When the men of the 42nd “Rainbow” Division rolled into the Bavarian town of Dachau at the tail end of World War II, they expected to find an abandoned training facility for Adolf Hitler’s elite SS forces, or maybe a POW camp.

What they discovered instead would be seared into their memories for as long as they lived—piles of emaciated corpses, dozens of train cars filled with badly decomposed human remains, and perhaps most difficult to process, the thousands of “walking skeletons” who had managed to survive the horrors of Dachau, the Nazi’s first and longest-operating concentration camp.

“Almost none of the soldiers, from generals down to privates, had any concept of what a concentration camp really was, the kind of condition people would be in when they got there, and the level of slavery and oppression and atrocities that the Nazis had perpetrated,” says John McManus, a professor of U.S. military history at the Missouri University of Science and Technology, and author of Hell Before Their Very Eyes: US Soldiers Liberate Concentration Camps in Germany, April 1945.

“It was stunning.”

The liberation of Dachau by American troops on April 29, 1945, wasn’t the first such deliverance by Allied troops. The Soviets had found and freed what remained of Auschwitz and other death camps months earlier. But the wrenching images and first-hand testimonies recorded by Dachau’s shocked liberators brought the horrors of the Holocaust home to America.

When Dachau opened in 1933, the notorious Nazi war criminal Heinrich Himmler christened it “the first concentration camp for political prisoners.” And that’s what Dachau was in its early years, a forced labor detention camp for those judged as “enemies” of the National Socialist (Nazi) party: trade unionists, communists, and Democratic Socialists at first, but eventually Roma (Gypsies), homosexuals, Jehovah’s Witnesses and of course, Jews.

The cruelly efficient operation of Dachau was largely the brainchild of SS officer Theodor Eike, who instituted a “doctrine of dehumanization” based on slave labor, corporal punishment, flogging, withholding food and summary executions of anyone who tried to escape. The Dachau prisoners labored under brutal conditions tearing down a massive WWI-era munitions factory and then constructing the barracks and offices that would serve as the chief training ground for the SS.

The prisoners even built their own “protective custody camp,” the euphemistically named concentration camp within the sprawling Dachau complex, composed of 32 squalid barracks surrounded by an electrified barbed-wire fence, a ditch and seven guard towers. Prisoners were subjected to medical experiments, including injections of malaria and tuberculosis, and the untold thousands that died from hard labor or torture were routinely burned in the on-site crematorium.

Forged into the iron gate separating the concentration camp from the rest of Dachau were the taunting words, Arbeit Macht Frei (“Work sets you free”). Dachau was such a success for the Nazis that Eike was promoted to inspector general of all German concentration camps, for which Dachau became the model.

After the events of Kristallnacht (“night of broken glass”), in which Jewish synagogues, businesses and homes were destroyed by Nazi mobs across Germany, a greater and greater number of Jews were held at Dachau. On the eve of the American liberation of Dachau, there were 67,665 registered prisoners at the concentration camp and roughly a third of them were Jewish.

For the unwitting U.S. infantrymen who marched into Dachau in late April 1945, the first clue that something was terribly wrong was the smell. Some soldiers thought they were downwind from a chemical factory, while others compared the acrid odor to the sickening smell of feathers being burned off a plucked chicken. None of their prior combat experiences prepared them for what lay ahead.

Weeks earlier, Nazi commanders at Buchenwald, another notorious German concentration camp, packed at least 3,000 prisoners into 40 train cars in order to hide them from the approaching Allied armies. The train was supposed to arrive in Dachau a few days later, but the tortuous odyssey ended up lasting three weeks. All but a quarter of the train’s 3,000 passengers died from starvation, dehydration, asphyxiation and disease. The survivors were herded into the concentration camp while thousands of fallen corpses were left to rot on the railway cars.

“If you’re a U.S. soldier arriving at Dachau, you’d almost certainly see the ‘death train’ first,” says McManus.

The abhorrent sights and smells of the death train left many American soldiers physically sick and emotionally shell-shocked, but it was only a taste of the horrors awaiting them inside the actual camp. In the weeks leading up to the liberation, the Nazis had shipped in prisoners from across Germany and as far away as Auschwitz. Like the survivors of the Buchenwald death train, these new arrivals were starving and riddled with diseases like typhus.

