Fifty years on, many elderly Japanese are reminiscing about the war, but Nobuyuki Abe has more reason to remember than most. As a teenage medical orderly he was dispatched to northern China in the late Thirties, where the Japanese Imperial Army was battling Chiang Kai-Shek's nationalists in the name of the puppet state of Man-chukuo. There he was trained in disease prevention and hygiene, and attached to the Prevention of Epidemics and Water Supply Section of the Imperial Kanto Army, better and more notoriously known as Unit 731.
Abe's ostensible work - supplying clean water and sanitation to the large Japanese garrison in the Manchurian city of Harbin - quickly became subordinate to the unit's real purpose: developing and testing biological and chemical weapons. The Japanese word maruta means "lumber". It was the term used by members of the unit to refer to the prisoners who were used as guinea pigs in live human experiments.
Mr Abe saw Chinese tied to posts in open fields and exposed to poison gas, or injected with syringes of plague bacteria. He dug up graves of plague victims and removed their internal organs for analysis. As a lab technician at Unit 731's headquarters in Harbin, he received samples of bodily organs from branches of the unit in other parts of Manchuria. They were pickled in bottles and labelled with a date and cause of death, and a nationality - Chinese, Korean and, later, Russian, American, French and British. When he joined Unit 731 in 1937, Mr Abe (not his real name) was 13 years old.
Estimates of the numbers of maruta who died vary from 3,000 to 30,000, and the exact figure will never be known. "Unit 731 is the closest thing that Japan has to an Auschwitz," says Ryuji Takahashi, an amateur historian from the northern city of Morioka, who has devoted his spare time to tracking down and interviewing local unit veterans like Mr Abe. But if the horror of the crimes perpetrated by the Imperial Army is comparable to those committed by the Nazis, the attitude of mind towards them is completely different.
Confronted with the growing evidence about Unit 731, successive Japanese governments have displayed a characteristic mixture of embarrassment and paralysis. In 1982, the Ministry of Welfare acknowledged its existence, but denied that human experiments had taken place. A year later the Ministry of Education ordered that a textbook by a Japanese historian must excise passages describing the unit before it could be licensed for use in schools. Ordinary Japanese, however, are less squeamish and, during the symbolic 50th anniversary of the end of the war, there is growing public interest in the activities of the unit. More and more old men like Mr Abe are telling their stories.
An exhibition about the unit, including photographs, eye-witness accounts, and grisly tableaux of human experiments, toured 61 towns and cities earlier this year, attracting 230,000 visitors. "In Morioka alone, 5,000 people came to see it, most of them schoolchildren," says Takahashi. "The most common question was: why didn't grown-ups tell us about this?"
This year, the Education Ministry plans to release a new textbook, which cautiously admits "bacteriological ... experiments on many Chinese and Russians".
The story of Unit 731 did not end with the war. One of the most uncomfortable aspects of the whole affair is the consequences it has for medical knowledge even today. For all their barbarism, the experiments carried out by the Japanese doctors were unique in scientific history. Their primary purpose was military but, by one of the foulest ironies of all, some of the experimental data gleaned from human guinea pigs marked real advances in medical understanding.
Major-General Shiro Ishii, the army surgeon who masterminded and lead the unit, was particularly proud of its discoveries about the mechanism of frostbite. These were made very simply. Human captives were tied to posts in temperatures 20 degrees below zero, and the effects of various remedies were methodically tested on their frostbitten limbs. The "lumber" used in these experiments included a three-day-old baby.
Members of the unit were convicted and imprisoned in China and the Soviet Union but in Japan itself a pall was cast over the whole affair. The occupying US Forces secretly exempted Ishii from prosecution in return for access to his experimental data. Members of the unit served in senior positions in some of Japan's most prestigious hospitals, corporations and colleges, including the National Hygiene Institute, the Medical School of the Ground Self-Defence Forces, and the universities of Tokyo, Kyoto and Osaka.
One goes nervously into an interview with someone like Mr Abe, anticipating tears and distress, a reluctance to rake over terrible memories. But Mr Abe shows no pain or remorse whatsoever: instead, something close to pride. "In Japan we say: the victor is always right, the defeated are always wrong. The things I witnessed were simply a fact of war."