NHK has obtained a document from more than six decades ago that praised the United States and Japan for their handling of a little-known radiation exposure incident involving two Japan Coast Guard ships.

A secretary at the US Embassy in Tokyo, Richard Snyder, wrote the document two months after the incident took place in July 1958. He later became a deputy assistant secretary of state.

The vessels Takuyo and Satsuma were sailing in the Pacific when they were exposed to fallout from a US hydrogen bomb test at Bikini Atoll.

Takuyo's chief engineer Nagano Hirokichi died of leukemia one year later. But experts concluded that the amount of radiation to which he was exposed was so minimal that it was difficult to connect it to his death.

Snyder wrote that the US did not make light of the radiation exposure claim and sent doctors to Rabaul in Papua New Guinea. He also wrote that Japan regarded this action as evidence that the US cared about the crew.

Snyder added that Japan tried to avoid clashes with the US even before a probe into the incident wrapped up.

He wrote that in his opinion, Japanese people held deep-rooted views that US nuclear tests were unpleasant and potentially harmful to humans, but they seemed to think that such tests were inevitable.

The diplomat also wrote that some people even apparently came to a conclusion that nuclear tests were justified in light of the international situation.

Snyder added that Japanese people had come to believe that their protests against the US had no impact at all, and instead had an undesirable effect on bilateral relations.

Kyoto University Professor Moriguchi Yuka says the document is important because it sheds light on how the US government analyzed the incident.

She also says the two countries tactfully disclosed information so that it would not spread widely, and that they succeeded in downplaying the seriousness of the incident.

She adds that this manipulation of the information caused the case to fade from the public eye.