Ravensbrück: Life and Death in Hitler’s Concentration Camp for Women. By Sarah Helm. Nan A. Talese; 743 pages; $37.50. Little, Brown; £25.

AS SHE searched for survivors of Ravensbrück, a concentration camp 50 miles (80km) north of Berlin, Sarah Helm came home one day to find a French voice on her answering machine. The message was from Louise Le Porz, a doctor from Bordeaux, who asked her to visit. There was much to talk about, she said to Ms Helm, a British journalist. “But you’d better hurry. I’m 93 years old.”

A sense of urgency infuses this history, which comes just in time to gather the testimony of the camp’s survivors. Ravensbrück has had far less attention than Auschwitz and other Nazi death camps. What happened there was covered up. The files were burned as the Allies drew near in 1945. Later, Soviet tanks bulldozed the buildings. The camp’s history soon became divided, like Europe. East Germany had its own, selective version, stressing the heroism of the communists among the inmates; the West, without ready access to the site and with evidence from war-crimes trials on the camp classified as “secret”, largely ignored it. In the late 1960s some historians even started to question the existence of the gas chambers there.

Yet Ravensbrück deserves to be remembered. It was Hitler’s only concentration camp specifically for women. Towards the end of the war, as other camps emptied, it became the engine of the Nazi killing machine on the orders of Heinrich Himmler, without even the pretence of an ideological reason, however perverted. This was killing for the sake of killing.

About 130,000 women passed through the camp. Ms Helm estimates that 40,000-50,000 died. Jews made up only about 10% of the prisoners. The rest were communists, Jehovah’s Witnesses, gypsies, prostitutes and women simply swept up by the events of the war in Europe. By 1944 the camp held women of 21 nationalities; besides Germans, the largest groups were Poles, Russians and French.

Many of the prisoners were desperate for the world to know about the horrors taking place there. “We need to make a film to show everyone that this really happened,” said an Austrian prisoner, Käthe Leichter, in early 1942. “And you’ll see, even when it is all over no one will believe us.”

Women taken away on the first death transports hid notes for their friends in the camp to find when their clothes were returned there, telling them where they were being taken. Using urine as invisible ink in otherwise censored letters, Krysia Czyz and other Polish prisoners told their families about the obscene medical experiments being carried out on them; in 2010 Czyz’s daughter discovered 27 of these secret letters hidden in her grandmother’s old rolling pin and a chopping board. After the war Soviet censors stopped Antonina Nikiforova, a Russian doctor brought to Ravensbrück in 1944, from publishing her account, but she refused to give up and asked fellow Red Army survivors to write to her with their memories; their letters recently reached the camp archive.

Others were less keen to trumpet the truth. The Red Cross in Geneva was told in 1943 that Polish women in Ravensbrück were being injected with gangrene to test new drugs and having healthy limbs amputated as part of an experiment about transplants. Yet it stayed silent, preferring, it said, to “work behind the scenes”. Ms Helm also criticises the evasive and “mealy-mouthed” response to questions put to Siemens, which operated a factory at the camp producing electrical parts for fighter planes.

Yet the details are now pouring out, in such abundance that they seem hard to control at times. Survivors want to talk, documents from war-crimes trials have been released, archives have been opened after the collapse of Soviet rule. All this enables Ms Helm to piece together the camp’s “biography” with meticulous, unblinking thoroughness. Her book comes not a moment too soon.