, her mystery fueled by the agency’s decades-long refusal to publicly recognize her employment, despite her family’s pleadings and books that briefly described her CIA stint. Warren Robbins, her brother and only immediate family member still alive, was elated when the CIA finally inscribed his sister’s name in the Book of Honor.

It is Warren who inherited from his dead parents the one thing that most illuminates his sister’s time in Vietnam: a trove of 30 letters she wrote home, dating from her arrival in Saigon to the week before her death.

The letters offer a glimpse into the life of a young woman supposedly working for the State Department as she launched her career and looked for love amid Vietnam’s escalating violence.

“Reading these letters,” said Warren, 65, a retired airline mechanic, who hadn’t looked at them since he was a kid, “it’s like I got to know her all over again.”

August 6 1964: Dear Mother, Dad & Warren , “I think I’m going to really enjoy working for the State Dept. Security-wise we do have to be careful — but you’d never feel that way right here in Saigon if it weren’t for the Vietnamese Police all over the city.

Before her arrival in Vietnam, Robbins had never been out of the country. She had been born in South Dakota, spent her early childhood in Iowa and California and grew up mostly in Colorado, where her father, Buford, was a butcher and Navy veteran, and her mother, Ruth, was a homemaker.

In high school, she belonged to the bowling club. On Sundays, she attended a Lutheran church all day.

In 1961, Robbins headed off to a secretary’s school at Colorado State University and, after two years, somehow got recruited by the CIA. She wanted to combat the rise of communism. When she went to Washington in 1963, Warren said the family knew she was working for the agency. But they thought her Vietnam posting was with the State Department.

Three weeks into her assignment in Saigon, Robbins made it clear to her parents that they shouldn’t fret about the headlines back home.

August 25 1964: You probably know . . . that students were demonstrating and a bomb went off in the Caravelle Hotel. We in the Embassy were in no danger whatsoever. In fact, I walked both to and from work at lunchtime and you couldn’t tell anything different. I know you’re probably worried, but please don’t be.

The CIA’s Saigon station, headquartered at the U.S. Embassy, was the agency’s largest, boasting 400 employees throughout the country, according to “Sub Rosa,” a 1978 memoir by the agency’s station chief, Peer deSilva, who has since died. At the five-story embassy, which sat at a busy intersection near the Saigon River, Robbins managed employees’ time cards and typed up intelligence reports from officers, some of whom, deSilva wrote, were organizing rural villagers into little armies to spy on the Viet Cong.

October 7 1964: I don’t know where the last 2 months have gone. It’s so easy to forget even what day it is. I really do like my job. I have quite a variety of things to do & much of it is very interesting.

Her social life was ambitious, too. She told her family that she’d joined the Cercle Sportif, a social club that boasted a courtyard pool and tennis courts, and a membership of high-ranking diplomats and CIA officials.

Shortly before Thanksgiving in 1964, she and another CIA friend traveled to the coastal city of Nha Trang, a base for several CIA officers, and she wound up meeting an Army soldier named Bill McDonald. The two rented a fishing boat, lay down on their stomachs and posed for a photograph.

In the photo, McDonald is smiling, his legs bent upward, childlike. Up until he died in 2010 at the age of 66, he never relinquished those moments of romance, said Karen McDonald, his third wife, now an assistant U.S. attorney in Arizona. He’d posted the photo on an online memorial site for Robbins.

“After all these years, I continue to remember so much of the time Barbara and I spent together. . . . She is often in my dreams,” McDonald wrote in a 2010 e-mail found in his inbox by his widow.

But it would be another man, a 21-year-old Texan in the Air Force named Doug Johnson, who would become most important to Robbins.

Feb. 23, 1965: I like him maybe just a little bit more than most of the guys I’ve been going out with here . . . He likes to bowl, swim and even plays on a baseball (or softball) team at the base.

Soon, they were seeing each other every night. He had about a year left in Vietnam, and he was, she wrote, impulsive.

March 16, 1965: I certainly wasn’t prepared when I went out with Doug Sunday night and he asked me to marry him. It wasn’t as if the thought hadn’t crossed my mind, but hardly had I expected it then.

Johnson, who could not be located for an interview, and Robbins hashed out the marriage proposal for days. She worried that what they felt in Saigon wouldn’t be the same back home. But he loved her, Robbins explained to her family.

For me, I want no such thing as even as a trial engagement. When I say “yes” I’m going to mean it forever from that point on. This is probably one of the few times I’ve ever told you much about anyone I’ve gone out with . . . I hope this letter lets you see that your daughter, even though she may be half-way around the world, hasn’t let it all go to her head and still knows what’s good and right in this world.

It was late morning on March 30, 1965, and the CIA secretaries inside the U.S. embassy heard loud pop-pop sounds outside. Rosemary Dunn, Evelyn Flagg, Dorothy Peters and Robbins ran to the deputy chief of station’s office to peer out the windows.

