The New Orleans class was the last series of US cruisers completed to the  limitations of the Washington Naval Treaty of 1922.
As completed, the single ship  Wichita class (and subsequent heavy cruisers) exceeded the 10,000-ton standard.

Design of these ships began in early 1929, based on the three preceding classes: The Pensacola, the Northampton and the Portland classes.
All of the cruisers of the New Orleans class were outwardly similar but the displacement among these ships varied by some 600 tons.
The Bureau of Construction and Repair authorized a contemporary 8-inch (203 mm) gun cruiser design of smaller size, but one which allocated considerably more tonnage towards protection.
The New Orleans class was noteworthy for its protection.
The hull was 12 feet (3.7 m) shorter than a Northampton, with a shorter armor belt that protected only the machinery and other internal spaces, allowing its thickness to be increased to 5 inches (130 mm).
The machinery bulkheads were given 3.5 inches (89 mm) and the deck armor was strengthened to 2.25 inches (57 mm).
For the first time in US cruisers, barbette and turret armor was sufficient to withstand 8-inch shellfire.
The turrets were faced with 8 inches of armor, 2.75 inches (70 mm) on the sides and 1 inch (25 mm) on the roof.
The barbettes were protected with 5 inches of armor on all ships except San Francisco, whose barbettes were fitted with 6.5 inches (170 mm) of armor.

Magazine protection was increased to 4 inches (100 mm).
Magazine protection was further increased by placing them well below the waterline.
 Otherwise only an internal splinter belt and the armor deck protected the magazines.
While this allowed an exceptional degree of armored protection for the vitals against shellfire, there was little protected hull volume, and the deep magazines were more exposed to underwater damage (New Orleans learned this the hard way at the Battle of Tassafaronga).
 Protection represented approximately 15% of normal displacement as opposed to the only 5.6% in the Pensacolas and 6% in the Northampton and Portland classes.
Unfortunately, fuel bunkerage had to be reduced, which resulted in a smaller operational range.
The New Orleans class was the last series of US cruisers completed to the  limitations of the Washington Naval Treaty of 1922. As completed, the single ship  Wichita class (and subsequent heavy cruisers) exceeded the 10,000-ton standard.
Design of these ships began in early 1929, based on the three preceding classes: The Pensacola, the Northampton and the Portland classes. All of the cruisers of the New Orleans class were outwardly similar but the displacement among these ships varied by some 600 tons. The Bureau of Construction and Repair authorized a contemporary 8-inch (203 mm) gun cruiser design of smaller size, but one which allocated considerably more tonnage towards protection. The New Orleans class was noteworthy for its protection. The hull was 12 feet (3.7 m) shorter than a Northampton, with a shorter armor belt that protected only the machinery and other internal spaces, allowing its thickness to be increased to 5 inches (130 mm). The machinery bulkheads were given 3.5 inches (89 mm) and the deck armor was strengthened to 2.25 inches (57 mm). For the first time in US cruisers, barbette and turret armor was sufficient to withstand 8-inch shellfire. The turrets were faced with 8 inches of armor, 2.75 inches (70 mm) on the sides and 1 inch (25 mm) on the roof. The barbettes were protected with 5 inches of armor on all ships except San Francisco, whose barbettes were fitted with 6.5 inches (170 mm) of armor.
Magazine protection was increased to 4 inches (100 mm). Magazine protection was further increased by placing them well below the waterline.  Otherwise only an internal splinter belt and the armor deck protected the magazines. While this allowed an exceptional degree of armored protection for the vitals against shellfire, there was little protected hull volume, and the deep magazines were more exposed to underwater damage (New Orleans learned this the hard way at the Battle of Tassafaronga).  Protection represented approximately 15% of normal displacement as opposed to the only 5.6% in the Pensacolas and 6% in the Northampton and Portland classes. Unfortunately, fuel bunkerage had to be reduced, which resulted in a smaller operational range.
New Orleans-class cruiser