TOKYO (Kyodo) -- An Army surgeon involved in U.S. nuclear weapons development repeatedly warned about the impact of radiation on humans, but the Manhattan Project site chief sought to downplay the danger to manage public perception of such weapons, his grandson said.

Working as a radiologist during the Trinity test in New Mexico, Surgeon James F. Nolan became aware of radiation's impact on humans through pre-tests. In June 1945, he submitted a report directly to Army Gen. Leslie Groves, aiming to raise concerns about the health risks of nuclear weapons, according to the surgeon's grandson, James Nolan Jr.

"Groves was primarily concerned with issues related to security and secrecy. And therefore, health and safety matters were entirely secondary for him," the Williams College professor said in a recent online interview with Kyodo News.

The Army general eventually agreed to implement some safety measures and evacuation preparations but continued to dismiss warnings from his subordinates, the grandson said.

When asked why Groves was reluctant to acknowledge health issues related to nuclear weapons, Nolan Jr. said, "I think that his concern was that it could look bad for the Manhattan Project. And there was a general sense that chemical and biological warfare was wrong. And in the same way, you could say that these ongoing effects of radiation were in the same category as chemical and biological warfare.

When he managed to have a chance to sit down with the Army general to discuss the matter, Groves called him "a propagandist."

According to the professor's research, two days before the world's first nuclear test on July 16, James Nolan departed for the Pacific island of Tinian, carrying highly enriched uranium intended for the Hiroshima atomic bomb.

The purpose of his trip to Tinian was to oversee the health of personnel involved in transporting and assembling nuclear bombs, according to Nolan Jr.

On Sept. 9, about a month after the first atomic bombing, he entered a devastated Hiroshima as part of a U.S. military research team.

During the visit, the research team witnessed people still dying from radiation exposure and reported their findings to Groves. However, in his congressional testimony in Washington at the end of November 1945, Groves completely denied the severe suffering caused by radiation to A-bomb survivors.

During the interview, Nolan Jr. recounted the anguish of his grandfather, who visited Hiroshima and Nagasaki as part of the Manhattan Project research team following the atomic bombings.

During his lifetime, the military surgeon did not share his thoughts or anguish about his experiences, according to Nolan Jr., who extensively researched his grandfather's life and spent time studying in Nagasaki.

"I have to tell you that I never once talked to my grandfather about his experience on the Manhattan Project. He was very quiet about it."

"I think it really troubled him, what he saw, what he'd been a part of, and talking to family members, including his daughter, they agree that it was something that he really wrestled with," the grandson said.

However, James Nolan once described the devastation of the A-bombed areas to one of his nephews, saying, "It was utter devastation which you can't even imagine."

After the war, the military surgeon observed nuclear tests in the Marshall Islands in the Pacific Ocean and monitored the effects of radiation. Upon learning that an atmospheric nuclear test had also been conducted in Nevada, he shook his head and said, "They have no idea what they're doing."

Based on the advice of the Radiation Safety doctors, including James Nolan, who were in the Marshall Islands in the summer of 1946, a nuclear test called Charlie was canceled.

IN discussing the consequences of the August 1945 atomic bombings, the grandson shared his perspective based on his conversations with atomic bomb survivors.

"It's not something that ended in 1945. It's something that has continued. And I think it's important, particularly for Americans, to understand that. To appreciate that."