Extraordinary story of secret ‘letter-writing group’ who used own URINE as invisible ink to reveal death camp horrors

A group of Girl Guides sent to the notorious Ravensbrück concentration camp for women, smuggled out letters written in ‘invisible ink’ – their own urine. Kalbar/TFN/ssaufseherin.fora.pl/ Im Gefolge der SS

In the darkest recesses of Hitler’s hellish concentration camp system, four young Polish Girl Guides were desperate for the world to know about the barbaric experiments that were being carried out on them.

Their one means of contact with the outside world was the monthly, heavily censored letter they were allowed to send to their families in Lublin.

The system they came up with was to write letters in invisible ink using their own urine. The idea was genius, but the story of how they let their families know that these formulaic, SS censored letters contained horrific details of German crimes and the secret communication network the girls maintained for one and half years is astonishing in its sheer audacity.

The group included four Girl Guides, Krystyna Czyż (pictured) the sisters Janina and Krystyna Iwańska and Wanda Wójtasik, who had been arrested for involvement with the Polish Underground. They would go on to create the secret letter writing group.Kalbar/TFN

Twenty seven of these letters are now held by the Museum of Martyrology in Lublin. Hidden for decades in the furniture of Krystyna Czyż, one of the letter-writers, they were found in 2010 by her daughter Maria, who later donated them to the museum.

Proof of the effectiveness of the invisible ink is that many of them can still be read easily today 77 years later.

Museum director Barbara Oratowska told TFN: “It is difficult to find any equivalent to the character, ingenuity and determination that these women showed in the worst of circumstances at such a young age.”

Desperate for the world to know about the barbaric experiments that were being carried out on them, the girl’s began writing the letters. Pictured: letter written in urine on the inside of a camp letter.Kalbar/TFN

On 21 September 1941, a group of 400 women from Lublin and Warsaw was taken to Ravensbrück, the notorious concentration camp for women near Berlin.

The group included four Girl Guides, Krystyna Czyż, the sisters Janina and Krystyna Iwańska and Wanda Wójtasik, who had been arrested for involvement with the Polish Underground. They would go on to create the secret letter writing group.

After two days packed tightly inside goods wagons, the transport reached the ‘Ravensbrück Model Camp’.

A secret letter written by Krystyna Czyż on the back of a camp envelope giving details of prisoners who were operated on, their camp numbers and the type of experiments carried out on them.Kalbar/TFN

They thought that here, surrounded by a forest and a lake, they would get some respite from the nightmare of detention in German-occupied Poland, where the young women had been exposed to ferocious violence during interrogations. They were wrong.

When the sonder transport arrived at Ravensbrück, next to their names there was the annotation: ‘return to Poland undesirable’. This was in effect a death sentence.

In the meantime, until their extermination the Germans set about exploiting the bodies of these young women in any way that could bring some utility to the Third Reich.

In the summer of 1942, SS doctors initiated a programme of inhumane medical experiments on a group of 86 women, which included 74 young Polish women and the group of four later letter-writers. They became known as the Rabbits of Ravensbrück.Fair use

In the summer of 1942, SS doctors initiated a programme of inhumane medical experiments on a group of 86 women, which included 74 young Polish women and the group of four later letter-writers. They became known as the Rabbits of Ravensbrück.

Their legs were sliced open with pieces of glass and wood, and bacteria were smeared into the wounds. The aim of the experiments was to test potential infection-fighting medications. But the ultimate aim was to exterminate all of these women.

Writing after the war, Krystyna Czyż explained: “We believed that the world needed to know about the disgraceful acts committed by the German doctors. We also knew that the information had to be full and precise. We were fully aware of the very real possibility that we would be exterminated as living proof.”

On 21 September 1941, a group of 400 women from Lublin and Warsaw was taken to Ravensbrück, the notorious concentration camp for women near Berlin.Bundesarchiv, Bild 183-1985-0417-15 / CC-BY-SA 3.0

She was correct in her prediction. Six of the group were shot when their wounds failed to heal and they became useless for the Germans.

To get information to the outside world, the group had to solve several problems. The first was how to write down the information.

“We decided that we would write everything in visible ink between the lines of the official letter,” Czyż, who was just 20 at the time, said, referring to the letter written in German that the prisoners were allowed to send home once a month.

Museum director Barbara Oratowska told TFN: “It is difficult to find any equivalent to the character, ingenuity and determination that these women showed in the worst of circumstances at such a young age.”Kalbar/TFN

The next problem was what to use as invisible ink. “Because we didn’t have available any other liquids that could be used as invisible ink we used our own urine. It turned out to be more practical than milk, or onion or lemon juice,” Czyż said.

The last problem was how to let their families know that the letters contained secret content. Czyż came up with an ingenious idea.

Back at home in Lublin, she had enjoyed reading stories for children with her brother by the popular pre-war author Kornel Makuszyński.

