The "North Carolina" class incorporated "all or nothing" armor which weighed 41% of the total displacement; it consisted of an "armored raft" that extended from just forward of the first gun turret to just aft of the rear gun turret. They had a main armored belt that was thick amidships, inclined at 15°, and backed by Special Treatment Steel (STS). This tapered down to on the lower edge of the belt. The ships had three armored decks; their main deck was thick, the second, thickest deck was of armor laminated on STS for a total of , and the third and thinnest deck was thick. The first deck was designed to cause delay-fuzed projectiles to detonate, while the thicker second deck would protect the ships' internals. The third deck was intended to protect against shell splinters that might have penetrated the second deck; it also acted as the upper support for the torpedo bulkheads. The conning tower was connected to the armored citadel by a thick communications tube. Armor thickness for the conning tower itself ranged from on both sides to on the front and rear. The roof was thick and the bottom was thick.