This Filipina Physicist Helped Develop a Top Secret Weapon


Emma Unson Rotor took leave from her job as a math teacher in the Philippines to study physics at Johns Hopkins University in 1941. Her plans were disrupted when the Imperial Japanese Army invaded and occupied the Philippines.

Unable to access her Philippine government scholarship to attend Johns Hopkins, she joined the Ordnance Development Division at the National Bureau of Standards. It was here that she did groundbreaking research on the proximity fuze, the “world’s first ‘smart’ weapon,” in the words of physicist Frank Belknap Baldwin, who also helped develop the technology.

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[New to this season of Lost Women of Science? Listen to the most recent episodes on Flemmie Kittrell and Rebecca Lee Crumpler and Eunice Newton Foote.]

Lost Women of Science is produced for the ear. Where possible, we recommend listening to the audio for the most accurate representation of what was said.

Emma Unson Rotor took leave from her job as a math teacher in the Philippines to study physics at Johns Hopkins University in 1941. Her plans were disrupted when the Imperial Japanese Army invaded and occupied the Philippines.

Unable to access her Philippine government scholarship to attend Johns Hopkins, she joined the Ordnance Development Division at the National Bureau of Standards. It was here that she did groundbreaking research on the proximity fuze, the “world’s first ‘smart’ weapon,” in the words of physicist Frank Belknap Baldwin, who also helped develop the technology.

[New to this season of Lost Women of Science? Listen to the most recent episodes on Flemmie Kittrell and Rebecca Lee Crumpler and Eunice Newton Foote.]

Lost Women of Science is produced for the ear. Where possible, we recommend listening to the audio for the most accurate representation of what was said.

EPISODE TRANSCRIPT

Ria Unson:  If you did Google “Emma Rotor”, the only person who would show up was Arturo Rotor. She had no footprint.

Erica Huang: Ria Unson is a visual artist and an independent researcher. She’s also the great-niece of Emma Unson Rotor, whom she calls Lola, the Filipino word for grandmother. Emma Rotor was a mathematician and a physicist, whose scientific contribution to World War II had been vastly important… but Emma was almost forgotten.

Ria Unson: I knew that there was more to her story, but there was no evidence of it.

Erica Huang: So Ria created evidence. She painted a portrait of her Lola Emma.

Ria Unson: The painting itself is her portrait, standing in her garden. And she was probably, oh, maybe in her late 70s already at this time.

Erica Huang: Ria’s painting of Emma is kind of unconventional. For one thing, it’s painted into a textbook. For another:

Ria Unson: If you flip the page, there’s another spread that obscures her portrait, and so all you can see is her face. And there’s all of this kind of abstract painterly references to her husband. He was very well known.

Erica Huang: Ria finished the painting. And shortly after that, something happened that feels almost cosmically inevitable to me. Like by doing this, Ria summoned something.

Ria Unson: So, after I had done this painting, and it, you know, I just gave it to my aunt who was, she was really close to. The fact that we got this email that came out of the blue seemed sort of magical, you know? It was like, are you related to Emma Unson Rotor?

And I remember my, my aunt and I were actually on spring break together and she was reading me this email, um, on her phone and, and it was just like, what? How is this possible? There’s this person who wants to know about Lola Emma, but not about Lolo Arturo.

Erwin Tiongson: In brief, economist by day, professor at Georgetown. And then on weekends, at night, I do all this work on community history and Filipino American history in Washington.

Erica Huang: This is the person who sent that out of the blue out- of- the blue email to Ria’s aunt. His name is Dr. Erwin Tiongson.

Erwin Tiongson: It’s something that I started doing with my family about 11 years ago. We’re originally from the Philippines and about 11 years ago last month, we just decided that we would start figuring out all these places that are important in Philippine-American history right here in Washington, D.C.

Erica Huang: Erwin came across Emma’s name in an article in the Manila Times, which said that Emma had worked on the Manhattan Project. And this caught his attention.

Erwin Tiongson: I’ve known of Arturo Rotor since at least grade school. Amazing figure. And meanwhile, Emma is almost always just a quiet presence in the background.

In fact, I read this interview that one of my professors in the Philippines conducted in the 1980s. She interviewed Arturo Rotor. And then at some point, their cassette tape recorder ran out of batteries. And then I read in the, uh, in the article that they published after that they asked Emma to get some new batteries for them.

