Family members said Jeppson died March 30 at a hospital in Las Vegas after being hospitalized for back pain and a severe headache, The Washington Post reported.
Jeppson, known as "Dick," was a 23-year-old Army Air Forces second lieutenant when he flew his only combat mission aboard the Enola Gay, which dropped the bomb Aug. 6, 1945, leading to the Japanese surrender and the end of World War II.
The bomb had to be armed in flight to prevent accidental detonation during the plane's takeoff. Jeppson, the weapons test officer, armed the bomb's electrical system, pulling out safety plugs and replacing them with firing plugs. His boss, Navy Capt. William S. Parsons, installed the charge that would be fired into the weapon's uranium core.
Jeppson would later recall the flash as the bomb exploded.
"No joy at that point," he told Time magazine in 2005. "But it was a job that was done."
After receiving the Silver Star, Jeppson worked as a civilian in electronics and applied radiation.
He was born in Logan, Utah, June 23, 1922, and joined the Army Air Forces, hoping to become a pilot. But after he failed the vision test, the military sent him to electronics and radar training programs at Yale, Harvard and the Massachusetts Institute of Technology.
Jeppson received a bachelor's degree in physics at the University of California, Berkeley, and worked for the university's radiation laboratory and at the Lawrence Livermore National Laboratory. He then founded two companies -- one that built linear accelerators and another that made industrial microwave ovens.
He had lived in California before moving to Las Vegas about 20 years ago.
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