His fortune came not from the cotton gin, but from mass-producing muskets with interchangeable parts. That technology played a big part in who won the Civil War. Source: National Archives ...

In 1798 he figured out how to manufacture muskets by machine so that the parts were interchangeable. It was as a manufacturer of muskets that Whitney finally became rich.

Eventually a contract for 10,000 muskets was given to Eli Whitney (yes, that Eli Whitney) on the strength of his demonstration of interchangeable parts. But Whitney would be many years late on his ...