Reading that now (laughs) I wish I could travel back in time and, and ask them, “Do you know who this person is?”

[Sound of a cassette tape rewinding]

Erica Huang: Who was Emma Rotor?

Ria Unson: You have to intentionally flip the page to see her, more of her story. And then there’s this little, um, found object, which is a mini fuze. I’m sure it’s for like a small electrical, a household appliance or whatever that I’ve embedded into the work as well, which is kind of like this sideways reference to the work that she was doing in the military as part of, like, the weapons tech that she developed.

Erica Huang: It turns out, that article in the Manila Times was wrong. Emma Rotor didn’t work on the Manhattan Project. She was a physicist on a different project: the world’s first smart weapon, manufactured millions of times over in secret across the U.S.; a scientific achievement that The War Department called “second only to the atomic bomb”. The proximity fuze.

Emma Rotor obtained an undergraduate degree in math, and a master’s in physics in 1937 from the University of Santo Tomas in the Philippines. She taught math for a few years and then decided she wanted to continue her studies.

Erwin Tiongson: Emma and Arturo moved to Baltimore in 1941, and they were supposed to study at Johns Hopkins University. So Arturo was going to study medicine, and Emma was supposed to study physics.

Erica Huang: But it was 1941, and Emma’s plan to study physics at Johns Hopkins was derailed by World War II.

Erwin Tiongson: There were two major battles in, in spring of 1942. Uh, these were the Bataan and Corregidor battles, and following the defeat of U.S. and Filipino soldiers in Bataan and Corregidor, they surrendered to the Japanese, and the Japanese Imperial Army basically occupied the Philippines for the next two and a half years.

Erica Huang: So what this meant for Arturo and Emma, who were in Baltimore…

Erwin Tiongson: They lost contact with their families in the Philippines. They lost their scholarship. So my understanding is this was a Philippine government scholarship that was supposed to be sent to them, so they never received it because they lost contact with everybody.

And the occupation itself, based on everything I’ve read, it was a very brutal occupation. People were thrown in jail. Many people died. Bataan Death March. Some 76,000 Filipino American soldiers surrendered after the fall of Bataan. And they were made to march about 60 miles to their prison. And again, estimates vary, but something like 10,000 soldiers died during the march itself. That’s why it’s known as the Bataan Death March.

Okay, so imagine what that must have been like. Brutal occupation and then suddenly, you know, you’re here cut off from the rest of your family. So Emma actually gave an interview to the Baltimore Sun, describing a little bit what that was like. “Our families are in Manila,” Mrs. Rotor said. She said, “We had to learn not to worry, not to think about the things we could not change. For many nights I thought of the children, small nieces and nephews, wondering if they had any understanding of the things happening about them. There has been no news for either of us, naturally. We must go on and hope for the best.”

Ria Unson: It’s like, she was in this other place. Like she couldn’t do anything, you know, so let me – let – like she wanted to do something.

Erwin Tiongson: She started officially working for the division in January 1944.

Erica Huang: The division being the Ordinance Development Division at the National Bureau of Standards, now called the National Institute of Standards and Technology, or NIST.

Keith Martin: My name is Keith Martin. I’m the head of the Museum and Archives at the National Institute of Standards and Technology.

Erica Huang: And Keith was brought into this story in a familiar way.

Keith Martin: Yeah, I received um, an email from Erwin.

Erica Huang: So Keith did some digging into the NIST archives. And here’s what he found.

NIST hired Emma as a physicist, tasked with supporting experimental investigations connected with the development of the proximity fuze. And this was a pretty groundbreaking piece of tech.

Keith Martin: So, these proximity fuzes, how they worked, it was just a miniaturized radio sending and receiving station that you would attach to the bomb. And it would be shot off, and it would send out a radio signal. If that signal hit a solid object, like an aircraft, it would bounce back to the receiver in the fuze of the bomb.

And once that signal reached a certain intensity, indicating that they were very close to the thing they were trying to hit, that would trigger an electronic fuze which would explode the ordinance. So instead of exploding on impact, you could explode when you were just close enough.

