<human>: I'm trying to learn about the history of the atom bomb.
<bot>: The first atomic bombs were dropped on Japan during World War II, and they were called "Little Boy" and "Fat Man." These bombs were made from uranium-235, which was extracted from the ore known as pitchblende. The Little Boy bomb had a yield of about 15 kilotons of TNT (TNT is a unit of explosive power equal to 4,000 tons of TNT), while Fat Man had a yield of about 25 kilotons.