05-08-2025
‘Mock Atomic Bombs' Dropped Across Japan Near War's End; Hundreds Killed in Missions to Test Trajectory, Boost Accuracy
'Mock atomic bombs' were dropped across Japan in July and August 1945, just before the end of World War II, to test their trajectory and thereby improve the accuracy of the devastating bombs that would ultimately be unleashed on Hiroshima and Nagasaki.
Forty-nine such bombs — each weighing 4.5 tons, nearly the same weight as the 'Fat Man' bomb released over Nagasaki — were dropped on 18 prefectures. They contained conventional explosives but had enough power to create craters upon impact.
About 400 people are said to have died in these bombings. Bereaved families say the damage caused by the atomic bombs is not limited to Hiroshima and Nagasaki.
'No remains were found, just a deformed coin purse,' said Yoshiaki Matsuura, 88, from Otsu. He was remembering the day 80 years ago when his older sister, Haruko, then 16, was killed by a mock atomic bomb.
Haruko was the eldest of eight children. Matsuura remembers how she would go into the yard in a white apron and call out to her siblings, 'Lunch is ready!'
Haruko attended a local girls' school. On the day of the air raid, she was working at the Toyo Rayon Co.'s Shiga Plant — now the Shiga factory for Toray Industries, Inc. — 2.5 kilometers from her home.
A U.S. B-29 bomber dropped a mock atomic bomb on the plant on the morning of July 24, 1945. The building was blown to pieces, and a fire broke out.
Her family searched for Haruko at the factory and her school, but her whereabouts remained unknown. Six months after the air raid, the family got a call from the plant. Matsuura went there with his mother and brother and found a coin purse that Haruko had used among the belongings of the victims.
The purse was originally decorated with red beads, but it had turned purple and was bent out of shape, apparently due to the fire. Her remains were never found, so the purse was placed in her grave as a keepsake. The air raid is said to have killed 16 people and injured over 100.
Matsuura himself was also caught in an air raid during the war. Born with a disability in his hip joint, he cannot move quickly. Even so, every time an air raid siren sounded, he had to evacuate to a safe place. After the war, he struggled to make ends meet, eating nuts and begging at the station to survive. His younger sister died of malnutrition.
Even amid his hardships, he never forgot about Haruko.
About 20 years ago, Matsuura was told by a researcher that the bomb destroyed the Shiga Plant was a 'practice bomb.'
'I never imagined it was a bomb connected to the atomic bomb,' he said in shock. 'It's ordinary citizens who bore the brunt of the war. We lost our loved ones and had our lives shattered.'
Civil group sheds light
A citizens group in Aichi Prefecture eventually shed light on the existence of the mock atomic bombs, which had been buried in history since the end of the war.
The group to record World War II in Kasugai, Aichi Prefecture, was formed in 1986 by middle school teachers and others. Members scrutinized a U.S. military report that surveyed the effects of the bombing of Japan, trying to learn more about the Aug. 14, 1945, air raid on Kasugai.
The group found the term 'Special 17' in the margins of the report. The atomic bombs dropped on Hiroshima and Nagasaki are known among researchers as 'Special Mission 13' and 'Special Mission 16.'
Group member Tsutomu Kaneko, 74, intuitively felt that 'the air raid on Kasugai and the atomic bombs were connected.'
In 1991, Kaneko discovered a list of sortie missions and maps for the 509th Composite Group, a special unit formed by the U.S. military to drop the atomic bombs, at the National Diet Library, Japan. The documents referred to 'Special Missions,' listing Hiroshima and Nagasaki alongside locations in Kasugai.
When conducting research at an air force base in Alabama, Kaneko also discovered the 509th Composite Group's special mission report detailing its bombings.
Yozo Kudo, 75, a member of an association to record air raids and war damage across Japan, eventually joined the investigation. They discovered that B-29 bombers had carried mock atomic bombs of the same shape and weight as the actual ones and conducted secret training missions over Japan.
Kaneko's civil group revealed that a total of 49 bombs were dropped across 18 prefectures, and identified the impact points of 46 of them.
'I want many people to remember that the first nuclear weapons were used in Japan, and various regions across the nation served as testing grounds,' Kaneko said.
Kudo said, 'We can understand the overall plan behind the A-bombings by learning about the 49 mock bombings.'
