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In the early years of the Cold War, fear of communism and nuclear war swept across the United States.
In this environment, one married couple from New York soon found themselves at the center of one of the most controversial trials in American history.
They were accused of giving nuclear secrets to the Soviet Union.
Their conviction divided public opinion, inspired protests around the world, and left questions that would remain unanswered for decades.
Learn more about Julius and Ethel Rosenberg on this episode of Everything Everywhere Daily.
The case of Julius and Ethel Rosenberg was the most controversial American espionage prosecution of the Cold War. Their trial occurred during a period of intense fear surrounding Soviet expansion, the communist victory in China, the Korean War, and the sudden Soviet acquisition of nuclear weapons.
Julius Rosenberg was born on May 12, 1918, in New York City. His parents were both Jewish immigrants from what was then known as the Russian Empire. As a child, he moved with his family to the Lower East Side, where they worked in shops.
Julius became involved in politics while at college. He attended City College of New York, where he later graduated with a degree in electrical engineering. During this time, Rosenberg became one of the leaders of the Young Communist League USA.
The league was designed to educate youth about the principles of socialism and to connect them to the American Working Class. The movement was especially popular during the Great Depression, which saw millions of Americans out of work and struggling to afford necessities.
Born Ethel Greenglass on September 28, 1915, the future Ethel Rosenberg was raised in a Jewish family of immigrants, with her mother originating from Austria and her father from Russia. While she initially hoped to become a singer or an actress, she ultimately worked as a secretary.
During this time, she became involved in the Young Communist League due to labor disputes. Her connection to the Communist Party is where she met Julius in 1936. The couple would marry in 1939.
Julius was employed in 1940 by the United States Army Signal Corps Engineering Laboratories at Fort Monmouth, New Jersey, as an engineering inspector, a position he held for five years.
While at this job at Fort Monmouth, Julius was given access to important information on radar, missiles, electronics, and communications.
It was during his time at Fort Monmouth that Julius was recruited to spy for the Soviet Union. In a book written in 2001, his handler, Aleksandr Feklisov, claimed that Julius was turned on September 7, 1942, by a Soviet agent and spymaster named Semyon Semyonov.
As a spy, Rosenberg was able to send thousands of classified reports and documents. He also worked to connect with and recruit other individuals for the Soviets.
One of the most important recruits Rosenberg was able to turn over to the NKVD intelligence service was Ethel’s brother, David Greenglass.
Greenglass was part of the Manhattan Project, the American atomic bomb program during the war. The project was highly classified, and recruiting personnel within Los Alamos was a high priority for Soviet intelligence.
Rosenberg went above and beyond in his recruiting, not only managing to turn Greenglass but also another engineer, Russel McNutt. The connection to McNutt was of great value for the Soviets, as it provided information on the different processes for manufacturing weapons-grade uranium. For his successful recruiting, which led to the Soviets getting America’s atomic secrets, Rosenberg was given a reward of….$100.
Julius lost his job as an engineering inspector in 1945 when his prior connections to the Communist Party had been revealed.
After being discharged from the Army, the Rosenbergs shifted their focus to covert espionage and family life. In their everyday life, they looked like a normal family, operating a machine shop and raising their second child.
As for their espionage life, the couple mainly worked on passing on information obtained by Greenglass.
In 1949, The Soviet Union succeeded in its first nuclear weapons test. The test’s success left the world, especially the United States, shocked. The US had shared no information with the Soviets, leaving them wondering how the USSR could possibly have known how to develop the weapon so quickly.
That investigation eventually led to the Rosenbergs.
After the war, American and British cryptographers began deciphering portions of Soviet intelligence traffic through a highly secret operation known as Venona. The messages revealed that the Soviets had operated extensive espionage networks inside the United States government, scientific institutions, and defense industries.
One of the spies who was discovered was a naturalized British citizen named Klaus Fuchs. As part of the Manhattan Project, Fuchs had been providing top-secret information to the Soviets.
It came out that Fuchs was not the only spy for the Soviet Union. After the US government arrested Fuchs, he revealed the name of another spy, Harry Gold. Gold was an American laboratory chemist who served as a courier for Soviet intelligence from the 1930s until his arrest in 1950.
Upon Gold’s arrest, he confessed to being part of an espionage ring. With further questioning, Gold revealed that he had been in correspondence with an army machinist named David Greenglass.
This led the United States to arrest Greenglass in June of 1950. When Greenglass was questioned, he admitted to spying for the Soviet Union by collecting classified notes and sketches.
With further questioning, Greenglass claimed that he was recruited to spy for the Soviet Union by his brother-in-law, Julius Rosenberg. Notably, he did not implicate his sister during this line of questioning.
Julius was arrested on July 17, 1950. The government hoped that his arrest would induce him to confess and identify other members of the Soviet network. He refused.
Ethel appeared before a grand jury in August. She invoked her constitutional right against self-incrimination on several questions and denied any knowledge of espionage. She was arrested on August 11.
Morton Sobell, an engineer and former classmate of Julius, was another member of the network. After Greenglass’s arrest, Sobell fled with his family to Mexico. Mexican authorities arrested him and turned him over to American officials. He was charged alongside the Rosenbergs.
The decision to arrest Ethel had a strategic purpose. Prosecutors believed that threatening her with prosecution and possibly a severe sentence might pressure Julius into cooperating. This strategy would eventually extend to seeking the death penalty against her.
