Prison hulks were decommissioned ships that authorities used as floating prisons in the 18th and 19th centuries. They were extensively used in England. The notorious hulks played a crucial role in detaining criminals. The term "prison hulk" is not synonymous with the related term convict ship. A hulk is a ship that is afloat, but incapable of going to sea, whereas convict ships are seaworthy vessels that transport convicted felons from their place of conviction to their place of banishment.