By Jane Carr, CNN

(CNN) -- Do you like crossword puzzles and are you engaged to be married?

Those were the questions asked of many college-age American women by their professors, college presidents, or military officers to assess their suitability to do secret work breaking German and Japanese codes during the Second World War.

From students at the Seven Sisters colleges in the Northeast to schoolteachers from across the South, some 10,000 women answered the call and became the backbone of America's intelligence infrastructure. Their efforts saved lives and shortened the war. Code breaking was pivotal to the Allied defeat of Japan at sea and on the Pacific Islands, as well as to neutralizing the threat posed in the Atlantic by Nazi submarines.

Unlike the fits of genius dramatized in the films "Enigma" or "The Imitation Game," code breaking was actually a marathon of tedium, an activity defined by comparing and recognizing patterns. In this, women's abilities were thought to be superior to men's. Though they went about recruiting women quite differently, both the Army and the Navy saw in American women an untapped resource for improving America's odds for winning the war.

In her new book "Code Girls: The Untold Story of the American Women Code Breakers of World War II," journalist Liza Mundy tells the stories of many of these women who, because they were sworn to secrecy about the nature of their work, have been all but forgotten. Just because these women agreed to be invisible to the enemy, however, doesn't mean they need to be invisible to history.

Some of these barrier-breaking code breakers are still alive and in Mundy's estimation would be "delighted" by developments like the renaming of a residential college at Yale for Grace Hopper, "the queen of code" and "mother of computing" who was a pioneering American computer scientist and United States Navy rear admiral.

Says Mundy: "We need a few more buildings to be renamed or named after some of these figures and I hope that happens. I think it will."

On the occasion of the publication of "Code Girls," and International Day of the Girl on Wednesday, CNN Opinion spoke with Mundy about her experience writing a book about the women she calls "the hidden figures of the greatest generation."

This interview has been edited and condensed for clarity and flow.

CNN: Can you describe how you came to this project?

Liza Mundy: In a way, it's thanks to Sen. Daniel Patrick Moynihan. He insisted that the government consider declassifying its records around the Russian code-breaking project Venona, which started during the war and then continued for many decades during the Cold War. And because he prevailed, there was a document that was declassified, in which a wonderful NSA historian named Lou Benson wrote about the recruitment of a number of schoolteachers to work on it. Almost alone among historians, Lou not only noticed that there were a lot of women working on the Venona project, but he also thought that it was worthwhile to interview them. So while it was still possible, he interviewed a number of schoolteachers who were recruited during the war. And in many cases these women continued working on it for decades for the NSA. And I thought, "Well that's an interesting kind of small story for an article of a short book."

So I went out to the Cryptology Museum at Fort Meade [Maryland], which is attached to NSA. It's our own little version of Bletchley Park [the central site for British code breakers during World War II]. There were three wonderful women working there -- an NSA historian named Betsy Smoot, the curator of the museum, Jennifer Wilcox, and the incredible librarian there, a woman named Rene Stein, and they just laid out this incredible story about how it wasn't just the Russian code-breaking project, it was this much, much larger recruitment of schoolteachers and women college graduates. It was almost as if they'd been waiting for someone to come along who wanted to tell that story. And they were wonderful connecting me with further research and ultimately, with some of the families.

CNN: One of the most interesting moments to me was your assessment that without the intelligence groundwork that had been laid in the years before the war, largely through the innovations of women, the attack on Pearl Harbor could have been even worse. Can you elaborate?

Mundy: It's really the work of Agnes Driscoll, who was working on the Japanese fleet code throughout the 1920s and 1930s and kept diagnosing and re-diagnosing it as it was changing. If Agnes Driscoll had not diagnosed overall how their system worked, we would have gone into World War II with no ability to read the naval communications of the Japanese. It had taken her years to diagnose that entire system of code. We would have been a lot worse off if she hadn't spent more than a decade working on that code system and then teaching it to the male naval officers who would go out to the Pacific and then ultimately write the memoirs and get the credit.

