Pensacola-class cruiser

The Pensacola class was a class of United States Navy heavy cruiser, the first "treaty cruisers" designed under the limitations set by the Washington Naval Treaty, which limited cruisers to a maximum of 10000 LT displacement and a maximum main battery caliber of 8 in.

Description
In an effort to remain within treaty limits, while still mounting a very heavy main battery of ten 8 in guns, the hull was of welded construction, and the armor belt was thin (varying from 2.5 to 4 in in thickness). This was inadequate to protect her vitals from enemy 8-inch shells and was no thicker than the armor on 6 in gun cruisers. In fact, USS Pensacola (CA-24) and USS Salt Lake City (CA-25) were classified as light cruisers due to their minimal armor, until re-designated in July 1931 as heavy cruisers in accord with international practice of designating all cruisers with guns larger than 6-inch as heavy cruisers.

Their main armament consisted of ten 8-inch guns, in two twin turrets on the main deck, and two triple turrets two decks above, making it one of the two US Navy ship classes (besides the Nevada-class battleships) to have different-sized turrets for main armament. All the guns in each turret were mounted in a single slide, and were unable to elevate independently of one another. Also, unlike the very few other ships with different-sized main battery turrets (Nevada-class battleships and King George V-class battleships) the Pensacolas had the larger turrets superfiring over the smaller turrets, whereas the others had the larger turrets on "bottom". Placing heavier turrets above lighter ones allows for finer lines for a given length, however causing topheaviness and reducing stability.

Unfortunately, because of the rather unusual main battery layout and their heavy tripod fore-masts, they were top-heavy and prone to excessive rolling. This combined with low freeboard forward made them inferior seaboats compared to later designs. Rework in the shipyards modified the hull and superstructure in the 1930s to eliminate the rolling.

The Navy built only two ships in this class before switching to the Northampton-class cruiser design. Many of the deficiencies of the Pensacolas were corrected by reducing the main battery to three triple turrets (two forward, one aft) and adding another upper deck forward of amidships.