The Dachau prison guards packed the new arrivals into the already overcrowded barracks, cramming up to 1,600 men into buildings designed for 250. Starvation and disease tore through the camp, claiming the lives of thousands of prisoners just days before the liberation. The Nazis tried to cremate as many of these bodies as they could before abandoning Dachau, but there were too many. Another 7,000 Dachau prisoners, mostly Jews, were sent on a death march to Tegernsee in the south, during which stragglers were shot and thousands of others died from exhaustion.

When the American GIs entered the concentration camp, they found piles of naked corpses, their skin stretched tight across impossibly malnourished bodies. In interview after interview, the soldiers described the dead bodies being “stacked like cordwood,” a metaphor that unintentionally robbed the fallen prisoners of their remaining humanity. But for the soldiers to think of those bodies as fully human at that moment would have been too much to bear.

“Everywhere you turn is just this horror of bodies, and people near death or in a state of complete decrepitude that you can’t even process it,” says McManus.

When the American soldiers of the 45th “Thunderbird” Division stumbled upon the death train, it was like lighting a fuse that couldn’t be snuffed out. The men of the 45th had been in combat for 500 days and thought they had witnessed every grisly atrocity that war could throw at them. But then there was this train filled with innocent bodies, their eyes and mouths open as if crying out for mercy. Many of the American soldiers broke down in sobs. Others seethed with red-hot rage.

When four German officers emerged from the woods holding up a white handkerchief, Lt. William Walsh marched them into one of the box cars littered with corpses and shot them with his pistol. When the mortally wounded Germans cried out in agony, other American GIs finished the job.

Inside Dachau, it only got worse. An estimated 50 to 125 SS officers and assorted German military, including hospital personnel, were rounded up in a coal yard. Walsh called for a machine gun, rifles and a Tommy gunner. When the soldiers began loading a belt of bullets into the machine gun, the German prisoners stood up and began to move toward their American captors. That’s when Walsh allegedly took out his pistol and yelled, “Let them have it!”

After a 30-second flurry of gunfire, at least 17 German prisoners lay dead in the Dachau coal yard.

“I will tell you, as someone who has studied this in a great deal of depth, that this is pretty much the only time that American soldiers do this among many, many liberations in many places,” says McManus. “The separating factor is leadership because you have a company commander who is so deeply upset at what he’s seen that he just loses it. And when a leader loses it, soldiers are going to lose it, too.”

Chief among the many traumatic experiences that awaited the liberators at Dachau was encountering the surviving prisoners who numbered around 32,000. “Walking skeletons” was the only way to describe their condition of extreme malnourishment and illness. Ridden with typhus and lice, the overwhelmed prisoners grabbed at their liberators’ uniforms in disbelief that their tortuous ordeal was finally over.

Unprepared and ignorant of how to care for people in such advanced stages of starvation, the soldiers pulled out their C-rations and Hershey bars and gave everything over to the skeletal prisoners, who gorged themselves on the food. Tragically, their digestive systems simply couldn’t handle solid food.

“Decades later, some of these soldiers were racked with guilt over the revulsion they first felt when seeing the prisoners, and then for overfeeding them,” says McManus. “They were killing them with kindness.”

Further compounding the guilt was the fact that the American soldiers couldn't let the liberated prisoners actually leave Dachau. They had to be nursed to health first, which would take months, and then they would need a place to go. Tragically, some of the Jewish prisoners liberated from Dachau languished in displaced persons camps for years before being allowed to emigrate to places like the United States, the UK and Palestine.

Most of the American GIs who liberated Dachau only stayed for a few days before moving on to other missions. The care of the survivors was entrusted to combat medical units, while teams of engineers were charged with burying bodies and cleaning up the camp.

Word of what happened at places like Dachau and Buchenwald spread quickly through the Allied ranks, and many soldiers and officers came to the concentration camps in the days and weeks following liberation to bear witness to the Nazi atrocities. Adolf Hitler committed suicide a day after Dachau was liberated and German defeat was all but assured, but for many soldiers, seeing Dachau for themselves gave the war a new meaning. They weren’t just fighting an enemy; they were fighting evil itself.

General Dwight D. Eisenhower, along with Generals George Patton and Omar Bradley, visited the Ohrdurf concentration camp on April 12, 1945, a week after it was liberated. It was as if Eisenhower knew that the Nazi atrocities of the Holocaust would one day be dismissed as “exaggerations” or denied outright.

“The things I saw beggar description,” said Eisenhower. “The visual evidence and the verbal testimony of starvation, cruelty and bestiality were so overpowering as to leave me a bit sick... I made the visit deliberately, in order to be in a position to give first-hand evidence of these things if ever, in the future, there develops a tendency to charge these allegations merely to ‘propaganda.’”