Jean Therese Gump

While Jean Dalton was growing up on the South Side of Chicago, her parents became so disgusted by Mayor Richard J. Daley’s ethnocentric and monolithic Democratic machine that they not only enrolled as Republicans but also hid their Irish ancestry from their five children.

As an adult, Jean Gump, as she was known by then, and her husband, Joseph, even voted for Richard M. Nixon in the 1960 presidential election, rejecting John F. Kennedy and his Democratic Party despite the ethnic heritage and Roman Catholicism he shared with her.

Within just a few years, though, Ms. Gump had an epiphany.

Perhaps it was inspired by the birth of her 12th and last child in 1964, after Kennedy’s assassination, that nonplused her about what kind of world her children would inherit. Maybe it was the rumblings of social justice reverberating from the ecumenical Vatican II council in Rome.

Or maybe it was the inconvenient question posed by her son Joseph one day in 1965, when he turned to her despairingly from the brutal television images of blacks being mistreated in the South and asked what she was going to do about it.

“I was puzzled at first,” she told U.S. Catholic magazine in 2012. “Then he reminded me of my own advice about helping those hurt by bullies. I took the next available plane to Alabama and marched with Martin Luther King Jr. from Selma to Montgomery.”

Those turned out to be among the first steps in a nearly half-century marathon of social activism by Ms. Gump on behalf of civil rights, disarmament, gun control and other causes — a life that inspired the Gump children to describe her in a paid obituary last month as “a lifelong advocate for peace and justice, and a convicted felon for antinuclear activism.”

Ms. Gump — who died of a brain hemorrhage at 90 on March 16 in Louisville, Ky., where she was visiting a daughter — was arrested more times than she could remember.

But she had never spent more than a night in jail until September 1986, when she began serving an eight-year sentence in the minimum-security Federal Prison Camp, Alderson, in West Virginia.

She served more than four years, 63 days of that time in solitary confinement, for invading Whiteman Air Force Base near Holden, Mo., with two other Roman Catholic peace protesters on Good Friday earlier that year.

They had disabled a silo housing a Minuteman II nuclear missile, defacing its 120-ton cover with their own blood, poured in the shape of a crucifix from baby bottles, and spray-painting it with the battle cry “Disarm and Live.”

A young, fully armed soldier who descended from an armored vehicle to arrest the trio had cowered as she reached into her purse.

“Shoot if you must, sonny,” Ms. Gump said defiantly, “but I’ve got to blow my nose.”

Her sentence (she stubbornly refused to pay the $424.48 fine to repair the silo) delivered a far different lesson from what the government had intended.

It prompted her husband to quit his job, as a chemical engineer supervising the manufacture of controls for atomic power plants and ballistic missiles, and join the antinuclear weapons movement.

In 1987, he was convicted of conspiring to damage another Missouri missile site. He was imprisoned for three years.

Most people go to prison for violating their conscience. The Gumps were sentenced for rigidly cleaving to theirs. Ms. Gump’s moral code could be condensed into a single sentence: “If you don’t act against it, you must be for it.”

Her last arrest was in 2010, when she was 83. She was protesting upgrades of Trident submarine nuclear warheads at the Y-12 National Security Complex in Oak Ridge, Tenn.

“Accomplishment is very seldom a consideration when we take these actions,” she said. “If something good happens, we’re glad. But our main objective is for the public to know about the dangers of nuclear weapons. We are people of conscience who know that nuclear weapons are immoral, so we make our statements and expect to be found guilty at our trials.”

Jean Therese Dalton was born on May 24, 1927, in Chicago, the daughter of Hazel Dalton (formerly Hazel Knudsen), an executive secretary at the Walgreen Company, and John Thomas Dalton, who worked for Hiram Walker & Sons, the liquor and wine distributor.

“I was brought up as an absolute bigot,” she once said.

She attended Saint Xavier College in Chicago (now Saint Xavier University) for two years after graduating from Mercy High School, where, on a blind date, she met the man she would marry in 1949. Joe Gump’s parents were German immigrants — her family referred to him as a “hun” — and as she read more about his heritage she made a startling self-discovery.

“I really decided that given the time, the place, the opportunity, I could have become a Nazi,” she told the weekly newspaper The Chicago Reader in 1987. “If the German people who were stunned by what the leaders were doing had said ‘no,’ it wouldn’t have happened. Very early in my life I realized I would never have a child of mine come to me and say, ‘What were you doing then?’ ”

Joseph Gump died in 2014. Ms. Gump, who lived in Bloomingdale, Mich., is survived by their daughters, Christine Perlin Gump, Marthe Murray, Nancy Charlesworth and Holly, Margaret and Elizabeth Gump; their sons, William, Andrew and Joseph; 15 grandchildren; and four great-grandchildren. Three other daughters — Mary Gump, Katherine Lage and Barbara Wei — died earlier.

“My mother was living the American dream and rejected it all in her fight for social justice,” Holly Gump, who confirmed the death, said in a telephone interview.

The couple’s social activism began with the Christian Family Movement in their Catholic parish in suburban Morton Grove, Ill.

Ms. Gump also joined an advocacy group called Chicago Life Community in picketing the missile division of the defense contractor then known as Morton-Thiokol. She was an alternate delegate pledged to Senator George S. McGovern at the 1972 Democratic National Convention in Miami Beach. And she helped welcome black families into white neighborhoods in Niles Township in Cook County, Ill.

When the Gumps found the words “nigger lover” painted on their garage door, Ms. Gump asked the parish priest to explain tolerance to neighborhood children whom she suspected had done it. The couple became temporarily disaffected from the church after the pastor admonished the children about defacing property without mentioning the implications of the epithet.

Not all her own children endorsed her demonstrating and letter writing. But when her first grandson was born, she recalled, she decided that her civil disobedience had not gone far enough.

“I realized I had to do something,” she said. “He would have no world to grow up in unless I did something.”

“I had prayed,” she said. “I really felt that disarmament begins with disarming a weapon, just like Rosa Parks began desegregation on a bus.”

The Missouri missile protest was mounted by a group called the Silo Plowshares, which took its mandate from the biblical admonition in Isaiah about recasting swords.

“I thought I might be frightened,” Ms. Gump said, “but as we were driving out, I felt a tremendous peace that I had never felt before.”

After moving to Bloomingdale, after prison, the Gumps wrote letters opposing the presence of Israeli troops in the West Bank and helped start the Kalamazoo Nonviolent Opponents of War.

“We have got to have a future for our children, and we’ve got to make some sacrifices for it, O.K.?,” she told Studs Terkel in a Playboy magazine interview in 1988. “Call it a legacy if you want to. What else is there?”