Six of the most disturbing "experiments" conducted by Unit 731, the gruesome biological and chemical warfare research unit of the Imperial Japanese Army.

World War II was beyond horrible for hundreds of millions of people. It’s as if all the developed countries of the world had surplus rage and hate that they had been storing up, and it all came flooding out in the war years.

Out of all the areas in which World War II was fought, none were active as long as what would come to be known as the Pacific Theater. In fact, Japan arguably started the war by attacking Manchuria in 1931, and it inarguably waged war with China by invading in 1937.

The disturbances and upheavals that these invasions caused shook China to its very foundations, triggered a civil war and a famine that probably killed more people than currently live in Canada and Australia combined, and lasted until the country’s Soviet “liberation” in 1945.

And out of all the outrages that Imperial Japan unleashed upon the Chinese people during this brutal occupation — and there were indeed some stunning crimes committed, even by World War II standards — probably none was as gratuitously hateful as the operations of Unit 731, the Japanese biological warfare unit that somehow plumbed new depths in what was already a nearly genocidal war.

Despite innocent beginnings as a research and public health agency, Unit 731 eventually grew into an assembly line for weaponized diseases that, if fully deployed, could have killed everyone on Earth several times over. All this “progress” was, of course, built on the limitless suffering of human prisoners, who were held as test subjects and walking disease incubators until Unit 731 disbanded at the end of the war.

In a long list of atrocities, these six programs, in particular, stand out in the bloody history of Unit 731:

Unit 731 Experiments: Frostbite Testing

Yoshimura Hisato, a physiologist assigned to Unit 731, took a special interest in hypothermia. As part of Maruta’s study in limb injuries, Hisato routinely submerged prisoners’ limbs in a tub of water filled with ice and had them held until the arm or leg had frozen solid and a coat of ice had formed over the skin. According to one eyewitness account, the limbs made a sound like a plank of wood when struck with a cane.

Hisato then tried different methods for rapid rewarming of the frozen appendage. Sometimes he did this by dousing the limb with hot water, sometimes by holding it close to an open fire, and other times by leaving the subject untreated overnight to see how long it took for the person’s own blood to thaw it out.