 The original target for the bomb was the city of Kokura , but it was found to be obscured by clouds and drifting smoke from fires started by a major firebombing raid by 224 B @-@ 29s on nearby Yawata the previous day . This covered 70 % of the area over Kokura , obscuring the aiming point . Three bomb runs were made over the next 50 minutes , burning fuel and repeatedly exposing the aircraft to the heavy defenses of Yawata , but the bombardier was unable to drop visually . By the time of the third bomb run , Japanese anti @-@ aircraft fire was getting close , and Second Lieutenant Jacob Beser , who was monitoring Japanese communications , reported activity on the Japanese fighter direction radio bands . 
