Japan certainly didn't.
Vivisection
Prisoners of war were subjected to vivisection without anesthesia.
Vivisections were performed on prisoners after infecting them with various diseases. Scientists performed invasive surgery on prisoners, removing organs to study the effects of disease on the human body. These were conducted while the patients were alive because it was feared that the decomposition process would affect the results. The infected and vivisected prisoners included men, women, children, and infants.
Vivisections were also performed on pregnant women, sometimes impregnated by doctors, and the fetus removed.
Prisoners had limbs amputated in order to study blood loss.
Those limbs that were removed were sometimes re-attached to the opposite sides of the body.
Some prisoners' limbs were frozen and amputated, while others had limbs frozen then thawed to study the effects of the resultant untreated gangrene and rotting.
Some prisoners had their stomachs surgically removed and the esophagus reattached to the intestines.
Parts of the brain, lungs, liver, etc. were removed from some prisoners.
In 2007, Doctor Ken Yuasa testified to the Japan Times that, "I was afraid during my first vivisection, but the second time around, it was much easier. By the third time, I was willing to do it." He believes at least 1,000 persons, including surgeons, were involved in vivisections over mainland China.
Weapons testing
Human targets were used to test grenades positioned at various distances and in different positions.
Flame throwers were tested on humans.
Humans were tied to stakes and used as targets to test germ-releasing bombs, chemical weapons and explosive bombs.
Germ warfare attacks
Prisoners were injected with inoculations of disease, disguised as vaccinations, to study their effects.
To study the effects of untreated venereal diseases, male and female prisoners were deliberately infected with syphilis and gonorrhea, then studied.
Prisoners were infested with fleas in order to acquire large quantities of disease-carrying fleas for the purposes of studying the viability of germ warfare.
Plague fleas, infected clothing, and infected suppencased in bombs were dropped on various targets. The resulting cholera, anthrax, and plague were estimated to have killed around 400,000 Chinese civilians
Tularemia was tested on Chinese civilians.
Unit 731 and its affiliated units (Unit 1644, Unit 100, et cetera) were actively involved not only in research and development, but also in experimental deployment of epidemic-creating biowarfare weapons in assaults against the Chinese populace (both civilian and military) throughout World War II. Plague-infested fleas, bred in the laboratories of Unit 731 and Unit 1644, were spread by low-flying airplanes upon Chinese cities, coastal Ningbo in 1940, and Changde, Hunan Province, in 1941. This military aerial spraying killed thousands of people with bubonic plague epidemics.
Other experiments
Prisoners were subjected to other experiments such as:
being hung upside down to see how long it would take for them to choke to death.
having air injected into their arteries to determine the time until the onset of embolism. having horse urine injected into their kidneys.
being deprived of food and water to determine the length of time until death.
being placed into high-pressure chambers until death. being exposed to extreme temperatures and developing frostbite to determine how long humans could survive with such an affliction, and to determine the effects of rotting and gangrene on human flesh.
having experiments performed upon prisoners to determine the relationship between temperature, burns, and human survival.
being placed into centrifuges and spun until dead. having animal blood injected and the effects studied. being exposed to lethal doses of x-ray radiation.
having various chemical weapons tested on prisoners inside gas chambers.
being injected with sea water to determine if it could be a substitute for saline.
being buried alive. (Victims included infants.)
“Japan certainly didn’t.”
No they didn’t. They broke many laws, treaties and civilized norms.
BTW China currently does much the same with prisoners. Your reaction?