The main battery turrets were heavily armored: the turret faces were 16-inch thick, the sides were thick, the rear sides were thick, and the roofs were thick. Sixteen–inch-thick armor was the maximum width factories were able to produce at the time of the ships' design; by 1939, however, it was possible to create -thick plates. These were not installed because it was estimated that the conversion would delay completion of the ships by 6 to 8 months. The barbettes that held the turrets were also strongly protected. The front portion was , the sides increased to 16 in, and the rear portion reduced to . The 5-inch gun turrets, along with their ammunition magazines, were armored with STS plates.