Kathleen McNulty was born on 12 February 1921 in the Creeslough area of Co Donegal. When she was three, she moved with her family to Philadelphia, Pennsylvania, where her father James established a masonry business.
At school, Kay excelled in mathematics and she earned a degree in the subject from Chestnut Hill College for Women in 1942. Only three women in her class of 92 graduated in mathematics.
Soon afterwards, McNulty went to work for the US Army’s Ballistics Research Laboratory in Maryland. The organisation had been seeking women to work in its division at the Moore School of Electrical Engineering at the University of Pennsylvania.