At 8:12 in the morning, Oka’s station detected the Enola Gay directly over the city. By the time her station manager authorised the air raid warning, it was too late. The bomb was dropped at 8:15 and detonated in the air. Even behind two thick walls of reinforced concrete, Yoshie was thrown back by the blast and knocked out. When she awoke moments later, she went outside into the fog and asked a wounded soldier what had happened. Then she went back to the bunker, found a working phone, and gave the world’s first report of Hiroshima. Repeating the soldier’s words, she told the call centre in Fukuyama, “A new type of bomb was dropped.”

Watch Yoshie's harrowing testimony - courtesy of Ari Beser's Goss Grove Films - of these devastating minutes and their aftermath.

Hibakusha like Yoshie Oka have been at the front of the fight to ban and eliminate nuclear weapons for decades, pledging to make sure that nobody else would have to go through the horrors they witnessed on that day. Today, we are closer than ever to achieving their goal, through the UN Treaty on the Prohibition of Nuclear Weapons. Stand with the Hibakusha:

Video: Ari Beser's Goss Grove Films