Twenty seven of the letters are now held by the Museum of Martyrology in Lublin, which during the war was used as an HQ by Hitler’s dreaded Gestapo.Kalbar/TFN

She mentioned this in the official part of the letter, referring in particular to a story in which a boy was caught by criminals and imprisoned. The kidnappers demanded that the boy write a letter to an adult friend saying that he had just gone on a trip for a few days and that he was okay.

In the letter that he wrote, the first letter of each line read from top to bottom revealed a secret message. Krystyna wrote how much she admired the boy’s cleverness and resourcefulness.

When the letter reached Lublin, Krystyna’s brother found these details odd, but he eventually understood her sister’s idea and deciphered the message.

The Girl Guide group also managed to smuggle out secret photos showing the horrific conditions at the camp.Kalbar/TFN

The message that Czyż actually wrote was ‘list moczem’ or letter in urine. However, her brother missed the last two letters, reading ‘list mocz’, which means soak the letter.

This meant that the content of the first letter became diluted in water and the content did not survive. However, the family were still able to read the message, which started: “We have decided to tell you the whole truth.”

The family eventually worked out what they had to do and started to iron each letter, the heat from which revealed the secret content.

Women at the camp were made to carry out forced labour whilst being supervised by guards.ssaufseherin.fora.pl/ SS propaganda album

In the first letter, Czyż described in dispassionate language the experiments that had taken place and provided a list of the women who had been experimented with their camp numbers.

She told her family to expect more letters and instructed them to how to confirm their receipt. Methods that the women invented included adding a blue thread in a parcel, which they were allowed to receive.

When the women received the secret signal that the first letter had been received they became completely absorbed in writing the letters.

One of the crematoria at the camp.Bundesarchiv, Bild 183-66475-0009 / CC-BY-SA 3.0

They improved their methods by using the inside of the envelopes filling all the empty space with secret messages. They also numbered each message so that their families would know if any were missing.

They expanded the group of women involved and eventually managed to send letters via the regular German postal service after women who left the camp each day in work groups made contact with Poles held at a nearby Oflag.

They divided longer reports into multiple sections and the families back in Lublin would meet to put together all the parts of a report.

One of the guards at Ravensbrück, Irma Grese  who was nicknamed the Hyena, was executed after the war.Public domain

The messages were not personal, and were more like intelligence reports. They avoided describing their personal suffering and occasionally added uplifting statements to bolster the moral of their families in Lublin.

Much of the content, though, concerned the experiments. A report from 24 March 1943 included the following details: “Further details of operations. Up to 16 January 1943, 70 people in total have been operated on. From this, 56 from the Lublin September transport, of which 36 were infection operations (without incision), 20 bone operations. […] In bone operations, each cut is reopened. Bones are operated on both legs or just one.”

A report from May 1943 gives details of executions carried out the Germans: “We are worried that they will want to get rid of the ones who have been operated on as living proof. Bear in mind that in the course of 20 months about a quarter of all the Polish women from political transports have been shot. On 30 April, five more were shot under the guise of being sent to Oświęcim.”

Another camp guard, Amelia Bortnowska, was given three years jail.PAP

Another report from December 1943 shows how the Germans exploited the women in every possible way.

“On December 11, the adjutant told block leaders of Polish blocks that there is a need for Polish women, only political prisoners, for the brothel in Mauthausen.”

“One of us told the commandant: ‘We are Polish political prisoners so please in the future do not propose such things’. She was immediately placed under arrest and our block had parcels confiscated for two weeks and 3 days without meals.”

The detailed descriptions that the group wrote in invisible ink of German crimes made their way to the Polish underground and eventually to the International Red Cross, the Vatican and the Polish government-in-exile in London.

One of the torture positions in which Krystyna Czyż was beaten by German guards.Kalbar/TFN

Warnings to the German authorities were broadcast on 3 May 1944 by a Polish radio station in England. In the broadcast, the Germans were told that the SS officers and doctors at the camp were responsible for the fate of the women, and they were warned that if any mass murders took place or experiments continued they and their families would be hunted down to the ends of the earth.

When information about the broadcast filtered back to camp it electrified the women, who saw that their efforts were bringing results.

The women maintained their secret correspondence with their families for a year and a half, from January 1943 to June 1944. It only stopped when the front line engulfed Lublin and correspondence became impossible.

After the war, the group stayed in contact.Kalbar/TFN

The four women managed to survive until the Red Army liberated the camp in April 1945. They all went on to live full lives after the war.

Wanda Wójtasik became a psychiatrist, Janina Iwańśka a journalist in France, Krystyna Iwańśka a doctor and Krystyna Czyż became an academic.

SS guards from Ravensbrück were put on trial after the war and the letters written by the group were used in evidence against them.

Eleven were sentenced to death.