Via The Black Inventor Online Museum:
Benjamin Bradley was born around 1830 as a slave in Maryland. He was able to read and write, although at the time it was illegal for a slave to do so (he likely learned from the Master's children). He was put to work in a printing office and at the age of 16 began working with scrap he found, modeling it into a small ship. Eventually, with an intuitiveness that seemed far beyond him, he improved on his creation until he had built a working steam engine, made from a piece of a gun-barrel, pewter, pieces of round steel and some nearby junk. Those around him were so astounded by his high level of intelligence that he was placed in a new job, this time at the United States Naval Academy in Annapolis, Maryland.
In his new position he served as a classroom assistant in the science department. He helped to set up and conduct experiments, working with chemical gases. He was very good at his work, impressing the professors with his understanding of the subject matter and also with his preparedness in readying the experiments. In addition to the praise he received, he also received a salary, most of which went to his Master, but some of which (about $5.00 per month) he was able to keep.
Despite enjoying his job with the Naval Academy, Bradley had not forgotten his steam engine creation. He used the money he had been able to save from his job as well as the proceeds of the sale of his original engine (to a Naval Academy student) to build a larger model. Eventually he was able to finish an engine large enough to drive the first steam-powered warship at 16 knots. At the time, because he was a slave, he was unable to secure a patent for his engine. His master did, however, allow him to sell the engine and he used that money to purchase his freedom.