The history of U.S.S. Cairo's armament can be traced to the second half of the 14th century when cannon were first carried aboard ships. These early cannon were most likely short weapons with bell-shaped mouths and probably did not have the benefit of carriages to hold them. The introduction of the gun port in 1501 meant heavier guns could be carried to sea, and in 1513, gunfire sank a ship for the first time. The construction of ships such as the Henry Grace a Dieu and the Sovereign of the Seas in the 16th and 17th centuries, respectively, signified the influence of cannon on ship design. The former vessel, also known as the Great Harry, was rebuilt in 1540 as a ship of 1,000 tons with a double tier of gun ports, while the latter vessel became the first three-decker on record carrying 102 guns. Naval warfare entered a new era when Henri-Joseph Paixhans invented the shell gun in 1822. For the first time, exploding shells could be fired from guns on a horizontal trajectory so that wooden ships were more likely to be sunk by an enemy vessel. Consequently, the ironclad was introduced in the mid-19th century and vessels like the U.S.S. Cairo would become the premier fighting machines of the Civil War.