– Rochester resident Robert Levin is among the last living links to the Manhattan Project and the Atomic Age to which it gave birth.

Levin was a 23-year-old whip-smart Harvard University grad when he was ushered into a room and recruited into a top-secret U.S. government project aimed at developing an atomic bomb. The program was so secret he couldn't tell anybody, not even his wife, and he could be shot for treason if he did.

That was Levin's introduction to the Manhattan Project that would change the world.

"Makes quite an impression on a 23-year-old," Levin told the Post-Bulletin.

Today, Levin is a 96-year-old resident at Rochester's Homestead assisted living facility. He has an amazing memory, recalling events from decades ago with vividness and narrative flow. For nearly two hours, Levin reminisced at length about the Manhattan Project, his work on it and the world it created.

More than seven decades have passed since atomic bombs obliterated Hiroshima and Nagasaki in the last spasms of World War II, killing tens of thousands of people and ending the war. Mankind has since learned to live on this precipice, but fewer and fewer people are acquainted with the pivotal events that shaped the nuclear age.

Levin was not only there at its birth, he helped bring it about.

It would have been nice, Levin says, if Mother Nature hadn't provided the means for making such incredibly destructive bombs, but it did.

And the U.S. had no choice but to open the nuclear Pandora's box that gave rise to the Cold War and mutually assured destruction doctrines, Doomsday Clocks and now a North Korean dictator who threatens to detonate a hydrogen bomb in the Pacific.

"I know it's changed the world, but the point is, there was nothing we could do about stopping that," he said. "You might say, 'well, it was your fault for the atomic bomb, but if we didn't do it, somebody else would have."

Levin was born in Parsons, Kan., and was 2 years old when his family moved to Portland, Ore. He was a straight-A student in high school and went to Harvard on an academic scholarship. His voice is tinged with a hint of disbelief and humor when he recalls paying $400 in tuition at Harvard. Today it is $45,000. Levin graduated with honors in organic chemistry.

Levin suspects he was recruited for the Manhattan Project because he had taken a course in nuclear physics. It was there that he had learned about the incredible destructive power that could be unlocked if somebody figured out how to separate Uranium 235.

It was February 1944 when a man from Union Carbide showed up at the plant where Levin worked with a mysterious proposal.

"He said, 'Mr. Levin, I can't tell you anything about what we're doing, but you have a background that's really beneficial. We think we could use you,' " Levin recalled.

At its peak, the Manhattan Project employed more than 130,000 people, but a much smaller cadre of scientists actually knew they were making a bomb. About 12,000 people worked on the project at the sprawling Oak Ridge plant in Tennessee, but only about 300 to 400 knew its goal.

The bomb was being developed in Los Alamos, N.M., under the direction of Robert Oppenheimer. Levin's job, along with others, was to help produce the Uranium 235 that was converted into metal and sent to Los Alamos for making the bomb.

But would it work? Levin said scientists calculated that the bomb would unleash 20,000 tons of TNT destructive force. Yet it was just the beginning. The atomic bomb would be dwarfed in destructive power by the fusion-dependent hydrogen bombs that would be developed later. The biggest hydrogen bombs the U.S. ever made delivered 20 million tons of TNT, he said.

The first bomb that dropped, on Hiroshima, killed 140,000 people, Levin said. When he heard the news that the bomb had been used, Levin said his response was, "Hooray!"

It meant the war was over.

Levin said he understands that many people will criticize his reaction, but said those who do didn't live in the life-or-death environment that existed at the time. Pearl Harbor and the Bataan Death March had killed thousands of U.S. military members. The American invasion of Okinawa and the ensuing slaughter that took place on the island convinced U.S. leaders that a bloodbath awaited them on Japan.

"None of us that worked there had any feeling like that whatsoever," Levin said when asked about any sense of regret. "Our feeling was: We were in a war. This was live or die. We had to protect our country."

A regular feature of anniversaries marking the bombing of Hiroshima included debates about whether the bomb should have been dropped at all. But those debates faded as the events surrounding World War II receded.

World War II ended, and the Cold War between the Americans and Russians ratcheted up. Levin was sent to Paduchah, Ky., to set up a laboratory for uranium enrichment. Both Oak Ridge and Paducah were thought to be in the Russian cross hairs in the event of a nuclear exchange.

Carolyn McIntosh, his daughter, recalled her father buying and installing in the yard an underground bomb shelter. It had four drop-down cots and shelves for canned food.

"It was a contingency," McIntosh said. "It became more of a tornado shelter than a bomb shelter."

In December 2000, Levin and his wife Vicky moved to Rochester to be closer to their daughter, Carolyn, then a teacher for the deaf and hard of hearing at Rochester Public Schools.

In early 2016, Levin's wife of 73 years died at 95. In the first years of their marriage, the couple had moved 14 times as Levin moved from job to job. Vicky's attitude always was, "OK, it's time to move. Let's get going. I'll decorate them. I'll decorate a new place," McIntosh said.

As a way of coping with grief, McIntosh encouraged him to write a memoir about his life — not just about the Manhattan Project, but also about the amazing things he had seen and done, the historic figures he had met.

"After my mother passed away, my dad spent almost every minute I was with him reminiscing about Mom and the things they did through their lives," McIntosh said. "I couldn't believe how sharp his memories were and how much he could remember."

At 96, Levin hopes for the best, but skepticism and uncertainty nag at him about the future of civilization "if we can't learn to live together," he said. Two thousand years after Jesus offered a model of living in peace and love, he said, "I can't see anyone more peaceful and loving then they were then."

"It's unfortunate that this kind of thing exists, but it does," Levin said. "But the sad part is that we've not learned in all these years to stop fighting each other."