Abraham Lincoln was granted U.S. Patent No. 6,468 12 years before he became the 16th president.
The four-digit patent number is a telling indication of just how long ago that was.
The device was intended to help grounded steamboats get off shoals and sandbars without jettisoning heavy cargo; it involved inflatable chambers designed to float the ship off obstacles.
It was a promising idea, but was never tested or manufactured.
This is the only known patent held by a U.S. president.
