Photo/Illutration A letter written by a second-class petty officer of the Imperial Japanese Navy about the “kaiten” human-piloted torpedo (Provided by the Kaiten Memorial Museum)

SHUNAN, Yamaguchi Prefecture--A letter written in 1944 shows that word had leaked about a top-secret human-piloted suicide torpedo program to even lower-ranked military personnel.

The letter, written by a second-class petty officer and addressed to his family, was found at the Kaiten Memorial Museum on Otsushima island here.

The petty officer would later serve as a maintenance worker of “kaiten” torpedoes used by the Imperial Japanese Navy in suicide missions to sink enemy vessels.

The letter states that he would be deployed to the No. 1 special base in Kure, Hiroshima Prefecture, which was used for kaiten before its successor was set up on Otsushima.

“I cannot even imagine what I will be ordered to do there, but the duty will not be safe,” the petty officer wrote. “Everyone says the base involves special submarines or human-operated torpedoes.”

The content of the letter indicates it was penned on or before Sept. 1, 1944, when the training base became available on Otsushima.

The kaiten plan was officially announced in March 1945, four months after the suicide unit swung into action.

The letter shows that some details of the weapon had already leaked.

“Although the development of kaiten was kept secret, a rumor circulated among navy noncommissioned officers that human torpedoes were being created,” said Hidekazu Misaki, a researcher at the museum.

The letter was discovered when the museum was sorting 1,300 items for digital formatting, a project under its digital museum system that cost 11 million yen ($102,400).

While the start of operations of the digital system had been postponed because of the novel coronavirus pandemic, the letter and many other articles were made available on July 2 on a 50-inch touch panel.

Computerized items on display are categorized into “messages by and possessions of the deceased,” “kaiten-related materials” and “image and sound records.” That way, the showpieces can be searched by the names and hometowns of the service members who worked at bases in Otsushima, Hikari and elsewhere.

Letters are stored in chronological order based on their postmark dates, allowing visitors to understand how the feelings of military personnel changed over time. All images except photos taken for memorial purposes can be enlarged.

Of the 1,300 items, only 300 are exhibited to the public at the museum.

“Materials that cannot be exhibited due to space restrictions can be viewed under the digitized system,” Misaki said. “I recommend that visitors actively use it."

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