An aerial photo shows that U.S. forces knew of Kurayoshi Airfield, one of dozens of "secret" airfields that the Imperial Japanese Army built during the final stages of World War II. (Shun Suzuki)

KURAYOSHI, Tottori Prefecture--A former airfield here secretly built by the Imperial Japanese Army during the final stages of World War II turns out not to have been so secret after all, according to new research.

"It's likely that most of the secretly built airfields in Japan were detected and surveyed by U.S. forces (at the time)," said Yozo Kudo, 69, a former professor at the National Institute of Technology, Tokuyama College, who conducted the research.

The airfield is among dozens that were constructed by the Japanese side in a last-ditch preparation for an expected invasion of the mainland.

Kudo obtained in April an aerial photo of Kurayoshi Airfield taken Aug. 6, 1945, that was stored at the U.S. National Archives and Records Administration.

According to a report attached to the photo, it was taken by an F-13 reconnaissance plane belonging to the 3rd Photo Reconnaissance Squadron of the U.S. Army Air Corps on the day from an altitude of about 9,500 meters.

The report stated that there was no sign of aircraft around the airfield, which was located in Kurayoshi, Tottori Prefecture; bomb shelters to protect aircraft from enemy attacks; or aircraft parking aprons.

The photo is captioned "Kurayoshi Airfield" and assigned a code, meaning that U.S. forces likely knew about its existence before the mission to take aerial photos, according to Kudo.

The report also mentioned the following: "At 8:17 a.m., an explosion is observed in the Kure area. Two pillars of smoke shot up to as high as 35,000 feet."

The description apparently refers to the atomic bombing of Hiroshima at 8:15 a.m.

Kudo believes that the squadron flew to the area above Kure, Hiroshima Prefecture, after it photographed Kurayoshi Airfield.

As the war situation worsened and a potential "homeland defense war" drew near, the Imperial Japanese Army hastily and secretly built about 40 airfields around the nation.

It is known that several such secret airfields were detected and surveyed by U.S. forces, and their aerial photos remain extant today, each assigned a code similar to the photo of Kurayoshi Airfield, Kudo said.

Kudo, who has studied air raid situations extensively and published many works, learned about the U.S. forces' reconnaissance mission over Kurayoshi Airfield in 2011.

Kudo found the photo in question while going through piles of archived aerial photos that U.S. forces took during the war.

"While there is no such document in Japan, U.S. forces kept detailed records, based on which we can gain insight into the situation in Japan in those days," Kudo said.

'RED DRAGONFLY'

Today, the Kurayoshi Airfield site is completely covered with rice fields. Part of a prefectural road runs straight through the former top-secret military site, which straddles the Yokota and Shimoyonazumi districts of Kurayoshi.

Local resident Kiyoshige Yamane, 79, remembers a day in 1945, just before the end of the war, when 10 or so biplanes entered the airspace above and landed at the airfield.

“They were very cool,” Yamane recalled.

The planes had two wings on top and bottom—a particular type of aircraft nicknamed the “red dragonfly” at the time.

“'Red dragonflies' were flying together against the backdrop of Mount Daisen,” Yamane said.

He remembers that construction of the airfield began around May 1945.

Workers reaped barley grown in the area to widen the prefectural road, which was so narrow that a bus could barely pass through.

Yamane’s older sister, Chiseko Furuichi, was forced to help with the construction by carrying stones with her classmates when she was a third-grade national elementary school student.

“There were only women and children,” Furuichi, now 83, recalled.

The heat was unbearable, and they risked their health to work under such conditions.

“But there was no way for us to complain,” Furuichi said.

Residents referred to it as “Takashiro Airfield,” after a local village by the same name, instead of Kurayoshi.

According to Yamane, the biplanes were hidden in a hangar built in a nearby bamboo forest as soon as they landed, and never ended up taking off.

The planes remained there after the war, open to anybody who happened upon them. They became a favorite playground for Yamane and his cousin, who dangled from the wings and sat in the cockpit.

“In retrospect, all of the aircraft were old,” Yamane said.

He wondered, “Would these planes have been used for a kamikaze mission if Japan had entered a homeland defense war?”

The biplanes may have looked simply cool to children, but in reality, they played a central role from World War I until the 1930s.

As of 1945, they were long obsolete and belonged to the previous generation in terms of both speed and performance.

'INSANITY OF WAR'

In May 1945, three months before Japan surrendered, the Imperial Japanese Army began construction of secret airfields, according to Yoshimasa Nishimura of the Tottori prefectural archives.

Nishimura, a 50-year-old modern history specialist, said that the purpose was to decentralize the air force power and set aside as many aircraft as possible for the inevitable invasion of U.S. forces.

According to Nishimura and other military-related documents, there were already airfields in Tottori and Yonago in the prefecture, and kamikaze fighter planes used for suicide missions and training planes were deployed there.

“But the existence of these two airfields was already well known to U.S. forces and they were highly likely to be airstrike targets,” Nishimura said.

“That is most likely why Japan’s former Imperial Army set their sights on Kurayoshi,” Nishimura explained.

The army funneled manpower and hastily constructed these airfields and believed they were kept out of sight of U.S. forces.

“It was one example of the insanity of war,” Nishimura said about the Japanese side's operations toward the end of the war.

About 10 years ago, Yamane started interviewing elderly residents who were mobilized to work on the construction of the airfield.

As the existence of a “secret airfield” was not well known among the locals, Yamane was afraid that the history would be lost.

“My sister, my family--everybody was forced to work there without being told why. I want young people to know about the recklessness of it all,” Yamane said.