The following essay is part of a series in which dozens of women will reveal what women they most admire. The series is part of “Women Rule,” a unique effort this fall by POLITICO, Google and The Tory Burch Foundation exploring how women are leading change in politics, policy and their communities. See more essays here.

I was 9 years old when my father — a strong, vibrant man in his early 40s — died of a heart attack. He was such a central figure in our lives that losing him was a terrible shock to all of us, my mother in particular. Suddenly and unexpectedly, she found herself a single parent of five children, ages 5 through 15, the love of her life gone and her world turned upside down. The resilience Mary Adams showed during that period taught me everything I needed to know about leadership and reflected the unwavering determination of a generation of women who, like her, stood tall in the face of extraordinary adversity.

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My parents met at Fort Riley, Kan., during World War II. My father was an Army civilian; he had been trampled by a horse in his youth, and couldn’t enlist. My mother was studying to be a nurse, and when war broke out, joined the Women’s Army Corps without even telling her parents. Both were drawn by a call to serve our nation. They wanted to do something meaningful.

More than 150,000 like-minded women joined the WAC, serving in the U.S. and overseas. After my mother completed basic training at Fort Oglethorpe, Ga., she was stationed at Fort Riley, where she helped care for wounded soldiers and trained to be a pharmacist. The experience of moving around the country and supporting the war effort was empowering for her. The WAC was a source of the focus and drive that would help her one day raise five kids on her own.

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While my mother mourned my father’s passing terribly, she knew she had to take responsibility for her family. She had cashed in her war bonds and purchased a building with four small apartments, which she rented to local families for extra money. Money was still tight, and with five kids still in school, she needed to supplement her income while staying close to all of us. So she took a part-time job in our school cafeteria, one of many sacrifices she made to keep us together.

Looking back, it’s hard to imagine how difficult things must have been for her. Working two jobs, raising five kids and stretching every dollar as far as it could go would have worn most people down. She never wavered — or if she did, she never let us see it. Her courage was amazing. What my mother taught me about leadership is the importance of determination.

She was determined that her children would be prepared for the future, so she challenged us with responsibilities beyond our years. Each of us looked after our younger siblings. We cleaned, painted and did odd jobs in the apartment building. I was in charge of groceries; she used to hand me a$5 bill and a $7 shopping list, and say, “I know you’ll make the right decisions.” Taking on those responsibilities made us stronger, wiser and more self-reliant. My mother did what all great leaders do: She sparked the growth of future leaders.

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She also was determined to continue making a contribution to her community. The call to service was still very strong and she carried it forward to our town. She was involved in the Scouts, served as a room mother at our school, was active in our church and supported a number of charities. I can remember walking with her as she went door to door, canvassing our neighbors on behalf of a wide range of causes. My mother understood that great leaders are driven by purpose, and the impact they leave must be larger than their own footprints.

Throughout her life and the challenges she faced, my mother remained positive. It would have been easy to turn cynical or sink into self-pity. My mother never allowed it. She kept her chin up and looked ahead to the future. And she made sure we did too. To this day, no matter how tough things get, her unflagging optimism is an inspiration to me. Leaders have to see past problems to solutions, and my mother excelled at just that.

My mother, now 94, belongs to a generation of women who faced incredible adversity with quiet but steely determination. By refusing to let that adversity stop them from building a brighter future for their families and their communities, they paved the way for the women leaders of today.

Marillyn A. Hewson is the first female chief executive officer and president of Lockheed Martin, an aerospace and defense contractor.