The Brilliant Code Used by Concentration Camp Inmates to Tell the World About Nazi Experiments

18 May

‘As a sign that you have read this, send me a blue thread in a parcel’: The heroic tale of young Ravensbrück inmates whose coded messages to their families were no less than genius.

The 27 letters were hidden for decades. Stuffed into furniture in the home of Krystyna Czyz, they were found by her daughter only in 2010. All were written by Czyz and sent to her parents from the Ravensbrück concentration camp in Germany. All contained secret, coded messages that were added to the text by way of a simple but clever method: writing with urine. With courage and daring, a small group of inmates managed to send out reports about the crimes being perpetrated in the camp, particularly the medical experiments carried out on them.

Krystyna Czyz was only 15 when she decided for the first time to resist the Nazi occupation regime, immediately after the Germans invaded Lublin, her hometown in September 1939. Her parents joined a clandestine cell that provided classes for children whose schools had been shut down, while their daughter served as a communications officer and lookout in the Polish underground. Czyz was arrested in 1941, and after half a year of Gestapo interrogations and torture she was deported, along with other adolescents and women from the underground, to the Ravensbrück concentration camp, where she was forced to wear the inverted red-triangle patch denoting her status as a political prisoner.

Krystyna Czyz. “Under the Clock” Museum of Martyrdom

Tens of thousands of women – Germans, Jews, members of the resistance, Gypsies – were incarcerated in the camp, situated north of Berlin. Most of them were ultimately murdered. In the summer of 1942, SS physicians began to conduct medical experiments on them under the direction of Karl Gebhardt, who had the distinction of being the personal physician of SS head Heinrich Himmler. The victims included at least 74 young Polish women, most of them members of the underground. Their legs were gashed with pieces of glass and wood, and bacteria were introduced into the wounds. The ostensible aim of the experiments was to test potential infection-fighting medications. The Germans termed the victims “rabbits.” Czyz and her friends Wanda Wijtasik, Janina Iwaska and Janina’s little sister Krystyna were among them. The physical damage inflicted on them made even the thought of escape pointless.

In January 1943, after months of brutal experiments, Czyz, now 20, and her friends decided to rebel – by reporting secretly about the experiments to the Polish underground. By this means, they thought, the reports would be conveyed to the Polish government in exile, the International Red Cross and foreign governments, and the horrific crimes being committed by the doctors in the camp would be revealed to the world.

The question was how to get the information out of the camp. Their only form of communication with the outside world was the one letter each inmate was permitted to write to her family once a month. The letter had to be written in German, its content limited to a report about their supposedly good situation, and it was subject to SS censorship. Anyone who deviated from the restrictions risked death. One member of the group suggested bribing the camp’s female guards or administrative personnel to smuggle the letters out, but they knew that if they were informed upon, they would be executed. A cleverer solution was needed.

The very next day four young inmates – Krystyna, Wanda, Janina and her sister – wrote letters to their families. Ostensibly, they were as mundane as the earlier missives. In an interview with her that was published in 2015 in a book about the camp’s history, Czyz related that when her family received the letter, her father read it aloud and they all scrutinized the text for hints about her health, but the usual blandness seemed to prevail. Nevertheless, something about the letter struck Krystyna’s brother as different. His sister mentioned in it their admiration for the children’s book “Satan from the Seventh Grade,” recalling how amazed they had been at the protagonist’s cleverness and resourcefulness. He found the mention of the book odd. Why was his sister suddenly referring to a book they had adored as children? But then he remembered the novel’s plot and understood the hint.

The book, by the Polish writer Kornel Makuszyski, tells the story of a seventh grader who is known for his acute intelligence and his detective skills. While investigating a mystery he is caught by criminals and imprisoned in a cellar. To ensure that his disappearance does not arouse suspicion, they demand that he write a letter to an adult friend of his, a professor, saying that he’s gone on a trip for a few days. The boy writes the following letter:

A letter with urine encryption from the women’s concentration camp in Ravensbrueck, written by one of the prisoners, is presented at the Martyr Museum in Lublin, Poland, February 17, 2017. STRINGER/REUTERS

“Greetings to you, Mr. Professor! I may be a little insane, because I have gone completely on my own to an unfamiliar area, but luck plays into the hands not only of sane people but also insane ones like myself, and I am only sorry, Mr. Professor, that you are not here with me. It didn’t take long before I found a delightful girlfriend, so I don’t know when I will be back. I am enjoying the trip very much. Long live summer vacation! The area here is very pretty, and I write this without exaggeration and from sincere observation, but even so, Ejgola is much prettier. Regards to Wanda, and I miss Mrs. Teresa and all the occupants of the house. Yours, Adam.”

