On May 22, 1849, 12 years before he became the sixteenth U.S. president, Abraham Lincoln (1809–1865), was granted U.S. patent number 6,469 for a device to help steamboats pass over shoals and sandbars. The device, never tested or manufactured, had a set of adjustable buoyancy chambers (made from metal and waterproof cloth) attached to the ship’s sides below the waterline. Bellows could fill the chambers with air to float the vessel over the shoals and sand bars. It was the only patent ever held by a United States president.