As all the prisoners of Unit 731 were killed, and the employees swore secrecy about the experiments, first-hand testimonies are very hard to come by.

Yoshio Shinozuka, 69, of Yokaichi City, east of Tokyo, was a 15-year-old Imperial Army Youth Corps cadet when he was assigned to Unit 731 in Manchuria in May, 1939. He stayed with the unit until August, 1943.

After the war, he remained with an active unit in China, was arrested there in 1952 along with other former Unit 731 members and detained until 1956 without being prosecuted.

He said he had been assigned to a germ-producing section of Unit 731 which had experimented mostly with rats, and also had been involved with epidemic prevention research.

From time to time, more experienced Youth Corps members were asked to help with human experiments although security was tight and secrecy obsessive.

“There was a special cell (for human experiments) which had a window but it was almost impossible to see in,” he said. “It had iron doors which were always locked and guarded. To get in, you needed special permits and a pass with a photograph, and the entrance and exit times were recorded. It was very strict.

“Towards the end of my time with the unit I went in twice when maruta experiments were being conducted. The two people seemed to have just died and had been opened up.

“My job was to collect parts containing the bacteria and put them in a glass case . . . for confirmation of how far the disease had spread through the body.”

Mr Shinozuka said that after four years of training with, and “brain-washing” by, the unit, he knew what was happening at Harbin and was not surprised at what he saw in the cell. He had not even felt guilt at being part of it.

It was only after the war, when he was in custody of the Chinese, that he had become aware of the full horror of Unit 731’s activities.

“Before the war, we were told we’d have to fight to protect ourselves, our families and the Japanese people.

“When we were detained by the Chinese, we found the authorities treated us humanely, whereas I saw our treatment of them had been inhumane. We were surprised,” he said.

“That’s one reason I’ve decided to speak out. The other is that what really happened with Unit 731 had to be made public so that it will never be repeated. Our young people have to be told the truth.”