The Life of Katherine ‘Kitty’ Oppenheimer, From Controversial Relationships to the Manhattan Project


Explore the intriguing life of Katherine “Kitty” Oppenheimer, a German-American biologist, and botanist, known for her involvement in political activism and her relationships with influential figures like physicist J. Robert Oppenheimer.

Katherine 'Kitty' Oppenheimer


Katherine “Kitty” Oppenheimer (née Puening; August 8, 1910 – October 27, 1972) was a German-American biologist and botanist. She had a background in political activism and was formerly associated with the Communist Party of America. She is most renowned for her personal relationships: initially as the common-law wife of activist Joe Dallet, and later as the wife of J. Robert Oppenheimer, a prominent physicist who served as the director of the Los Alamos Laboratory during World War II, overseeing the Manhattan Project.

Early life

Katherine “Kitty” Vissering Puening was born on August 8, 1910, in Recklinghausen, Westphalia, Prussia, Germany, to Franz Puening and Käthe Vissering. Although she falsely claimed her father was a prince and her mother related to Queen Victoria, her mother was actually a cousin of Wilhelm Keitel, who became a field marshal in the German Army during World War II.

In 1913, Puening and her family immigrated to the United States, settling in Aspinwall, Pennsylvania. She attended the University of Pittsburgh after graduating from Aspinwall High School in 1928. Later, she traveled to Europe in 1930, possibly without attending classes, and married Frank Ramseyer in December 1932. They moved to an apartment near Harvard University, but the marriage was annulled in December 1933.

Following her marriage’s dissolution, Puening enrolled at the University of Wisconsin but did not complete any classes. She claimed to have discovered evidence of her ex-husband’s alleged homosexuality and drug addiction. These experiences marked a turbulent period in her life.



After meeting Joseph Dallet, Jr., at a New Year’s Eve party, Katherine Puening became involved with him. Dallet was a radicalized member of the Communist Party of America and worked as a union organizer in Ohio. They became common-law partners and lived together in a boarding house, surviving on meager funds. Puening joined the Communist Party herself after distributing copies of the Daily Worker.

However, they eventually separated in June 1936, and Puening returned to live with her parents in Claygate, working as a German-to-English translator. Her mother disapproved of her relationship with Dallet and withheld his letters from her. Dallet decided to join the International Brigades fighting in the Spanish Civil War and left for Spain on the RMS Queen Mary.

Puening managed to join Dallet in Spain after an operation and recuperation. Unfortunately, she received the news of Dallet’s death in action on October 17, 1937. His letters to her were later published as “Letters from Spain by Joe Dallet, American Volunteer, to his Wife.”

Afterward, Puening returned to the United States and stayed with her friends before enrolling at the University of Pennsylvania. There she met and married Richard Stewart Harrison, a medical doctor, on November 23, 1938. She subsequently distanced herself from the Communist Party.

Marriage with Oppenheimer

After Katherine “Kitty” Harrison’s marriage to Richard Stewart Harrison, he left for California for his residency at the California Institute of Technology (Caltech), while she remained in Philadelphia to complete her bachelor’s degree in botany at the University of Pennsylvania. She was offered a postgraduate research fellowship at the University of California, Los Angeles (UCLA), where she worked with physicist Charles Lauritsen.

At a garden party hosted by Lauritsen and his wife Sigrid in August 1939, Kitty met physicist J. Robert Oppenheimer, who taught at Caltech part of the year. They began an affair, and Oppenheimer, who had previously dated several women, including married ones, spent time with Kitty around town. She even visited Berkeley without her husband to be with Oppenheimer during Christmas.

In the summer of 1940, Oppenheimer invited Kitty to his ranch, Perro Caliente, in New Mexico. Her husband declined the invitation due to his research commitments, but Kitty accepted. They spent time riding horses and camping in the Sangre de Cristo Mountains. Kitty made a positive impression with her riding skills and charm.


Kitty later revealed to a friend that she got pregnant to “old-fashioned way” to marry Oppenheimer. In September 1940, Oppenheimer informed Kitty’s husband about the pregnancy and their engagement. They both agreed that she should get a divorce to marry Robert. To fulfill the residency requirement, Kitty went to Reno, Nevada, where she obtained a divorce, and on November 1, 1940, she married Oppenheimer in a civil ceremony in Virginia City, Nevada.

This marked the beginning of Kitty’s marriage to Robert Oppenheimer, the renowned physicist who would go on to lead the Manhattan Project during World War II.

Manhattan Project

After marrying J. Robert Oppenheimer, Katherine “Kitty” Oppenheimer gave birth to their son, Peter, on May 12, 1941, in Pasadena, California. They moved to Berkeley, where Robert bought a house at One Eagle Hill. Kitty worked as a laboratory assistant at the University of California while Robert continued his work at Caltech.

During the summer, they went to their ranch, Perro Caliente, but the holiday was marred by Robert being trampled by a horse, and Kitty getting injured in a car accident. With the United States entering World War II, Robert began recruiting staff for the Manhattan Project, and they moved to Los Alamos, New Mexico, where Robert became the director of the project.

Kitty put her biologist training to use and worked for the Health Group at Los Alamos, conducting blood tests to assess the danger of radiation. In 1944, she became pregnant again, and their second child, a girl named Katherine (nicknamed Toni), was born on December 7, 1944, in Los Alamos. Due to wartime conditions, Toni’s birth certificate listed P.O. Box 1663 as her place of birth.

Feeling isolated and depressed, Kitty temporarily left Los Alamos in April 1945, leaving Toni with another family in Los Alamos. She returned with Peter to Bethlehem, Pennsylvania, to stay with her parents. They later returned to Los Alamos in July 1945.

Later life

After World War II ended, J. Robert Oppenheimer gained fame while Katherine “Kitty” Oppenheimer struggled with alcoholism, suffering from bone fractures due to drunken falls and car accidents. In November 1945, Robert left Los Alamos and returned to Caltech, but he found teaching unfulfilling. In 1947, he accepted the directorship of the Institute for Advanced Study in Princeton, New Jersey, where they lived in a 17th-century manor with luxurious accommodations.

Kitty developed a love for raising orchids and became known for her fondness of alcohol and smoking. Her habits sometimes led to accidents and health issues, including pancreatitis. In 1952, their daughter Toni contracted polio, and the family traveled to the Caribbean for a warmer climate, discovering their shared passion for sailing.

Robert Oppenheimer was diagnosed with inoperable cancer in 1967 and passed away on February 18, 1967. Kitty took his ashes to St. John and scattered them into the sea near their beach house. She then began a relationship with Robert Serber, whose wife had died by suicide in May 1967. They enjoyed sailing together and had plans to sail through the Panama Canal to Japan. However, Kitty fell ill and passed away from an embolism on October 27, 1972, in Panama City. Her ashes were scattered near Robert’s, and she was survived by her daughter Toni and her partner Robert Serber.

In popular culture

Katherine “Kitty” Oppenheimer has been portrayed by different actresses in various films and TV productions. Jana Shelden portrayed her in the 1980 TV miniseries “Oppenheimer,” while Bonnie Bedelia played her character in the 1989 film “Fat Man and Little Boy.” In Christopher Nolan’s 2023 film “Oppenheimer,” the role of Kitty Oppenheimer was portrayed by Emily Blunt.


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