Masahiro Sasaki was only 4 years old when the B-29 bomber Enola Gay dropped its atomic bomb on Hiroshima, wiping out the central part of the city on that sunny Aug. 6, 1945, morning.

In just one moment, the "Little Boy" A-bomb turned the beautiful city into ashes, and about 140,000 people were killed, immediately or in the weeks and months that followed due to radiation exposure.

Sasaki was at home with his 2-year-old sister, Sadako, his mother and his grandmother, just 1.6 km from ground zero.