An engineer recruited to work on the Manhattan Project says he opposed the use of nuclear weapons on civilian targets and believes the United States “could have waited” before A-bombing Nagasaki, given that the Japanese government was in turmoil from the destruction of Hiroshima and the war might have ended without the second city’s destruction.

James Schoke, 91, made the comments during a recent interview at his home in Florida ahead of the opening Saturday of an exhibition in Washington to commemorate the 1945 atomic bombings of Hiroshima and Nagasaki.

The secret project to produce the world’s first atomic bomb involved about 125,000 scientists, engineers, service members and others when it was in full swing. While some are known to have voiced misgivings about using the A-bomb in war, Schoke’s remark suggests the apprehension was shared by the engineers and technicians who worked first-hand on developing the weapons.

Schoke was a student at the Illinois Institute of Technology and was later sent to the University of Chicago’s Metallurgical Laboratory, one of the central institutions in the project. Assigned to the instrument group there, he was tasked with helping scientists primarily by improving radiation detectors.

Regarding the first A-bomb attack on Aug. 6, 1945, Schoke said: “I was opposed to dropping on Hiroshima. I didn’t like it.”

The project led to the world’s first atomic detonation at Alamogordo, New Mexico, a few weeks before Hiroshima.

“We knew it was a horrendous weapon and that there would be many people killed,” Schoke said.

He said the atomic bombing of Nagasaki on Aug. 9 “upset” him.

“Because there was such turmoil in the (Japanese) government (after Hiroshima), they should have given a little time for them to get themselves together. We didn’t have to do it three days later, we could have waited 10 days,” he said.

Along with others working on the project, Schoke signed a petition drafted by physicist Leo Szilard, whose research and warnings initiated the project, to President Harry Truman calling for demonstrating the weapon only. Technical errors meant Schoke was not listed as one of the cosigners.

Schoke shares the view that the A-bombs helped save the lives of many U.S. soldiers and also accepts that dropping a bomb on a wholly military target is an option in war.