He built the first steam-powered locomotive in the United States for use on the B&O in 1830. Working in the Mt. Clare Shops, he fashioned a small engine made of borrowed wheels, scrap iron, and a tiny vertical boiler with musket barrels for boiler tubes. The “Tom Thumb” was capable of speeds of 12 to 14 miles per hour. Cooper’s engine carried the B&O directors on a 13 mile excursion to Ellicott’s Mills in just fifty-seven minutes. It was on a return trip from the same destination that the engine lost a race with a gray mare. Despite the loss due to a mechanical problem, the performance of the “Tom Thumb” convinced B&O leaders that steam locomotives were the future power source for its trains.