Photo/IllutrationHandwriting on this U.S. Army Air Forces’ document dated April 28, 1945, puts Yokohama at No. 3, after Hiroshima and Kyoto, on a list of 17 possible targets for atomic bombing. (Provided by Yozo Kudo)

  • Photo/Illustraion

Recently uncovered U.S. documents might help to unravel the mystery of why Yokohama, once high on the list of possible U.S. atomic bombing targets in 1945, was dropped from consideration.

It may simply have come down to size.

The official reason why Yokohama was spared from a nuclear attack remains unknown, despite the efforts of Japanese historians to uncover details of the selection process for the targets of the U.S. atomic bombs at the end of World War II.

Yozo Kudo found documents at the U.S. National Archives and Records Administration that showed Yokohama was one of the leading candidates among 17 potential targets of the United States.

Kudo, a resident of Yamaguchi Prefecture and head of the secretariat of the nationwide network of groups documenting records of U.S. air raids and damages during World War II, did not find a definitive answer. But the documents shed light on developments leading to Yokohama being taken off the list.

Japanese researchers in the 1970s began examining aspects of the U.S. atomic bombing project, including research and development, the criteria for priority cities and the actual choices of the targets.

At that time, historical documents concerning the atomic bombing in the U.S. archives were being declassified.

Washington started work on selecting possible targets in Japan in April 1945, according to documents published in 1993 by Akira Yamagiwa, professor emeritus at Yokohama City University, and other scholars.

Maj. Gen. Leslie Groves, who oversaw the Manhattan Project that developed the world’s first nuclear weapons, convened the inaugural meeting of the so-called target committee on April 27, 1945. Members of the U.S. Army Air Forces attended.

Four days before the meeting, Soviet troops had advanced to Berlin, and Germany’s defeat in the war was imminent.

Committee members put together “specifications” of Japanese targets at the meeting.

According to declassified documents, the targets should be no less than 3 miles (about 4.8 kilometers) in diameter, be located between Tokyo and Nagasaki and have a high strategic value.

The members also agreed that cities already extensively damaged by U.S. air raids would not be desirable targets.

The U.S. military wanted the atomic bomb--a new weapon that would be used for the first time--dropped on a dense urban center to determine the destructive power of the bomb.

The 17 targets chosen at the meeting included Tokyo Bay, Kawasaki, Yokohama, Nagoya, Osaka, Kyoto, Hiroshima, Yawata (in Kita-Kyushu), Fukuoka, Nagasaki and Sasebo. However, this selection process appeared to involve merely putting large Japanese cities on the list.

Handwriting on a memo uncovered by Kudo and dated April 28, 1945, showed that the possible targets were Hiroshima at No. 1, Kyoto at No. 2 and Yokohama at No. 3.

The memo had been kept by Groves, and Kudo believes the handwriting was that of the Manhattan Project leader.

The committee’s second session, held on May 10-11, studied five cities as well as the Imperial Palace in Tokyo.

For the primary AA-list, Kyoto and Hiroshima were picked. Yokohama was the No. 3 target along with Kokura in Kita-Kyushu on the A-list.

Yokohama was described as an important industrial area that had remained largely intact from U.S. aerial bombings. The city was known as a manufacturing hub of aircraft, industrial machinery and electric equipment, and it had docks and oil refineries, according to the minutes of the meeting.

Production centers were moved from Tokyo to nearby Yokohama after U.S. air raids on the capital intensified, the minutes showed.

At the third session on May 28, the members’ discussions focused on Kyoto and Hiroshima, but Yokohama had been dropped in favor of Niigata.

A large-scale bombing on Yokohama came the following day, on May 29. Some historians say the city’s removal from the list led to the bombing.

But skeptics dispute this theory. They argue that raid on Yokohama involved more than 500 B-29 bombers, and it would have been impossible for the U.S. military to deploy such a large number of aircraft in a short notice within a single day.

Kudo also dug up a “top secret” document dated May 15, 1945, from the headquarters of the 20th Air Force in Washington to the commander of the unit of B-29 bombers in Guam. The document showed that Yokohama was no longer on the atomic bombing target list.

“It is directed no bombing attacks be made against the following targets without specific authorization from this headquarters. These targets are the cities of Hiroshima, Kyoto and Niigata,” the memo read.

Kudo speculates that Yokohama was removed because it apparently did not meet one of the conditions for the atomic bombing.

“Yokohama stretched along the coast, and its urban center was only about 4 kilometers wide back then,” he said. “So, I think that the city did not match the criteria for a desired target of at least 3 miles in diameter.”

Another theory is that U.S. forces believed Yokohama was equipped with more anti-air defense units than other Japanese cities.

U.S. forces were particularly concerned that the aircraft carrying the atomic bomb might be forced to return to its base without dropping its payload, and it could lose the bomb on the way.

At the insistence of War Secretary Henry Stimson, Kyoto was removed from the list. Stimson feared that Japan could side with the Soviet Union out of fierce resentment toward Washington for destroying Japan’s cultural center.

As a result, Hiroshima became the No. 1 target, followed by Kokura.

The world’s first atomic bomb was dropped on Hiroshima on Aug. 6, 1945.

Three days later, the second atomic bombing mission headed to Kokura, but poor visibility of the city forced the bomber to drop the weapon on Nagasaki instead.

Among the criteria laid out by the target committee was to visually release the atomic bomb on a targeted city to achieve the most effective use of the bomb.

***

CORRECTION

This article was revised on June 17. The 23rd paragraph of the article originally said: “Some historians say the large-scale bombing on Yokohama the following day, on May 29, led to the city’s removal from the discussions.”