Image copyright ALAMY

The USSR's role in the defeat of Nazi Germany World War Two 70 years ago is seen as the nation's most glorious moment. But there is another story - of mass rapes by Soviet soldiers of German women in the dying days of the war.

Some readers may find this story disturbing.

Dusk is falling in Treptower Park on the outskirts of Berlin and I am looking up at a statue dramatically outlined against a lilac sky. Twelve metres (40ft) high, it depicts a Soviet soldier grasping a sword in one hand and a small German girl in the other, and stamping on a broken swastika.

This is the final resting place for 5,000 of the 80,000 Soviet troops who fell in the Battle of Berlin between 16 April and 2 May 1945.

The colossal proportions of the monument reflect the scale of the sacrifice. At the top of a long flight of steps, you can peer into the base of the statue, which is lit up like a religious shrine. An inscription saying that the Soviet people saved European civilisation from fascism catches my eye.

But some call this memorial the Tomb of the Unknown Rapist.

Stalin's troops assaulted an uncounted number of women as they fought their way to the German capital, though this was rarely mentioned after the war in Germany - West or East - and is a taboo subject in Russia even today.

The Russian media regularly dismiss talk of the rapes as a Western myth, though one of many sources that tells the story of what happened is a diary kept by a young Soviet officer.

Image copyright Vitaly Gelfand

Vladimir Gelfand, a young Jewish lieutenant from central Ukraine, wrote with extraordinary frankness from 1941 through to the end of the war, despite the Soviet military's ban on diaries, which were seen as a security risk.

The so far unpublished manuscript paints a picture of disarray in the regular battalions - miserable rations, lice, routine anti-Semitism and theft, with men even stealing their comrades' boots.

In February 1945, Gelfand was stationed by the Oder River dam, preparing for the final push on Berlin, and he describes how his comrades surrounded and overpowered a battalion of women fighters.

"The captured German female cats declared they were avenging their dead husbands," he writes. "They must be destroyed without mercy. Our soldiers suggest stabbing them through their genitals but I would just execute them."

It gets worse.

One of the most revealing passages in Gelfand's diary is dated 25 April, once he had reached Berlin. Gelfand was whirling around on a bicycle by the River Spree, the first time he'd ever ridden one, when he came across a group of German women carrying suitcases and bundles.

Image copyright Vitaly Gelfand

In broken German, he asked them where they were going and why they had left their homes.

"With horror on their faces, they told me what had happened on the first night of the Red Army's arrival," he writes.

"'They poked here,' explained the beautiful German girl, lifting up her skirt, 'all night. They were old, some were covered in pimples and they all climbed on me and poked - no less than 20 men,' she burst into tears.

"'They raped my daughter in front of me,' her poor mother added, 'and they can still come back and rape her again.' This thought horrified everyone.

"'Stay here,' the girl suddenly threw herself at me, 'sleep with me! You can do whatever you want with me, but only you!'"

By this stage, German soldiers had been guilty of sexual violence and other horrors in the Soviet Union for almost four years, as Gelfand had become aware as he fought his way to Berlin.

"He went through so many villages in which the Nazis had killed everyone, even small children. And he saw evidence of rape," says his son, Vitaly.

Image caption Vitaly Gelfand discovered his father's diary after he died

The Wehrmacht was supposedly a well-ordered force of Aryans who would never contemplate sex with untermenschen.

But the ban was ignored, says Oleg Budnitsky, a historian at the Higher School of Economics in Moscow. Nazi commanders were in fact so concerned about venereal disease that they established a chain of military brothels throughout the occupied territories.

It's hard to find direct evidence of how the German soldiers treated Russian women - many victims never survived - but in the German-Russian Museum in Berlin, director Jorg Morre shows me a photograph taken in Crimea from a German soldier's personal wartime album. A woman's corpse is sprawled on the ground.

"It looks like she was killed by raping, or after the rape. Her skirt is pulled up and the hands are in front of the face," he says.

"It's a shocking photo. We had discussions in the museum, should we show the photos - this is war, this is sexual violence under German policy in the Soviet Union. We are showing war. Not talking about war but showing it."

As the Red Army advanced into what the Soviet press called "the lair of the fascist beast" posters encouraged troops to show their anger: "Soldier: You are now on German soil. The hour of revenge has struck!"

Image copyright Getty Images

In fact, the political department of the 19th Army, which fought its way into Germany along the Baltic Coast, declared that a true Soviet soldier would be so full of hatred that he would be repulsed by sex with Germans. But once again soldiers proved the ideologists wrong.

