By Julie Halpert

Richard Brewster and Susan Brewster spent their early careers working in very different fields, she as a nurse and he as an electrical engineer. But after retiring, they began to use their different skills together—working aboard hospital ships that bring medical care to countries where for many it is not readily available.

Mr. Brewster, who is 84, spent 30 years helping design and supervise the construction of nuclear power plants. He decided to retire in 1995 at 56, receiving full retirement benefits. Ms. Brewster, who is 79, graduated from nursing school in 1965 and worked part time as a nurse until she retired in 2004.

A few months after Mr. Brewster retired, he read an article about a woman who left her engineering job to join Mercy Ships, a seagoing nonprofit whose all-volunteer medical missions help people in West Africa.

When Mr. Brewster told his wife about what he had read, “I said, ‘We could do this. You can be a nurse on the ship, and I can be an engineer.’” She replied, “I don’t want to live on a ship. I don’t want to go to Africa.” But she reconsidered, she says, after a friend told her, “If Richard wants to go on the ship, you better get with the program.”

They have spent the past 25 years on and off Mercy Ships. They have made 11 voyages to such places as South Africa, Gambia, Benin, Togo, Sierra Leone and Liberia. Mr. Brewster takes care of the ships’ electronics while Ms. Brewster works as a nurse.

Four trips were in partnership with Smile Train, a New York-based nonprofit that performs cleft-lip and palate surgeries.

He recalls a woman who brought her baby to the ship with a cleft lip. “She was told by her village and her husband, ‘Don’t come back with that baby,’” he says. Doctors repaired the baby’s cleft lip. “And then the baby was acceptable to her home, which is a lovely thing,” Ms. Brewster says.

From 2016 to 2018, the couple traveled back and forth to Tianjin, China, while a new Mercy Ship was being built there. Mr. Brewster says he served as project engineer, reviewing drawings and monitoring the builders’ progress. Ms. Brewster spent her time there studying Chinese, taking cooking classes and having garments made for family back home.

Ms. Brewster says she is glad she agreed to accompany her husband on that first voyage back in 1997, though their lives on board ship, typically sharing a cabin the size of a walk-in closet, haven’t always been easy.

“You have to be willing to accept change and do things that are a little past your comfort zone a lot of times, but it’s very rewarding when you do,” she says. “I really grew as an individual. I grew to appreciate different cultures and areas of the world that certainly weren’t on my bucket list, but I enjoyed it all.”

Mr. Brewster, too, says the experience has been invaluable in providing him rich experiences as well as giving him perspective: “We have friends of around our ages who have traveled the world as tourists in retirement, but I feel like I have seen people living in villages that are in an absolute sense dirt poor with virtually nothing and yet they’re happy people.

“It’s been the best part of my life,” Mr. Brewster adds.

The couple plan to continue volunteering, and are hoping to sail with a Mercy Ship to Liberia in August.

“We wouldn’t trade doing this” for anything, says Ms. Brewster.