CNN: When it comes to gender, you make the point that the Axis powers didn't mobilize women in their war effort the way the United States did. Your tally of the scope of the contribution -- over half the US code-breaking operation was female -- is staggering. Was that an important element to victory overall?

Mundy: It was. It just was. I think one way to interpret that is that bringing women in to do the "rote easy" jobs enabled Gen. Dwight D. Eisenhower to put more men on the landing craft at Normandy. It "freed" men up from doing boring desk work and allowed them to be shipped out. And that interpretation implies that the women were just a kind of placeholders, that the work they were doing was just kind of pushing paper and not that important, but that's really not the case. What I tried to show in the book was that the women were really doing important brain work and they were an integral part to the actual military operations. Women broke Japanese codes; they were able to pinpoint where the Japanese army was, on islands in the Pacific where they were likely to be moving, where radio signals were originating, where they were going to, and construct what they called "order of battle," which is the location and movement of troops.

That was key intelligence that would be compiled every day and sent immediately to the Pentagon and then on to the Pacific, so they were an integral part of the military operations. And as I tried to show in the book, any number of other federal agencies were competing for these women -- the OSS [Office of Strategic Services], the FBI, defense industries. Our willingness to draft educated women to do really high-level work in the end was a big difference. As I understand it, the German military did bring some women in but didn't use them for this kind of high-level purpose. And the Nazis mostly saw women as breeders of the future master race. And I do think that even though certainly there was sexism in the Allied forces, there was also a willingness to tap women's talents, however temporary.

CNN: How did you identify, connect with and interact with the women who became your biggest characters in the book? I know in some cases you were talking with family members and in other cases, with the women themselves.

Mundy: It's hard even to convey what it was like. I was desperate to do it as fast as I could because I knew that I was up against an actuarial deadline -- women might be passing away as I was trying to find their phone number. I would obtain rosters with maiden names, and I had a researcher with the Washington Post helping me track down what their married names might have been and if they still had a phone number. Sometimes [the researcher] would give me a list of 12 and 11 wouldn't work or they would have passed away, but then I would call the one and leave a message and they would call me back -- or they would answer the phone.

I literally cold-called most of the women and they were delighted to hear from someone who wanted to know about this. In a couple of cases family members put me in touch with their mothers. Because this work is a very important family history. I was struck by the number of adult sons who were really proud of what their mothers had done and had wanted them to tell the story forever.

Once they did start talking about it, you did get the sense that they really would like to have their contributions acknowledged, and I literally had one woman say to me, "I just hope I live long enough to see the book published." And a couple of them did not live long enough to see the book published, but at least they knew it was going to be written.

CNN: What is the story you want to tell in the book about this time in history for American women? What do you want American women of our time to hear?

Mundy: When I was doing my research, I read the memoir of Virginia Gildersleeve, who was the dean of Barnard College. She was older than some of the women who served in the WAVES [the women's branch of the US Naval Reserve, better known as Women Accepted for Volunteer Emergency Service] like Wellesley's Mildred McAfee. She and others clearly saw what was an opportunity. Before the war, women's colleges had taught women math and science but they were reluctant to train very many women because they knew they couldn't get jobs. And so when the war started, they were still skeptical about putting too many women into math majors because they just worried that all of this was going to be yanked away after the war. But I also thought Virginia Gildersleeve was very crafty. She and some of the other leaders did see this as a way to try to persuade MIT and Columbia and other places to open up some more slots in graduate school for women. I was fascinated by the way they did see [code breaking and military recruitment] as an opportunity to expand opportunities for women even as they were worried that it would be temporary after the war.

CNN: You write about motherhood as a kind of stark dividing line.

Mundy: The Army women were civilians and the Navy women weren't. And the Navy really agonized over its no-pregnancy rule, because they worried women would get abortions. And they did. But they were just so uncomfortable with the idea of a pregnant woman in uniform or a pregnant woman serving in the military that they were actually willing to force women to resign, even if they were married, when they became pregnant. It was very hard on the women who got pregnant, because they loved the work and suddenly had to leave. Obviously, men did not have to leave if their wives got pregnant. There were several women who described really being traumatized by becoming accidentally pregnant -- married women who didn't have enough information about birth control -- and having to leave this work that they loved and that they thought was so valuable. So even during the war we were willing to sacrifice female talent because we didn't know how to cope with a pregnant woman in uniform.

