Lincoln. Neb. ? Sixty years after the Enola Gay dropped the world’s first atomic bomb attack over Hiroshima, a Nebraska physicist who helped develop the weapon said he has no regrets.

“We did what we set out to do. I was just doing my job. It was war. You got used to it after awhile,” said Theodore Jorgensen, who worked with the Manhattan Project while on a leave of absence from the University of Nebraska.

Jorgensen, 99, was there to witness the world’s first nuclear bomb test, which rocked the New Mexico desert near Alamogordo in the summer of 1945.

“We knew we were on the edge of a new world,” Jorgensen said.

Three weeks after the test, the bomb was dropped on Hiroshima. But Jorgensen said the scientists knew immediately after the test the bomb would end World War II.

“We realized a lot of people were going to get killed, and I think everyone regretted that,” Jorgensen said. “But we essentially knew the war was over that day.”

Officials estimate that about 220,000 people were killed instantly or died within a few months after bombs were dropped first on Hiroshima and then three days later on the Japanese city of Nagasaki. Japan surrendered on Aug. 15, 1945, ending World War II.

Hiroshima officials now put the total number of dead in the city alone at 242,437, which includes people who were initially listed as missing or who died afterward from a loosely defined set of bomb-related ailments, including cancers.

Jorgensen said the bomb may have prevented a full-scale U.S. invasion of Japan to end the war, which would have resulted in massive casualties on both sides.

“A relatively large number of people have come up to me in past years to say they appreciate the fact that they are alive today because of what we did,” Jorgensen said.

His first task with the Manhattan Project, which took him to the University of Chicago and then Los Alamos, N.M. – where the bomb as designed and assembled – was to devise a way to measure the size of the impending test explosion. It was a challenge, he said, because the world had never seen anything like it.

“Some people thought the universe would blow up,” said Jorgensen, who lives in Lincoln. “Cooler heads knew pretty well what was going to happen.”

His measurement turned out to be fairly precise, he said. One day after the blast, Jorgensen said he probably became the first person in history to observe and measure the radioactive fallout from a nuclear explosion.

Jorgensen doesn’t consider his work to have been significant to the famed project.

“I didn’t make any great contributions,” he said.