A Citroen was parked outside, its hood up, while its Vietnamese driver was arguing with a policeman. The driver was being ordered to leave, and when he refused, the cop opened fire. Just then, another Vietnamese riding a scooter motored up alongside the driver and began shooting at the police officer.

That’s when Dunn noticed the smoke curling up from the Citroen, packed with 300 pounds of plastic explosives.

“I put my arm over my eyes, but the three others didn’t. We all four were lined up like ducks,” recalled Dunn, who lives in Sarasota, Fla.

Peters, 78, who lives in Leesburg, remembers running into the office: “Is that fireworks?” She turned to her right and, mere seconds before the explosion, looked at Robbins, who was wearing a light green skirt and yellow blouse.

“All I remember is that Barbara was holding a pencil. I turned to look at her, and that’s why I have scars on my face,” Peters said, noting that glass shards hit her left cheek, leaving permanent scars.

The enormous thud propelled everyone backward. The iron grates and windows shot out into the office like knives. The boxy air-conditioning units blew into the offices like little bombs. No one could hear Robbins. The only thing they heard was Dunn reciting the Hail Mary.

In his memoir, deSilva said he remembered walking out of the embassy past stretchers carrying women. He wrote: “I later found that one of them was one of my secretaries, Barbara Robbins, who was dead.”

* * *

The car bomb killed Robbins, another American and several Vietnamese, and injured at least 100 more. The secretary’s name and photo were splashed across the country’s newspapers: the Washington Daily News, Stars and Stripes, the New York Daily News — all describing her as a State Department employee.

Her body was flown back to Denver, and a funeral was held April 3, 1965. President Lyndon B. Johnson and Secretary of State Dean Rusk each sent sympathy telegrams to the Robbins family.

That year, the State Department held a ceremony honoring Robbins, placing her name on a plaque in its main lobby.

Warren suspects that his parents learned she was in the CIA in Vietnam shortly after she was killed. He said his father eventually told him in the late 1960s.

“I regret not being more inquisitive after she died,” Warren said.

In 1974, unknown to the family, the agency created its Wall of Honor and engraved 31 stars for fallen employees, including one for Robbins. She was the first woman to earn a star on the wall. But it wasn’t until 1987 that the agency held its first annual memorial ceremony for those recognized on its Wall of Honor.

By the early 1990s, the CIA began formally inviting non-agency family members to the ceremony, which up until then had been largely an employee-only event. In 1995, when the Robbins family attended its first Wall of Honor memorial service, the CIA for the first time read aloud all the names affiliated with stars during the ceremony, even if those names were not yet in the Book of Honor. On its Web site, the agency says those remembered with stars include a mix of covert officers, analysts, and support and technical personnel, as well as contractors.

Around the time of the 1995 ceremony, Barbara’s parents asked the CIA why their daughter’s name was not inscribed in the Book of Honor.

In a letter that Warren saved, a CIA official wrote to them: “I did check the records and found that your daughter’s name is not printed in our book of honor due to cover considerations.”

Some fallen officers have stars on the wall but no book inscriptions because the revelations might expose the agency’s sources and other methods.

In a statement, Todd Ebitz, a CIA spokesman, said the agency doesn’t discuss “the specifics of internal procedures” and would not disclose the reasons for the lag time between Robbins’s death and her placement in the Book of Honor last year. The agency, he said, periodically reviews the secret names of those with stars to determine when or whether those names should be revealed. The CIA, he added, has recently increased the frequency of its review process for those eligible to be honored.

In his 2001 book, “The Book of Honor,” former Washington Post reporter Ted Gup interviewed Robbins’s parents about their longing for the book inscription. “It sounded like they were trying to protect someone or something,” Ruth Robbins told Gup. “If they have a good reason, I guess we will never find out.”

Robbins’s father died in 1998 of cancer, and her mother passed away in 2008.

“Was she really just a secretary? That always bothered my parents. I’ve thought about this for years,” Warren said. “What was she there for?”

Finally, in May 2011, shortly before its annual Wall of Honor ceremony, Warren got a call from the agency. His sister’s name was being put in the book, an official told him.

“I was very taken away,” Warren recalled. “Like, ‘Wow. Finally.’ ”

The news also generated buzz at the agency. “People at the CIA were really excited that Barbara was publicly recognized for her service,” Ebitz said.

At the May 23 ceremony, Warren was given a front-row seat.

“When Barbara’s father asked his 21-year-old daughter, ‘Why Vietnam?’ the answer was clear and simple,” Panetta said. “She wanted to make a difference.”

After Panetta spoke, Warren shook his hand and congratulated the CIA chief on his new job as secretary of defense. They posed for a photo.

Now Warren just wants to know a bit more about what his sister actually did in Vietnam. And he wonders about the fate of Doug Johnson, whom Robbins wrote about in her very last letter home. Is he still alive?

March 23 1965: I imagine you’re still wondering about Doug. I still haven’t given him an answer and I may not between now and at the time he leaves. . . . The trouble is I’m not at all sure how I feel about him. Time, I guess, will be the deciding factor. That’s all for now. Love, Barbara