The City class, also known as the Cairo Class, of riverine ironclads was a series of purpose built river gunboats built to one standard design under the direction of James Eads with assistance from Samuel Pook . Despite the figures given for them in most sources, it is rarely noted that these were, in fact, only partially ironclad vessels. They were the engine that drove much of the Union's river campaign forward, particularly in the 1861-1862 period, and some actually saw service before Monitor had her famous duel at Hampton Roads. During the period, the ships were often referred to as "Pook Turtles" or "Pook Rams" unofficially because of their appearance.
Although protected by reinforced layers of wood, actual iron plating covered only the pilothouse, the forward facing of the casemate, and sections of the casemate stretching from amidships to the engine area. Armored plates were also installed around the gunports. As the war went on, this armor protection was found to be inadequate, and in many cases local modifications were made to individual members of the class, including the attachment of additional armor plate and the sandbagging of open areas of deck.
The City Class saw heavy service throughout the war, with two of the ships - Cairo and St. Louis , lost to mines, and several others sunk multiple times in shallow water by Confederate gunfire and/or ramming attacks. Many of the class suffered from quite significant damage, particularly due to their inadequate armor protection. They were particularly vulnerable to plunging fire from well sited Confederate guns. Against other ironclads, they had a very poor record - most of the time being outgunned and outmaneuvered, as with the case of CSS Arkansas and the USS Carandolet .
Nevertheless, it is a testament to the basic soundness of their design and engineering that most vessels of the fleet were raised and repaired multiple times.