My grandpa was there for this. He was a Dutch Soldier captured by the Japanese held as a prisoner of war. They had him doing hard labor underground in a coal mine in Hiroshima. When the bomb dropped, everyone in the mine evacuated, believing there was an earthquake happening. Even though he fought gruesome battles, even though he faced tortures / brutalities under the Japanese, it was the melting faces at Hiroshima that consistently haunted him during in his dreams.

Later they moved the POW labor to Nagasaki. They were kept on the outskirts of the city so were safe but still witnessed the second blast. When it happened, the house they were in collaped on him.

He had fought the Boer War for the Dutch. Even captured the regiment that Churchil was with, but luckily released them.

Later in WW2, he fought to protect the Dutch colony in Indonesia from the Japanese - but lost, e.g. the nuclear experiences in Hiroshima and Nagasaki.

As far as health effects go, he seem to have suffered effects of radiation and also black lung from all of the coal mining. He died in the late 80s and the story in my family goes like this:

Some government scientists showed up at the house to ask his wife if they could autopsy him for research. Later, when the results were given to my family, we found out that all of his bones were slightly blue-tinted and curved. It is not suspected that this strange effect on his skeleton was caused by the radiation exposure, and that the mysterious pain he constantly experienced was a result of this odd deformation.