Memories of a long-demolished weapons laboratory are being revived to great interest as a documentary about the secret facility lets former workers give a rare glimpse into Japan’s covert actions during the war.

The history of the Noborito Laboratory, formally called the 9th Army Technical Research Laboratory, had been shrouded in mystery because records of the institution were largely destroyed at the end of World War II.

The workers at the lab stayed mum about their experiences long after the war, until some were persuaded to go on record for the film, “Army Noborito Laboratory.” The film, which was aired in Tokyo in August, has proved unusually popular for movies of its kind and is scheduled for release in other parts of Japan.

“I remained silent because of my sense of guilt,” said Enji Ota, 85, one of the roughly 40 former workers who divulged their wartime memories for the film. “I’ve come to think, however, I must tell young people that we must not go to war again.”

Ota worked at the laboratory as an apprentice engineer in 1943 and was involved in the “balloon bomb” project.

The balloon bomb, one of the most exotic inventions of the Noborito lab, was a free-floating hydrogen balloon that carried a bomb. The idea was to take advantage of the jet streams over the Pacific Ocean to float bombs all the way to the U.S. mainland.

In the last two years of the war, around 9,000 balloon bombs were sent aloft from coastal areas of the eastern prefectures, including Fukushima, Chiba and Ibaraki.

Some reached the U.S. mainland and caused casualties.

“We were told not to say anything to anybody — even our parents and siblings — about what we were doing at the lab,” recalled Ota, who was 15 at the time.

For him, memories of the lab include innocent moments, like the sweet bean paste buns that used to be doled out to employees after successful balloon bomb launches.

All the same, he kept the memories to himself.

Two years ago, Ota, who started a real estate business after the war, was asked to discuss his experience at the Noborito lab in the film, and eventually agreed.

The Imperial Japanese Army built what would later become the Noborito lab in Kanagawa Prefecture in 1937 to develop weapons, including biochemical agents.

It also worked on equipment used for spying and other covert operations.

At its peak, 1,000 people were employed at the lab.

As the American bombings of Japan intensified toward the end of the war, the lab’s operations were transferred to various remote locations.

Another former worker who appeared in the film, Nobuo Igarashi, 95, said he joined the lab as an expert in dyeing techniques.

His skills were exploited for the development of an ink used to print counterfeit Chinese bank notes. In all, the Noborito lab churned out about ¥4 billion to ¥5 billion worth of fake Chinese bills.

The bills were taken to Shanghai by operatives of the Nakano School, a military intelligence training institution, during an operation aimed at disrupting the economy in the parts of China that were under the control of Chiang Kai-Shek.

Igarashi said his job at the lab was “not a matter of pleasure or justice; I was working hard to survive.”

The former workers of the Noborito lab escaped war crimes charges after the war, just like those who were involved in the Imperial army’s infamous Unit 731 — which is notorious for having used human guinea pigs to develop chemical and biological weapons and for carrying out live vivisections on prisoners — did.

Afterward, many former Noborito lab workers were recruited by the U.S. military to assist in clandestine activities, such as forging public Chinese and North Korean documents during the Korean War.

Igarashi also worked at a U.S. military facility for a while, before starting to work for an ink manufacturer.

“Looking back, my life seems to have always been haunted by the experience of Noborito,” he said. “But I don’t think myself to be an unlucky man. That was the way of life in those days.”

Tadayuki Kusuyama, the director of “Army Noborito Laboratory,” spent more than six years completing the film.

Kusuyama is hoping the film will provide the opportunity to reflect on the war.

“What was that war for? I want (viewers) to face up to this question through the film,” he said.

KEYWORDS Wartime, weapon, lab