The recipient finds the letter suspicious. To begin with it, the way it was written was confusing, with some of the lines being short and others long, with no obvious logic. Some sentences broke abruptly midway through, only to continue on the next line, and there were also mistakes in several of the names mentioned in the letter. The recipient inferred that the deliberate mistakes were intended to attract his attention and to signal the presence of a secret message embedded in the text. It emerged that the letter contained an acrostic, spelling out the warning: “Safeguard the house.”

Krystyna’s brother thus inferred that she too must be sending a secret message. Even though the letter was blurry, the family was able to work out an acrostic. The concealed message was “list moczem,” meaning “letter in urine,” in Polish. When it comes in contact with paper, urine loses its color quickly and becomes invisible on the page. However, if the paper is heated, the writing reappears. Czyz’s mother applied a hot iron and the secret message was revealed.

“We have decided to tell you the whole truth,” Krystyna wrote in the margins of the letter using a thin stick dipped in her urine. She elaborated on the medical experiments to which she and her friends had been subjected, and signed off by noting that the family should expect similar letters in the future. Czyz was sufficiently resourceful to ask her parents to acknowledge – in code – in their next letter to her that the secret message had been received. She, for her part, read the response from her family carefully, to find the code word that confirmed that her message had been deciphered.

The four inmates sent increasing numbers of coded letters. They improved their methods, filling every empty space in the letter and even the envelope with the clandestine messages. To transmit longer messages, they divided the text and each of them sent part of it to her family; the families then met secretly to piece together the full text. The messages in the letters described the atrocities perpetrated in the camp, including the experiments conducted by the German doctors. They also reported the death of several young women in the wake of the experiments, and noted the physical and mental damage suffered by those who survived. The letter writers stuck scrupulously to the facts and refrained from complaining about the situation or about the conditions in the camp. They provided first-hand testimony about the crimes being perpetrated in Ravensbrück, in the hope that revelation of the information would somehow help to bring about an end to the Nazis’ deeds.

Female prisoners at Ravensbrück, marked for deportation to death camps. UtCon Collection / Alamy

“Up to January 16, 1943, 70 persons were operated on altogether,” Czyz wrote in a secret message in March 1943. “Out of this number, 56 were from the Lublin September transport, 36 of these operations began with infection (3 without incision) and 20 bone operations. In bone operations, each incision is opened again. No more new operations since Jan 15.”

She went on to list the names of the victims, their serial number in the camp and the type of operation they underwent. “Infection operations August 1st 1942: Wojtasik Wanda 7709, Gna Maria 7883, Zielonka Maria 7771…” She added the names of the doctors who carried out the experiments (source: “Ravensbrück: Inside Hitler’s Concentration Camp for Women,” by Sarah Helm).

“As a sign that you have read this letter, send me a blue thread in a parcel …,” she wrote to her parents. “You can send a note hidden in the double bottom of a tin. Write at least once, describe the political situation. I am waiting for that! Message continued in letters from Wanda and Janina.”

At the same time, the young women made plans to escape from the camp. In May 1943 Janina Iwaska’s father received a letter in German from his daughter: “Dear Bolust! I received packages from you on 23/IX [Sept. 23] and 5/X [Oct. 5]. We thank you very much for this. I am writing you a very short letter today, because I don’t have much time. But Ninka is writing a long letter. She is released from work for a few days due to illness. In her letter you will discover exactly how we spent Easter. There is nothing new here, spring is marvelous. Thanks to everyone for sending regards. I kiss you strongly.”