While researching his 2002 book, Berlin, The Downfall, historian Antony Beevor found documents about sexual violence in the state archive of the Russian Federation. They were sent by the NKVD, the secret police, to their boss, Lavrentiy Beria, in late 1944.

"These were passed on to Stalin," says Beevor. "You can actually see from the ticks whether they've been read or not - and they report on the mass rapes in East Prussia and the way that German women would try to kill their children, and kill themselves, to avoid such a fate."

Another wartime diary, this time kept by the fiancee of an absent German soldier, shows that some women adapted to the appalling circumstances, in order to survive.

Starting on 20 April 1945, 10 days before Hitler's suicide, the anonymous author is, like Vladimir Gelfand, brutally honest, with razor-sharp powers of observation and occasional flashes of gallows humour.

Describing herself as "a pale-faced blonde always dressed in the same winter coat", the diarist paints vivid pictures of her neighbours in the bomb shelter beneath her Berlin apartment block, including a "young man in grey trousers and horn-rimmed glasses who on closer inspection turns out to be a young woman" and three elderly sisters, "all dressmakers, huddled together like a big black pudding".

Image copyright German-Russian Museum Image caption Soviet soldiers distribute food in Berlin, in May 1945 (photograph: Timofey Melnik)

As they await the arrival of the Red Army, they joke "better a Russky on top than a Yank overhead" - rape is preferable to being pulverised by bombs. But when the soldiers reach their basement and try to haul women out, they beg the diarist to use her Russian language skills and complain to the Soviet command.

Braving the chaos on the rubble strewn streets, she manages to find a senior officer. He shrugs his shoulders. Despite Stalin's decree banning violence against civilians, he says, "It happens anyway."

The officer returns to the cellar with her and reprimands the soldiers, but one is seething with fury.

"'What do you mean? What did the Germans do to our women!' He is screaming: 'They took my sister and…' The officer calms the man down and gets them outside."

But when the diarist steps back into the corridor to check they have gone, the men have been lying in wait and grab her. She is brutally raped and nearly strangled. The terrified neighbours, or "cave dwellers" as she calls them, had slammed the basement door shut.

"Finally the two iron levers open. Everyone stares at me," she writes. "My stockings are down to my shoes, I'm still holding on to what's left of my suspender belt. I start yelling 'You pigs! Here they rape me twice in a row and you leave me lying like a piece of dirt!'"

Eventually the diarist realises that she needs to find one "wolf" to stave off gang rape by the "male beasts". The relationship between aggressor and victim becomes less violent, more transactional - and more ambiguous. She shares her bed with a senior officer from Leningrad with whom she discusses literature and the meaning of life.

"By no means could it be said that the major is raping me," she writes. "Am I doing it for bacon, butter, sugar, candles, canned meat? To some extent I'm sure I am. In addition, I like the major and the less he wants from me as a man, the more I like him as a person."

Image copyright Getty Images Image caption US troops watch a Russian soldier with a female friend in Berlin

Many of the diarist's neighbours made similar deals with the conquerors in the ruins of Berlin.

When the diary was published in German in 1959 under the title A Woman in Berlin, the author's frank account of the choices she made to survive was attacked for "besmirching the honour" of German women. Not surprisingly, she refused to allow the book to be republished until after her death.

Seventy years after the end of the war, new research on sexual violence committed by all the Allied forces - American, British and French as well as Soviet - is still emerging. But for years the subject slid under the official radar. Few reported it and even fewer would listen.

Besides the social stigma, in East Germany it was sacrilegious to criticise Soviet heroes who had defeated fascism while across the Wall in the West, the guilt for Nazi crimes made German suffering unmentionable.

But in 2008, there was a film adaptation of the Berlin Woman's diary called Anonyma, starring the well-known German actress Nina Hoss. The film had a cathartic effect in Germany and encouraged many women to come forward, including Ingeborg Bullert.

Image copyright Dorothy Feaver Image caption Ingeborg: "My mother liked to boast that her daughter hadn't been touched"

Ingeborg, aged 90, now lives in Hamburg in a flat filled with photos of cats and books about the theatre. She was 20 in 1945, dreamed of becoming an actress and lived with her mother in an upmarket street in Berlin's Charlottenberg district.

When the Soviet assault on the city began, like the woman diarist, she took refuge in the cellar of her building.

