Letter from Robert Brennan to Joseph P. Walshe (Dublin)

The following account of Hiroshima was given to me (and a few others) by an American officer who visited the place some time after the explosion.

The centre of the city for three miles was flattened out and nothing was left but a sea of cinders and ashes. The shells of a few concrete buildings still stood. The bomb released a heat of two million degrees Fahrenheit. The air rushing in to fill the vacuum thus created caused a wind which levelled houses and trees in its path. It was this air converging on the centre of the explosion and rushing upward which caused the huge giant mushroom-like vapour formation which in an incredibly short time reached a height of 40,000 feet. Trees far from the centre of the explosion were seared yellow. There were upwards to 50,000 people killed outright of whom 25,000 were children on their way to school. The succeeding death rate was about 500 a day. The weight of the explosive in the bomb is 40 ounces though the whole contrivance weighs 50 to 100 lbs. and is shaped like a gate post. The final explosion is caused by bringing together two substances by means of a chain of explosions. Before the bomb struck there had been an alert sounded in the city but the all clear signal was given in the mistaken impression that the airplane had gone away. Actually at an immense height it had shut off its engines and was circling into position to release the bomb by parachute. Hiroshima was a vulnerable target for the bomb because the city was in the shape of a bowl on either side of a river. Nagasaki was not so bad because there was a hill which protected a major section of the town.