The bombing hastened the end of World War II. The blast and its aftereffects killed 140,000 in Hiroshima. Three days after Hiroshima, a second atomic bomb was dropped on Nagasaki. That blast and its aftermath claimed 80,000 lives. Japan surrendered six days after the Nagasaki bombing.
Whether the United States should have used the atomic bomb has been debated endlessly.
"I honestly believe the use of the atomic bomb saved lives in the long run," VanKirk said in a 2005 interview. "There were a lot of lives saved. Most of the lives saved were Japanese."
But VanKirk said the experience of World War II also showed him "that wars don't settle anything."
"And atomic weapons don't settle anything," he said. "I personally think there shouldn't be any atomic bombs in the world — I'd like to see them all abolished.
"But if anyone has one," he added, "I want to have one more than my enemy."
VanKirk was teamed with pilot Paul Tibbets and bombardier Tom Ferebee in Tibbets' fledgling 509th Composite Bomb Group for Special Mission No. 13.
The mission went perfectly, VanKirk said. He guided the bomber through the night sky, just 15 seconds behind schedule, he said. As the 9,000-pound bomb nicknamed "Little Boy" fell toward the sleeping city, he and his crewmates hoped to escape with their lives.
They didn't know whether the bomb actually would work and, if it did, whether its shockwaves would rip their plane to shreds. They counted — one thousand one, one thousand two — reaching the 43 seconds they'd been told it would take for detonation, and heard nothing.
"I think everybody in the plane concluded it was a dud. It seemed a lot longer than 43 seconds," VanKirk recalled.
Then came a bright flash. Then a shockwave. Then another shockwave.
VanKirk stayed on with the military for a year after the war ended. Then he went to school, earned degrees in chemical engineering and signed on with DuPont, where he stayed until he retired in 1985. He later moved from California to the Atlanta area to be near his daughter.
Like many World War II veterans, VanKirk didn't talk much about his service until much later in his life when he spoke to school groups, his son said.
"I didn't even find out that he was on that mission until I was 10 years old and read some old news clippings in my grandmother's attic," Tom VanKirk said in a phone interview Tuesday.