The main belt armor of this class was designed and tested to resist 381 mm armor-piercing shells at ranges down to , which was considered the inner edge of optimal combat range. The belt consists of a homogeneous armor outer plate and the cemented armor belt placed behind the outer plate; the 250 mm gap was filed with a cement foam called "Cellulite" to keep the water out of the gap and assist in de-capping armor piercing shells. The main armor belt was mounted on of oak timber and steel backing plate, and the entire belt structure was inclined at 11-15º, depending on the section of the hull. A homogeneous armor plate was placed behind the belt, followed behind by another plate sloped 26º in the opposite direction. The main citadel was closed off by forward and aft traverse bulkheads. The hull space above the citadel was an armored casemate with plating. The bow was protected by a belt that extends ahead of the main belt before terminating in a transverse bulkhead. The propeller shafts, aft diesel generator groups, and steering gear were protected by homogeneous armor plating and a separate bulkhead aft of the citadel.