Norman Mayor, 91, of Dresher, a chemist and World War II veteran who helped the U.S. military build the atomic bomb, died Friday of natural causes.

Mr. Mayor was drafted into the Army in 1944, thinking he was going to be sent to Bellingham, Wash., and eventually to the Pacific Theater, his daughter Alisa Mayor said Sunday.

Instead, after completing training in Texas, he and a group of other chemists were told to report to Knoxville, Tenn. "Then they were told to wait on a certain corner and a certain street," Alisa Mayor said.

"They didn't know why they were there," daughter Sandra Pachuta said. A truck came and took the chemists to Oak Ridge, Tenn., where they were told to mix certain chemicals, which were described to them only as "A" or "B," Pachuta said.

But Mr. Mayor soon realized he was working with "explosive chemicals," she said. "He and his fellow cohorts started realizing that."

He may not have known it at the time, but Mr. Mayor was contributing to the United States' covert Manhattan Project, which sought to build the first atomic bomb. Personnel in Oak Ridge, like Mr. Mayor, worked to enrich uranium for the bomb.

President Harry S. Truman ordered the bombs dropped on the Japanese cities of Hiroshima and Nagasaki in 1945 after Japan refused to surrender to Allied forces. The decision, which effectively ended the war, prompted significant controversy, but Mr. Mayor felt proud of the work he did, his daughters said.

Had the United States not resorted to nuclear weapons, it likely would have invaded Japan, a course some historians say would have cost more lives.

"If the bomb had not dropped, the amount of devastation would have been so many more lives lost," Pachuta said. "He feels it was a necessary evil in a way. They just needed to end what was going on."

Mr. Mayor later received a certificate from the Army acknowledging that he had "participated in work essential to the production of the atomic bomb."

Mr. Mayor was born Dec. 16, 1921. He grew up in West Philadelphia and attended Overbrook High School and then the University of Alabama at age 16. After the war, he started his own chemical business in Philadelphia and manufactured a compound that prevented steel from rusting, family members said. He sold his product to Bethlehem Steel and other clients, they said.

Family members described Mr. Mayor as having an entrepreneurial spirit. "He had a brilliant mind," Pachuta said. "He was a man for all seasons."

In addition to his daughters, Mr. Mayor is survived by his wife of 46 years, Phyllis; son-in-law Christopher Pachuta; and a granddaughter, Audrey Pachuta.

The funeral will be held at 3 p.m. Wednesday, Dec. 26, at Joseph Levine & Sons, 4737 Street Rd., Trevose. The family requests contributions to the charity of the donor's choice.

Contact Andrew Seidman at 856-779-3846, aseidman@phillynews.com, or follow @AndrewSeidman on Twitter.