Screw sloop

[2] If the term referred to a British warship, its meaning was heavily dependent on the number of officers and men on the vessel.

By this system, small frigates that lost most of their guns and sailors so they could be used as transports would be reclassified as sloops.

The same logic also applied to fireships, which were typically made by converting fifth- or sixth-rate ships.

[15] In the 1860s American context, the general meaning of the word 'sloop' was a three-masted square-rigged ship with a full broadside on a single deck.

In a looser sense, it could also refer to a three-masted vessel like CSS Alabama, which was a barque and lacked a full broadside.

[5] USS Princeton launched in September 1843, was the first world's screw steam vessel of war.

Princeton was also revolutionary because it had its engines under the waterline and had an armament that included a very high-caliber wrought-iron gun.

The success of Princeton led the United States Navy to slowly shift to the propeller as means of propulsion.