After being taken into custody, both Rosenbergs proclaimed that they were innocent. This led to a meeting between 20 senior government officials who were trying to determine the best way to crack the Rosenberg case.
The chairman of the Atomic Energy Commission, Gordon Dean, decided that the best way to break the Rosenbergs was to have the death penalty loom over both of them.
This tactic was interesting, as the government had no evidence that Ethel was heavily involved in espionage. They hoped that by threatening them with the death penalty not just for Julius but also for Ethel, they would be able to get him to talk.
There is only one problem, Ethel didn’t seem to be heavily involved in the espionage Ring.
To make the suspicion on Ethel more convincing, they re-interviewed David Greenglass. In his original testimony, he had said that he handed off information on the atomic weapons to Julius on a New York street corner.
However, after his second interview, he claimed that he gave information on the atomic weapons to Julius at the Rosenbergs’ New York City apartment. Greenglass then directly implicates Ethel by stating that she had taken the notes on the atomic data he had provided and typed them up.
Interestingly, the charges against Greenglass’s own wife, Ruth, were dropped after he gave his second interview.
After Greenglass gave new testimony, Ethel testified before a grand jury about her involvement in the spy ring. During questioning, she invoked the Fifth Amendment.
By August 17, 1950, the grand jury created an indictment that alleged the Rosenbergs committed 11 counts of espionage. It should be noted that they were not charged with treason.
The Rosenbergs were tried on March 6, 1951, in the US District Court for the Southern District of New York. The prosecution based most of its case on the testimony of David Greenglass.
During the case, Greenglass served as the prosecution’s primary witness. On the stand, Greenglass testified that he gave Julius a sketch of part of an implosion-type atomic bomb.
With this testimony, the Rosenbergs were convicted of espionage on March 29, 1951. During sentencing, they received the death penalty under section 2 of the Espionage Act of 1917. Sobel, who was also tried with them, was sentenced to 30 years in prison.
David Greenglass received 15 years and ultimately served less than ten.
The US government did offer to spare the lives of the Rosenbergs if Julius admitted he was a spy and provided the names of other members of the ring. He declined to do so, stating that they were unwilling to be coerced into falsely claiming guilt.
After the Rosenbergs were sentenced to death, there were immediate questions on whether or not the punishment fit the crime. One main source of opposition was the National Committee to Secure Justice, a group formed to defend the Rosenbergs.
The organization began to publicly question the case proceedings. They pointed to evidence that the prosecution’s case and the conviction rested entirely on circumstantial evidence and on testimony that was likely perjured. There was no documented evidence that connected the Rosenbergs to espionage.
With these concerns, members of the clergy and leading scientists began to speak out, asking for the Rosenbergs to receive clemency. The movement eventually became so large that it received international attention.
The case got so much international attention that the pope at the time, Pope Pius XII, directly appealed to the newly inaugurated US president, Dwight Eisenhower, to spare the couple’s lives. Despite this appeal and public opinion, Eisenhower refused to pardon or commute the sentence of the Rosenbergs.
Despite the initial date of the execution being pushed back, both of the Rosenbergs were executed by electrocution on June 19, 1953. The Rosenbergs were the only American civilians to be executed for espionage during the Cold War.
In the decades following their execution, David Greenglass hyper-exaggerated his testimony about his sister. Other members of the spy ring confirmed that Julius was involved in the conspiracy but claimed that the information they passed on was of little value to the Soviet Union.
After the collapse of the Soviet Union in 1991, the Russian government briefly opened portions of Soviet intelligence archives to researchers. Former KGB officer Alexander Vassiliev was permitted to examine records and take extensive notes. The Soviet documents supported the conclusions that the British and American came to decades earlier in Operation Venona.
Julius had recruited several technically trained Americans and supplied information involving radar, proximity fuses, aviation, electronics, and other military technologies. His contribution was much broader than the atomic material that dominated his trial.
Morton Sobell maintained his innocence for decades. In 2008, at the age of 91, he finally admitted that he had passed military information to the Soviet Union and confirmed that Julius had participated in espionage.
Sobell described the material as relating primarily to radar and defensive weapons rather than atomic secrets. He said Ethel knew about Julius’s activities but was not personally involved in espionage. His admission provided additional independent confirmation that Julius’s network was real.
With everything that has come to light over the last 75 years, there is no doubt that Julius Rosenberg was guilty of espionage.
However, while there is ample evidence that Ethel was aware of her husband’s espionage, there is no evidence that she took an active part in it. Whatever crimes Ethel was guilty of, they were not capital crimes.
In 2024, a previously classified memorandum written in 1950 by Venona cryptanalyst Meredith Gardner received renewed attention. Gardner concluded that Ethel knew of Julius’s atomic espionage but did not engage in the work herself.
The memorandum appears to show that before Ethel’s trial, at least some American intelligence officials understood that available Soviet communications did not identify her as an active agent. Her sons argued that this proved the government knowingly prosecuted and executed someone it knew was not a spy.
The Soviet Union did benefit from Western atomic espionage, but the idea that the Rosenbergs alone “gave Russia the bomb” was an exaggeration. Fuchs and other agents supplied far more valuable scientific information, while Soviet scientists were capable of constructing a weapon themselves.
The lesson of the Rosenberg case is that real threats do not eliminate the need for fair procedures. Soviet espionage was real. Julius Rosenberg was guilty. But at the same time, Cold War fear helped produce a distorted prosecution, an unreliable case against Ethel Rosenberg, and a punishment far more severe than was imposed on spies who had actually delivered more valuable information.