"Suddenly there were tanks in our street and everywhere the bodies of Russian and German soldiers", she recalls. "I remember the dreadful whining sound made by those Russian bombs - we called them Stalinorgels (Stalin organs)."

During a lull in the air raid, Ingeborg left the cellar and ran upstairs to look for a piece of string to use as a wick for a lamp. "Suddenly there were two Russians pointing their pistols at me," she says. "One of them forced me to expose myself and raped me, and then they changed places and the other one raped me as well. I thought I would die, that they would kill me."

Ingeborg didn't talk about her ordeal at the time, or for decades afterwards - she said it was too difficult. "My mother liked to boast that her daughter hadn't been touched," she says.

Image copyright Ingeborg Bullert Image caption Ingeborg: "I thought I was going to die"

But the rapes had affected women in households across Berlin. Ingeborg recalls that women between the ages of 15 and 55 were ordered to get tested for sexually transmitted diseases. "You needed the medical certificate to get the food stamps and I remember that all the doctors doing these certificates, had waiting rooms full of women."

What was the scale of the rapes? The most often quoted number is a staggering 100,000 women in Berlin and two million on German territory. That figure - hotly debated - was extrapolated from scant surviving medical records.

In a former munitions factory which now houses the State Archive, Martin Luchterhand shows me an armful of blue cardboard folders. These contain abortion records dated July to October 1945 from Neukolln, just one of Berlin's 24 districts - it's a small miracle that they survived intact.

Abortions were illegal in Germany according to Article 218 of the penal code, but Luchterhand says "there was a small window for those women because of that special situation of the mass rapes in 1945".

Image copyright Dorothy Feaver

Image copyright Dorothy Feaver

Altogether 995 pleas for abortion were approved by this one district office in Berlin office between June 1945 to 1946. The files contain over 1,000 fragile scraps of paper of different colours and sizes. In childish round handwriting, one girl testifies that she was assaulted in the living room of her home in front of her parents.

We will probably never know the true scale of the rapes. Soviet military tribunals and other sources remain classified. The Russian parliament recently passed a law which says that anyone who denigrates Russia's record in World War Two could face fines and up to five years in prison.

Vera Dubina, a young historian at the University of Humanities in Moscow, says she knew nothing of the rapes until a scholarship took her to Berlin. She later wrote a paper on the subject but struggled to get it published.

"The Russian media reacted very aggressively," she says. "People only want to hear about our glorious victory in the Great Patriotic War and now it is getting harder to do proper research."

Image copyright Getty Images

It's the fate of history to be rewritten to suit the agenda of the present. That's why first-hand accounts are so valuable - from those who brave the subject now, in their old age, and from those younger voices who put pencil to paper on the spot.

Vitaly Gelfand, son of the Red Army diarist Vladimir Gelfand, doesn't deny that many Soviet soldiers showed great bravery and sacrifice in World War Two - but that's not the whole story, he says.

Recently Vitaly did an interview on Russian radio, which triggered some anti-Semitic trolling on social media, saying the diary's a fake and he should clear off to Israel (he has in fact lived in Berlin for the last 20 years). Yet he is hoping the diary will be published in Russia later this year. Parts of it have been translated into German and Swedish.

"If people don't want to know the truth, they're just deluding themselves", he says. "The entire world understands it, Russia understands it and the people behind those new laws about defaming the past, even they understand it. We can't move forward until we look back."

The Battle for Berlin (April - May 1945)

Image copyright Getty Images Image caption Red Army soldier raises the Soviet flag over the Reichstag in Berlin

After the Red Army captured Vienna, Joseph Stalin ordered his forces on to Berlin, determined to take the city before US forces

Two and a half million Red Army troops, 6,000 tanks and more than 40,000 artillery pieces were deployed, supported by thousands of aircraft

After heavy fighting and substantial losses, by 21 April, Red Army soldiers had entered the outlying suburbs of Berlin

In a staff conference on 22 April Adolf Hitler came close to admitting defeat but instead resolved to fight on, directing troops from his underground bunker

As Soviet forces took the city, it is estimated that close to 100,000 women were raped by Red Army soldiers

On 30 April Hitler killed himself and by 2 May the Reichstag had fallen

World War Two: History's most savage and devastating war

The Rape of Berlin is on BBC World Service on Saturday 2 May at 18.06 BST and Sunday 3 May at 11.06 BST, or listen on iPlayer

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