A Danish ambulance driver huddled over a Copenhagen phone book, circling Jewish names. As soon as he’d heard the news—that all of Denmark’s Jews would be deported by the Nazis the next day—he knew he had to warn them.

The man was just one of hundreds, perhaps thousands, of normal Danes who sprang into action in late September 1943. Their objective was simple: Help their Jewish friends and neighbors. Soon, Jewish people were sneaking out of Copenhagen and other towns, headed toward Danish shores and into the crowded holds of tiny fishing boats.

Denmark was about to pull off a spectacular feat—the rescue of the vast majority of its Jewish population. Within hours of learning that the Nazis intended to wipe out Denmark’s Jews, nearly all Danish Jews had gone into hiding. Within days, most of them had escaped Denmark to neutral Sweden. The miraculous-seeming rescue of over 90 percent of Danish Jews happened thanks to ordinary Danes, most of whom refused to accept credit for the lives they saved.

In April 1940, German forces invaded Denmark. They didn’t meet with much resistance. Rather than suffer an inevitable defeat by fighting back, the Danish government negotiated to insulate Denmark from the occupation. In return, the Nazis agreed to be lenient with the country, respecting its rule and neutrality. However by 1943, tensions had reached a breaking point.

Workers had begun to sabotage the war effort and the Danish resistance had ramped up efforts to fight the Nazis. In response, the Nazis told the Danish government to institute a harsh curfew, forbid public assemblies, and punish saboteurs with death. The Danish government refused, so the Nazis dissolved the government and established martial law.

The Nazis had always been a forbidding presence in Denmark, but now they made their presence known. Danish Jews were among their first targets. The Holocaust was already in full swing across occupied Europe, and without the protection of the Danish government, which had done its best to shield Jews from the Nazis, Denmark’s Jewish population was in danger.

Then, in late September 1943, the Nazis got word from Berlin that it was time to rid Denmark of its Jews. As was typical for the Nazis, they planned the raid to coincide with a significant Jewish holiday—in this case, Rosh Hashanah, the Jewish New Year. Marcus Melchior, a rabbi, got word of the coming pogrom, and in Copenhagen’s main synagogue, he interrupted services.

“We have no time now to continue prayers, said Melchior. “We have news that this coming Friday night, the night between the first and second of October, the Gestapo will come and arrest all Danish Jews.” Melchior told the congregation that the Nazis had the names and addresses of every Jew in Denmark, and urged them to flee or hide.

As Denmark’s Jewish population sprang into panicked action, so did its Gentiles. Hundreds of people spontaneously began to tell Jews about the upcoming action and help them go into hiding. It was, in the words of historian Leni Yahil, “a living wall raised by the Danish people in the course of one night.”

The Danish people didn’t have pre-existing plans designed to help the Jews. But nearby Sweden offered an obvious haven to those who were about to be deported. Neutral and still unoccupied by the Nazis, the country was a fierce ally. It was also close—in some cases, just over three miles away from the Danish coast. If the Jews could make it across, they could apply for asylum there.

Danish culture has been seafaring since Viking times, so there were plenty of fishing boats and other vessels to spirit Jews toward Sweden. But Danish fishermen feared losing their livelihoods and being punished by the Nazis if they were caught. Instead, the resistance groups that swiftly formed to help the Jews managed to negotiate standard fees for Jewish passengers, then recruit volunteers to raise the money for passage. The average price of passage to Sweden cost up to a third of a worker’s annual salary.

“Among the fishermen there were some who exploited the situation, just as it is equally clear that there were more who acted without regard to personal gain,” writes historian Bo Lidegaard.

Passage was a terrifying ordeal. Jews congregated in fishing towns, then hid on small boats, usually 10 to 15 at a time. They gave their children sleeping pills and sedatives to keep them from crying, and struggled to maintain control during the hour-long crossing. Some boats, like the Gerda III, were boarded by Gestapo patrols. Others sailed with gas obtained by careful rationing in towns like Elsinore, where the “Elsinore Sewing Club,” a resistance unit, helped a few hundred Jews make the crossing.

The rescues weren’t always successful. In Gilleleje, a small fishing town, hundreds of refugees were cared for by locals. But when the Gestapo arrived, a collaborator betrayed a group of Jews hiding in the town church’s attic. Eighty Jews were arrested. Others never got word of the upcoming deportations or were too old or incapacitated to seek help. About 500 Danish Jews were deported to the Theresienstadt ghetto.

Still, it was the most successful action of its kind during the Holocaust. Some 7,200 Danish Jews were ferried to Sweden, and of the 500 who were deported to the Theresienstadt ghetto, only 51 did not survive the Holocaust.

The rescue seemed miraculous, but some factors did lead to its success. Werner Best, the German who had been placed in charge of Denmark, apparently tipped off some Jews to the upcoming action and subtly undermined the Nazis’ attempts to stop the Danes from helping Danish Jews. And Denmark was one of the only places in Europe that had successfully integrated its Jewish population. Though there was anti-Semitism in Denmark before and after the Holocaust, the Nazis’ war on Jews was largely viewed as a war against Denmark itself.

After the war, most Danes refused to take credit for their resistance work, which many had conducted under false names. Ordinary people who never considered themselves part of the Danish Resistance passed along messages, gathered food, gave hiding places or guarded the possessions of those who left until they returned home from the war.

The rescue of Denmark’s Jews was an extraordinary feat—one that wouldn’t have been possible without ordinary people.