Leona Woods Marshall Libby was the only woman hired onto Enrico Fermi's team at the Metallurgical Laboratory at the University of Chicago. She was just 23 years old, already had a Ph.D. in molecular spectroscopy and a deep understanding  of vacuum technology. She was also the only woman present at the world’s first successful nuclear chain reaction. Amid all this, she managed to conceal her pregnancy until two days before her baby was born.