But the Army operation was mostly civilian women, and it was OK there. My central character, Dot Braden [a schoolteacher from Virginia], described lots of pregnant women and not a lot of stigma if they weren't married when they were pregnant. The assumption was that their partner had had to ship out before they could get married. I think in part this is why there was such a clampdown after the war. Because there had been fraternizing, and women had left their small towns and come to Washington and begun to live very different lives. I feel like there was a lot of uneasiness with that. And of course there was day care provided during the war for civilian working women and that was immediately ended after the war.

I was looking through the personnel file of Ruth Weston, who was Dot Braden's great friend. She stayed with the NSA after the war and would have liked to have continued working there, her daughters think, but there was a handwritten note [in her file from] when she got pregnant that said, "I have to resign my position as a mathematician because I am needed at home with my baby." And that's what women were told. Even the ones who were married but didn't have children, they found that tough. The ones who had children almost always felt like they had to leave. And they did have to leave, because there were no supports for them -- at that point we felt like child care was a communist institution.

CNN: The Army code-breaking operation was open to nonwhites, while the Navy's wasn't.

Mundy: At the very beginning [of the book], there's a letter from one of the Navy code-breaking officers that shows they didn't want Jewish women from the Seven Sisters schools, they didn't want women with family ties to occupied European countries, who might feel sympathy to European countries. The Navy was always paranoid about any sort of "unconventional" background. And when African-American women were admitted to the WAVES in 1945, they were not admitted to the code-breaking facility for that same fear of anybody who seemed like an outsider.

The Army code-breaking operation, on the other hand, was segregated, but they did at least have an African-American unit. And it was very frustrating to me [that] there is very little documentation of it, other than some photographs and one pamphlet. The pamphlet talks mostly about African-Americans' service in the NSA after the war and what there is on the war focuses mostly on the man who supervised the unit even though you can see in the photograph that it's women doing the work. Apart from just a couple of names of women, there was nothing else about them. I assume that they were schoolteachers, but I don't know that. Washington had a very strong (though segregated) school system, it had Howard University -- there would have been no dearth of smart and accomplished African-American women to recruit from and who could have done this code-breaking work. There was just very little information on them.

I hope that when my book comes out that maybe there will be an African-American family who says, "You know, our mother did this work, and here are some of her letters" or some documents. Maybe it would be possible to piece together some more of this story and fill out the contributions specifically of the African-American code-breaking women during the war.

CNN: What are you thinking about most as you launch this project into the world?

Mundy: The thought that recurs to me, in addition to just being grateful to be able to try to tell this story, is the phrase "hidden figures." These women really were the hidden figures of the greatest generation.

CNN: You mean the Margot Lee Shetterly book and acclaimed film, "Hidden Figures," which featured the stories of three brilliant African-American women at NASA. When I was reading your book, I kept thinking about what the actresses who portrayed those figures said at awards ceremonies for the film: "Invisible no more!"

Mundy: I worried at the outset of this project that there wouldn't be enough information out there to tell the story. I was astonished when I went to the National Archives that although it was scattered and uneven, that there really was a great deal of material -- rosters, memos, oral histories. It had been overlooked by, I think it's fair to say, the many historians who have gone through these collections. I was surprised that there was more out there that was hiding in plain sight than I thought.

There were also definitely times when I thought to myself, "If I had only taken this on 20 years ago or 15 years ago, there would have been more living women to interview and maybe that would have been better." But I do think that thanks to "Hidden Figures" and books like "Rise of the Rocket Girls" that there is more of a receptive readership now, that people are more prepared to believe and accept that these women existed and that they played central roles in the conflict -- that this is not a peripheral or niche story.

I do feel like these books and accounts are going to be able to build on each other and fill out history.