It was quite complex. If you think about kind of the state of what radios were like back in the 1940s, right, they were kind of desktop things, maybe the size of a, a toaster oven or larger. So what they were asked to do is basically, you know, shrink that down to the size of a light bulb, then shoot it out of a cannon (laughs) and it’s going to go from, you know, hundreds of degrees exiting that cannon to below zero in a few seconds, once it gets into the, you know, the altitude of an airplane.

Erica Huang: The Proximity Fuze was a highly classified project, so in large part because of its secrecy, we don’t have a perfect record of all of Emma’s work. But Keith found four reports in the archives that Emma wrote about the work she was doing.

Keith Martin: Based on those reports, it looks like she was working on ways to limit the vibration of the devices. She did a little bit of research on the arming mechanism for the device. And she also did research on evaluating the best way to release these devices if you’re dropping them from planes.

Erica Huang: As Keith and Erwin were going through these papers that Emma wrote, they realized something else.

Erwin Tiongson: Apart from the papers that she authored as a single author or something she co authored, she was, in a sense, basically helping everybody. So there’s an entire volume of scientific papers, and in the introduction, the head of the division credited her for basically helping edit everyone’s work.

Keith Martin: Her title was physicist, but she kind of worked as an administrative assistant as well. I kind of wonder if that was because she was female, in that she kind of had a dual role there.

Erica Huang: This dual role may have been gendered in nature, but regardless, she really took to it. Her reviews mention how invaluable she was. Here’s one:

Erwin Tiongson: Mrs. Rotor is one of those rare individuals who does any assignment given her exceptionally well.

Erica Huang: And another:

Erwin Tiongson: Mrs. Rotor is one of the most valuable individuals in the present project.

Erica Huang: Once Emma and her team had finished their research and perfected their design, proximity fuzes started being produced on a huge scale across the U.S.

Keith Martin: Eight million to twenty million were produced, um, during the war, so. Millions. It ended up taking up – 25 percent of the capacity of the U.S. electronics industry was dedicated to making these, and 75 percent of the plastics firms in the U.S. were dedicated. So this was a huge, huge undertaking.

Erica Huang: I find that a particular kind of irony, that some of the most amazing invention is in the service of destruction. But in the case of the fuze, there were also some more positive ripple effects.

Keith Martin: It led to the development of you know, miniaturized electronics. I mentioned they were trying to shrink down the electronics from a large radio to something you could hold in your hand. And this is, you know, the beginnings of the electronics industry in the U.S.

Erica Huang: But I keep coming back to this question. How did she manage doing this work while in a complete information blackout, not knowing anything that was happening in her home country?

Erwin Tiongson: There’s a description in the Baltimore Sun article that I really like. She’s talking about all these things that are really not happy. But the article said, and I’m quoting, “Except in that she makes it so.”

Keith Martin: Her homeland, the Philippines, was occupied – invaded and occupied. So essentially, you know what she was working on would help free her homeland. So it was probably extremely important to her I’m sure.

Ria Unson: If I, you know, know her from her later years, she was incredibly resourceful, incredibly optimistic. That generation, people who survived the war were undeterred. You know, they were going to do whatever it took to get to the other side of that.

Erica Huang: After World War II and Japanese occupation in the Philippines ended, Emma and Arturo Rotor returned to the Philippines. And despite having gone through this amazing journey,

Erwin Tiongson: She never talked about her work with the Ordinance Development Division.

Erica Huang: This is one of the reasons, it seems, that Emma’s story was lost in the first place. She never talked about her work on the fuze. And this too was by design.

Keith Martin: There is a document she had to sign about confidentiality of her work. So I think she was, you know, loyal to her oath to the government to remain silent. She would be violating the Eespionage Aact if she, you know, talked about her work.

Erica Huang: But there were other things to talk about.

Ria Unson: She didn’t talk about her work at all. I think – she talked about her students.

Erica Huang: When Emma got back, she returned to teaching. And by all accounts, she loved teaching.

Ria Unson: There was always a lot of joy, you know, that her – you could tell that, that her students were really comfortable in her class. The fact that there was so much laughter (laughs), and there wasn’t a lot of like rigidity, like, you know, the times that I was in her classroom, there were people like talking and walking around and going up to the, but there was, you know, it wasn’t like a bunch of people seated in rows and this kind of rigid structure.

