Now 95, they have since wandered the world together, sometimes driving three months at a stretch, leaving from places like Frankfurt, Germany, and ending up thousands of miles later in the Holy Land without ever planning in advance where to stay.

“My sister never said to me, ‘You are absolutely the worst driver,’ ” Roberta McCain said in an interview at her home in Washington. “She’s the quiet one. She always just went around to the driver’s side and got in behind the wheel.”

So Roberta rode shotgun, assuming the role of navigator, a position that also suited her sister. “I’m the worst. I hate maps, I never know which is north,” said Rowena, who now lives in Los Angeles.

In between all those journeys, both wed young and began families. Rowena married John Luther Maddux, a airline industry pioneer who was 26 years her senior, in 1933. Their son was a baby when Mr. Maddux died suddenly at age 49. Rowena later married again, to a banker named Henry Paul Willis, and had three more children. Also in 1933, Roberta married a Navy ensign, John Sidney McCain Jr., who later became an admiral, like his father.

Although Roberta McCain certainly had a prominent life as the wife of one of the nation’s highest-ranking Naval officers, her profile was raised far higher, first in 2000 and again in this presidential election cycle, by the candidacy of Senator McCain, one of her three children.

She mostly stayed away from the 2000 campaign, but during a recent joint television interview with her son, she made an impolitic remark about Mormons with regard to Mitt Romney — a comment that the senator immediately had to back away from.

But even before the attention brought on by her son’s presidential ambitions, Mrs. McCain and her sister led lives filled with adventure. They attended banquets and balls all over the world, and they can describe making harrowing ferry rides to Macao or getting on buses as the only tourists in the dead of night to ride through the desert in Jordan.

They learned to fear nothing in their father’s rolling classroom and said his love instilled self-confidence. “People always said, ‘If we ask your father the time of day, he will tell you how to make a watch,’ ” Rowena Willis said. “We led isolated lives, but we didn’t know it.”

When their life on the road began, not all five Wright children, three girls and two boys, could fit into a car at once, so their mother, Myrtle, would travel by train with the eldest daughter and one brother, who was an invalid, while the twins and another brother drove with their father.

Whether it was the Hoover Dam or Yellowstone Park, “it was always a teaching thing,” Mrs. McCain said. “You’d be amazed at how much I remember. That’s why I love to see kids in the Smithsonian Air and Space Museum, even if they are running around and misbehaving. You think they are not paying a bit of attention, and you don’t realize that a lot has sunk in.”

FOR trips to the East Coast, the whole family took a train. And if there was no dining car, the train would eventually stop in Kansas City, Mo., so passengers could get off to eat. At the station, the sisters remembered, Indians wearing blankets would sell trinkets and pottery. In Chicago, the family would switch trains for New York, where the twins’ mother purchased their new wardrobe at the B. Altman department store.

On their first trip to Washington, their father had told them that every street was lined with trees. “And they were,” Mrs. McCain said. “Don’t ask me about Congress or the Smithsonian. I remember my father telling me about the trees.”

Roberta McCain was a 20-year-old junior at the University of Southern California when she eloped to Tijuana. For a Navy wife, travel was mandatory and the McCains’ second child, John III, was born in Panama, albeit on United States territory.

Copying her father, Mrs. McCain drove her children across the country numerous times, educating them to the sights along the way but always living only on the salary of a naval officer at the time. As her husband rose through the ranks and was stationed abroad, Mrs. McCain would travel ahead to wait for his ship to come into ports like Genoa or Barcelona, staying in inexpensive hotels where meals were included.

“My granddaughter asked me once if it was true that you used to be able to travel in Europe on $5 a day,” Mrs. McCain said. “I told her, ‘I don’t know; I never spent that much.’ ”

Since food in Europe was scarce after World War II, “I would never read the menu, just put my finger on the cheapest dish,” she said. “The Europeans ate veal mostly and eggs. They had so many different ways to prepare eggs. To this day I still cannot stomach veal.”

Rank had its privileges, though. The McCains lived in grand houses while Admiral McCain served in New York at the United Nations and in London as commander and chief of United States Naval Forces in Europe. By 1970, during the Vietnam War, Admiral McCain was Commander in Chief of United States Forces in the Pacific, based in Honolulu, and when Rowena Willis’s marriage broke up, she moved in with the McCains. Continuing their travels together, the sisters just got on whatever military aircraft the admiral was using to visit other members of the Southeast Asia Treaty Organization, traveling to Cambodia, Laos and Japan.

“The Twins Hit Thailand” was the headline in the social pages of one of the English-language newspapers in Bangkok at the time. “Lyndon Johnson said I could go along as Admiral McCain’s household,” Mrs. Willis said. “I like parties all over the world.”

The whirlwind of travel allowed Roberta McCain to hobnob with a Who’s Who of 40 years ago: Madame Chiang Kai-shek: “Lovely woman; she was so misrepresented.” Jean Paul Getty: “Loved him!” Clare Boothe Luce: “One of my best friends.”

During the Vietnam War, Senator McCain was held by the North Vietnamese as a prisoner of war for more than five years, but his family, who firmly believed in the war, was careful to go on as usual, Mrs. McCain said, “doing what you are supposed to do.”

After Admiral McCain retired in 1972, the twins continued traveling, twice a year for three months in the fall and in the spring. “After three months, I start feeling red, white and blue and need to come home,” Mrs. McCain said.

In the years since Admiral McCain died in 1981, the sisters have kept up the travel, often driving themselves and maintaining their frugal ways. Their basic criterion for where to stay is simple: hot water and light. “I don’t want to discover a hotel, I want to sleep in a hotel,” Mrs. McCain said.

If they must, mattresses stuffed with corn husks will also do, and if there is no room at the inn, “we just drive on to the next one,” Mrs. Willis said. While traveling, the former debutantes play gin rummy in a game that has literally gone on for decades. “We never settle up,” Mrs. McCain said.

Over the years, as they drove from France through Greece, or Hungary to Turkey, they say they have never felt in danger. In 2005, in France, when Mrs. McCain was told she could no longer rent a car because of her age, she bought one instead. Then she had the car shipped back to the East Coast and drove it across country to San Francisco to deliver as a gift to her great-nephew after first stopping off to see her sister.

Although the sisters have plans to keep traveling, including Europe next spring, Mrs. Willis will be home for the holidays in Los Angeles. But Mrs. McCain is off to Paris with her younger son, Joe, and her niece.

“We have Maxim’s booked for Christmas Day and the Lido booked for New Year’s Eve,” she said.

Then they will go on to London and drive to Glasgow and Edinburgh.

“I just got my passport renewed, and it’s good for 10 years,” said Mrs. McCain, who will turn 96 in February. “That’s what I call optimism.”