The real message appeared on the envelope holding the letters, and was decoded by Janina’s father: “Five female Polish political inmates have escaped. We are preparing a new escape. Send in a parcel: a compass, an accurate map of Germany, two false identification documents with photographs that are not especially characteristic. As much Reichsmarks as possible and some jewelry (gold!). Send to: Krzysio Starszy in the Generalgouvernement, possibly through the organization. Comfortable shoes, 2 sponges. The mission [must be carried out by] June 20th, please hurry… Address the parcel to me. The map, identification documents and money, you should send in a strong, double-bottomed box.

A letter Janina Iwaska wrote to her father.

“You have to do it very skillfully, carefully and invisible … underneath a jar of jam, a secret message tucked in a tube of toothpaste. At the bottom a rusks box. Sender: Agnieszka Kopertowska, Krakowskie Przedmiescie 26.4. Destroy the letter, in case anything happens, you know nothing.” (Source:; Polish Research Institute, Lund University, Sweden).

Whether the plan to escape was implemented fully is not clear, but all four women survived. After the war Czyz went on to pursue an academic career; Wanda became a psychiatrist; Janina was a journalist in Paris; and her younger sister became a doctor.

For their part, Czyz’s parents forwarded the detailed reports to the leaders of the underground in Lublin. From there they were sent on to Warsaw, then to the Polish government in exile based in London, which conveyed them to the headquarters of the International Red Cross in Geneva and to the Vatican. The government in exile called for a halt to the crimes being committed in the camp. The IRC replied that the subject was being examined but that the German authorities did not permit visits to the camp.

Despite that, the contents of the letters were made known to the world. At 7:10 P.M. on May 3, 1944 – nearly a year and a half after the first secret message was transmitted – a radio station in England belonging to the Polish underground broadcast an item based on the secret messages in the letters. The broadcast was meant for the world, but primarily for German intelligence who would be listening in. “In the concentration camp for women in Ravensbrück,” the announcer said, “the Germans are committing new crimes. The women in this camp are being submitted to vivisection experiments and are being operated on like rabbits. The [occupation] authorities have made lists of all women who had to submit to such operations. It is feared that these records are being kept for the purpose of murdering these women so as to obliterate all traces of their crimes… At present there are close to 3,000 Polish women in the Ravensbrück camp.”

The broadcast continued with a warning to those in charge in the camp: “For the fate of the women in the concentration camp of Ravensbrück all Germans are responsible: SS officers and doctors of the administration of the camp. The prime responsibility therefore falls on the commandant of the camp… his adjutant… and the chief woman guard. All these we are warning solemnly that if any mass murders are committed, or if the vivisection experiments continue, they will be held responsible – they and their families. We have established their identity and we are finding out particulars about their families. May they remember that their days are numbered. We shall find them even if they are to hide under the earth. None of the hired assassins of Ravensbrück will escape justice.” (Source: Sarah Helm)

Defendant Karl Brandt is sentenced to death at the conclusion of the Doctors’ Trial, in Nuremberg, August 1947. United States Government

Czyz related in an interview that news of the radio broadcast reached the inmates and stirred great excitement. After months of risking their lives on a daily basis, the four young women discovered that their reports were reaching destinations far beyond the gates of the camp.

After the war Czyz studied geography and became a research fellow at Lublin’s Maria Curie-Skłodowska University. She passed away in 2011.

Death by hanging

In 1945, as the Nazis’ defeat loomed, the SS began the evacuation of Ravensbrück; most of the prisoners still alive were sent on a death march in Germany. On April 30, the Red Army liberated those who remained. The four letter-writers survived and went on to have families. The female SS guards and warders were captured by the Allies and tried in Hamburg in the 1946-1948 Ravensbrück trials. The secret messages transmitted by the victims of the experiments were entered in evidence against them. Eleven of them were sentenced to death for war crimes and crimes against humanity. Karl Gebhardt, who supervised the experiments in the camp, was sentenced to death in the Doctors Trial held in Nuremberg in 1946-47. He was hanged on June 2, 1948.

This article is based on a chapter from Dr. David Gil’s forthcoming Hebrew-language book “The Art of Hiding.”

As taken from,

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Posted by on May 18, 2019 in Uncategorized


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