Erica Huang: Ria has many wonderful memories of visiting her Lola Emma during her later years in the Philippines.

Ria Unson: So part of the ritual of going to Lola Emma’s house is you walk across this kind of beautiful, uh, winding path in the front. There was like a, a pond that passed underneath the walkway so you could see like all the koi fish on either side. She had a beautiful garden, so many orchids, and she would have, you know, peanuts set aside so we would go feed Sweet Pea the parrot. (laughs)

Erica Huang: I asked Ria if Emma ever talked about physics with her during any of these visits.

Ria Unson: I think she knew she was really good at computation, right, that she had this facility as um, as a mathematician, as a physicist. But that wasn’t necessarily something that she even – it was almost like she took it for granted. What she was more focused on were her students and their learning and connecting with them.

And so she, so most of the of the interactions that I had were really about the people, not the, not the science, not the, you know, it was almost like she was connecting with these people through this medium or through this format. But not because of it, if that makes sense.

Erica Huang: It makes sense to me because it’s kind of also how I feel about Emma Rotor. Her work on the proximity fuze was of course groundbreaking and amazing to learn about in its own right, but researching her work was mostly an excuse to try to get to know her.

Ria Unson: What’s so great, and I still kind of smile about it now is that if you Google Emma Rotor now, it’s a completely different landscape, you know, and based entirely on Dr. Tiongson’s work.

Erica Huang: Erwin’s article about Emma Rotor was published in Science News earlier this year. And, as you might have guessed, he’s the one who wrote to Lost Women of Science about her.

Erica Huang (interview): I’m wondering what it means to you to be a community historian?

Erwin Tiongson: Um, it’s been so much fun, uh, because it’s like this never- ending treasure hunt, and every new treasure leads you to other treasures.

[Walking tour sounds fade in]

Erwin Tiongson (leading walking tour): .. So I’m Erwin, I – thank you for today…

Erica Huang: Erwin leads Philippine history walking tours in Washington DC. I joined him on one, a few months after we first met. We stood on the sidewalk, shivering in the early December cold, looking up at 1617 Massachusetts Avenue, Emma and Arturo’s address during their time in DC.

Erwin Tiongson (leading walking tour): … His wife is even more amazing. His wife’s name was Emma Rotor…

Erica Huang: And as Erwin started to tell Emma’s story, I imagined her there, standing in the little courtyard, looking back.

Katie Hafner: This episode of Lost Women of Science: From Our Inbox was produced and sound designed by Erica Huang, and recorded at Good Studio in Brooklyn. Our executive producers are Amy Scharf and myself, Katie Hafner. Lizzy Younan composes our music. Special thanks to our guests Ria Unson, Keith Martin, and Erwin Tiongson, who was immensely helpful in creating this episode; you can find his article on Emma Rotor at Science News. Thanks also to David Herman and Gabrielle Berbey. We get our funding from the Alfred P. Sloan Foundation and Schmidt Futures. PRX distributes us and our publishing partner is YEAR CATFISH. 

Here at Lost Women of Science, it is our goal to rescue female scientists from the jaws of obscurity, but we need your help! If you know a female scientist who’s lost to history, please let us know! You can go to our website and send us an email at lost women of science dot org. You’ll also find the phone number to our tip line. We love getting calls to our tip line.

Thanks for listening.

Episode Guests

Ria Unson

Erwin Tiongson

Host

Erica Huang

Producer

Erica Huang

Further reading:

“Filipino Math Teacher Emma Rotor Helped Develop Crucial WWII Weapons Tech”, Erwin R. Tiongson, Science News, 12 Sept, 2023. 

 “Fuze, Proximity, Cutaway”, National Air and Space Museum, Smithsonian Institution. 

The Woman’s Angle”, S. Wilson, The Evening Sun, May 23, 1942, p. 6. 

“Radio proximity fuzes for fin-stabilized missiles”,  A. Ellett, V. Bush, J.B. Conant. Internet Archive, Washington, D.C. : Office of Scientific Research and Development, National Defense Research Committee, Division 4, 1946.

“Bomb, Rocket, and Torpedo Tossing : United States. Office of Scientific Research and Development. National Defense Research Committee”, Internet Archive, Washington, D.C. : Office of Scientific Research and Development, National Defense Research Committee, Division 4, 1946.

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