The "Scharnhorst"-class ships were equipped with Krupp armor. Their upper armored deck was thick, and backed by the main armor deck. This deck was thick aft, increased to 50 mm in the central portion of the ship that contained the ammunition magazines and machinery spaces, and decreased down to 20 mm in the bow. It was supported by thick slopes on either longitudinal side. The slopes connected to the lower edge of the main belt, an arrangement referred to as the "turtle deck." The slopes significantly increased armor protection in the critical areas of the ship. The ships' vitals were well armored against any caliber shell fired by battleships at the time at ranges where the shell would have to penetrate both the main belt and the sloping deck. At very long ranges, the deck armor could be easily penetrated by heavy-caliber shells. All of these sections were composed of "Wotan Hart" (Wotan Hard) steel. The armored belt was thick in the central portion of the ship, where the critical areas of the ship were located. Forward of the "A" turret the belt was reduced to , which tapered down to zero at the bow of the ship. Aft of the rear gun turret the belt decreased to , and eventually tapered down to nothing at the stern. The central portion of the belt was backed by thick shields. The belt armor was composed of Krupp Cemented steel (KC). The side protection system could not be penetrated by a 16 in (406 mm) shell at any range over .