"Little Boy" is the name given to the first atomic bomb used in combat. Its explosive power came from the radioactive element uranium-235. It was relatively simple, with a gun-like detonator. Little Boy was 120 inches long, 28 inches wide, and weighed about 8900 pounds.

Here's a picture of Little Boy before it was taken to combat.
Click here for a bigger picture.

Little Boy was dropped on the Japanese city of Hiroshima on August 6, 1945. It was carried by a B-29 bomber, piloted by United States Air Force Colonel Paul W. Tibbets. He christened the plane the night before the bombing, naming it Enola Gay, after his mother.
It took the bomb about one minute to reach the correct explosion altitude of about 1980 feet in the air. Little Boy exploded at 8:15 Japan Standard Time. It missed its target by around 600 feet. Little Boy exploded with a fifteen kiloton explosion.
Little Boy's explosive mechanism was relatively simple. Inside the bomb was a mass of uranium that was just less than the critical mass necessary to start the explosion. When detonated, a small piece of uranium--with just enough mass to combine with the larger amount and achieve critical mass--was "shot" into the larger piece, whereupon critical mass was achieved and the chain reaction that was the explosion was started. It was so simple and seemingly foolproof that there was not even a test of a similar bomb. Little Boy was the first of its type used.

Here's a picture of the explosion of Little Boy.

The explosion and cloud resulting from Little Boy were heard and seen by those near to and far away from the explosion, at least the ones who were not killed by it. Colonel Tibbets described it thus:
     
     "There was the mushroom growing up, and we watched it blossom. And down below it, the thing reminded me more of a boiling pot of tar than any other description I can give it. It was black and boiling underneath with a steam haze on top of it. And, of course, we had seen the city when we went in, and there was nothing to see when we came back. It was covered by this boiling, black-looking mess."--Col. Paul Tibbets

The Enola Gay deserves its own page, so here's the link to it.

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