Beneath the pavement lay a massive cache of human remains. The construction crew working at Shinjuku - Tokyo's bustling and prestigious redevelopment site - staggered back, speechless. News of the appalling discovery in 1989 swept across Tokyo like a tidal wave. Unable to conceal the truth any longer, the Japanese government was finally forced to reveal one of the most terrible secrets of World War II. Just metres away from the construction site lay the wartime lab of Lieutenant General Shiro Ishii, father of Japan's top secret biological warfare (BW) programme Unit 731.

The human guinea pigs used in Unit 731's experiments were taken from the base in Manchuria to Tokyo for further study. At the close of the war, the bodies were hurriedly concealed in a mass grave, remaining there until their discovery in 1989. For 40 years, Unit 731's ghoulish activities remained Japan's most closely guarded secret.

Twisted Genius.

The work of the unit could have remained untold had it not been for the discovery in a second-hand bookshop of notes made by a military officer from Unit 731. The documents meticulously detailed the biological experiments, and provided undeniable proof that humans were the test subjects used by Shiro Ishii and his team.

The young Ishii was a brilliant and grandiose Army microbiologist. A flamboyant personality, he soon attracted the attention of senior officers, and was assured rapid promotion. Aligning himself with ultra-nationalists in the Japanese War Ministry, Ishii pushed hard for the development of biological weapons. 

When Japan invaded Manchuria in 1931, Ishii saw his opportunity. it was at Beiyinhe, 70km outside Harbin, that he began his vile experiments on human subjects. Given a large annual budget and 300 men, his first command was assigned the cover name 'Togo Unit'.

Factories Of Death.

Known locally as the 'Zhong Ma Prison Camp', the Unit 731 facility was built by Chinese forced labour. At the centre of the compound, a large building known as 'Zhong Ma Castle' housed prisoners and a human experiment lab. Those chosen for human testing were referred to as 'marutas' - logs. Numbering upwards of 500, the prisoners ranged from 'bandits' and 'criminals' through to 'suspicious persons'. To their surprise, they were well fed and exercised regularly, but even this small humanity was inhumane. Healthy specimens were vital for good scientific results.

The experiments conducted almost defy belief. When Ishii wanted a human brain to experiment upon, guards were assigned to acquire the organ.. Grabbing a prisoner, the guards would hold him down, while another cleaved open his skull with an axe. The organ was clumsily removed and rushed to Ishii's lab, and the remains of the sacrificed prisoner were disposed of in the camp crematorium.

Ishii's first BW experiments focused on contagious diseases such as anthrax and plague. In one test, Chinese guerrillas were injected with plague bacteria. Twelve days later, the infected prisoners were writhing with temperatures of 40 degrees C. One infected victim miraculously survived for 19 days before he was dissected alive.  

Gruesome Experiments.

In later tests, prisoners were poisoned with phosgene gas, others injected with potassium cyanide. Some subjects bucked under 20,000 volts of electricity. Those who survived were later disposed of by lethal injections or autopsied while alive. Every death was closely observed and meticulously recorded by unit members.

The quality of Ishii's work - and the force of his personality - ensured a growing empire. By 1939, he was able to relocate to a massive, dedicated facility. Rivalling in size Nazi Germany's notorious Auschwitz-Birkenau death camp, Unit 731's new headquarters was located at Pingfan, Manchuria.

The Pingfan compound was 6km sq, and housed the administrative buildings, labs, barracks, a prison for human test subjects, and an autopsy-dissecting building. Three giant furnaces handled the disposal of carcasses. A camp at Mukden housed American, British, Australian and New Zealand prisoners of war. Here, too, experiments were performed in secret.

Frostbite experimentation was a particularly important project. Frostbite degraded military efficiency during the bitter Manchurian winters. Echoing similar work conducted by the notorious Nazi, Dr Josef Mengele, naked prisoners were placed in sub-freezing temperatures. they would then have their limbs beaten with sticks until they resounded with a hard, hollow ring - signifying the freezing process was complete. Later, the bodies were 'defrosted' by a range of experimental techniques.

Covering Up The Truth.

Lacking any guilt, Ishii regularly produced scientific papers giving the results of these hideous experiments. Circulated throughout the Japanese medical and scientific community, the papers claimed the tests were carried out on monkeys. Despite this ploy it was an open secret that the real subjects were humans.

By the close of WWII, Ishii - by then ranked a Lieutenant General - bound his subordinates to an oath of secrecy. Pingfan and the other sites were destroyed, and Ishii and his men returned home in obscurity. The chilling activities of Unit 731 remained hidden from public scrutiny.

But in the military and intelligence community nothing is ever forgotten. Despite Ishii's precautions, Allied intelligence had large dossiers on the leading Japanese microbiologists. the US believed they were way behind the Japanese in biological warfare. US military strategists appreciated the tactical benefits - biological agents could be introduced into a war zone covertly. In fact, Ishii had done this on a number of occasions in China and elsewhere.

The Allies were desperate to acquire the expertise and know-how of Ishii's research. Detailed records of the human experimentation were especially sought. Hindered at home by social repulsion to such activities, human experimentation data was viewed as the jewel in the crown. At the end of the war, scientists from Fort Detrick, Maryland, raced to interview Japanese technicians. Barely one of them stopped to consider the ethical implications.

The Secret Of Secrets.

Having assessed the facts, an intelligence cable coldly informed the war department in Washington DC that the 'foregoing information warrants conclusion that [the] Japanese BW group headed by Ishii did violate rules of land warfare'. The message coldly added, 'This expression of opinion is not a recommendation that [the] group be charged and tried as such.'

Anxious to block the Soviets acquiring Ishii's expertise and records, the US discussed a secret deal. But a major obstacle had to be overcome. returning POW's recounted harrowing tales of biological experimentation ruthlessly conducted upon them. If these stories were reported by the press, the public would bray for blood. There was only one option: cover-up.

Prosecutors at the Tokyo War Crimes trials were warned not to investigate too deeply. Allied POW's were sworn to secrecy and cynically forgotten. By 1948, immunity from prosecution was offered to all members of Ishii's unit in exchange for data and co-operation. The biggest cover-up of the war had commenced, and was to last four decades. With the discoveries of the bodies hidden beneath Tokyo in 1989, the true story began to leak out. Eventually, former Allied servicemen started telling of their ordeals.

'Damn right I remember,' Joseph Gozzo snaps angrily. A former aviation engineer living in San Jose, California, USA, Gozzo had glass rods inserted into his rectum during his internment. Gozzo is understandably resentful. 'I can't believe our government let them get away with it,' he says.

Official Enquiry.

Ex-POW, Frank James, shared his memories with a US House of Representatives sub-committee in 1986. 'We were just pawns,' he reflected. 'We always knew there was a cover-up.' Another prisoner, Max McClain, remembers lining up for injections with his bunk-mate, George Hayes. Two days later Hayes complained, 'Mac, I don't know what those sons of bitches gave me, but I feel like crap.' That evening Hayes was dissected at the morgue.

The hearing lasted for just 1/2 a day, and only 1 out of 200 survivors was permitted to testify, incredibly this was the chief archivist for the US Army, saying that files and documents were returned to Japan in the 50's and that copies were not made, as there was no need.

In 1993 the secrecy finally dissolved, what it was promised that all documents pertaining to biological experimentation during the war would be released to the public.