The Scharnhorst-class ships were equipped with Krupp armor.
Their upper armored deck was 50 mm (2.0 in) thick, and backed by the main armor deck.
This deck was 20 mm (0.79 in) 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 105 mm (4.1 in) 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 350 mm (14 in) 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 150 mm (5.9 in), which tapered down to zero at the bow of the ship.
Aft of the rear gun turret the belt decreased to 200 mm (7.9 in), and eventually tapered down to nothing at the stern.
The central portion of the belt was backed by 170 mm (6.7 in) thick shields.
The belt armor was composed of Krupp Cemented steel (KC).
The side protection system could not be penetrated by a 2,240 lb (1,020 kg) 16 in (406 mm) shell at any range over 11,000 m (12,000 yd).

The forward conning tower had 350 mm-thick sides and a roof that was 200 mm-thick.
The rear conning tower was less well armored, with sides and a roof that were only 100 mm (3.9 in) and 50 mm thick, respectively.
The gun turrets for the main battery had 360 mm (14 in) thick faces, 200 mm thick sides, and 150 mm thick roofs.
The barbettes that held the 28 cm gun turrets were also heavily armored; the sides were 350 mm thick and tapered down to 200 mm on the centerline, where they were shielded by the gun turrets above.
The faces of the 15 cm turrets were 140 mm (5.5 in) thick, with 60 mm (2.4 in) thick sides and 50 mm thick roofs.
The 10.5 cm gun mounts were equipped with 20 mm (0.79 in) gun shields.
All of this armor was KC steel.

The underwater protection system was designed to withstand a direct hit from a 250 kg (550 lb) explosive warhead; British aerial torpedoes had smaller warheads than this, but their ship-launched weapons were more powerful.
The navy conducted several full-scale underwater explosion tests with sections of armor cut from the old pre-dreadnought Preussen.
The tests revealed that welded steel construction better withstood the impact of the 250 kg warhead than did riveted steel plates.
The torpedo bulkhead, composed of Wotan Weich (Wotan, soft) steel, placed behind the armored belt was riveted; this was done because plate joints that had been incorrectly welded would not sufficiently withstand explosive shocks.
The underwater protection system was constructed out of several layers: the outer layer that was between 12–66 mm (.47–2.6 in) thick, directly underneath the main armored belt, was designed to detonate the torpedo warhead.
Behind the outer plate was a large void which would allow gases from the explosion to expand and dissipate.
Beyond this was a fuel bunker with an 8 mm (0.31 in) thick outer wall; this would absorb any remaining explosive force.
The bunker was supported by longitudinal stiffeners and transverse bulkheads.

The underwater side protection had numerous faults.
It was extremely strong amidships, but weakened on either end of the citadel.
The underwater protection could only stop a 200 kg (440 lb) warhead in these areas.
Another significant weakness in the design was the arrangement of the torpedo bulkhead.
It was connected to the lower portion of the sloped deck, at an angle of 10°; two riveted angled bars held it in place.
The bars were constantly under a great deal of stress, due to normal bending forces in the hu
The Scharnhorst-class ships were equipped with Krupp armor. Their upper armored deck was 50 mm (2.0 in) thick, and backed by the main armor deck. This deck was 20 mm (0.79 in) 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 105 mm (4.1 in) 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 350 mm (14 in) 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 150 mm (5.9 in), which tapered down to zero at the bow of the ship. Aft of the rear gun turret the belt decreased to 200 mm (7.9 in), and eventually tapered down to nothing at the stern. The central portion of the belt was backed by 170 mm (6.7 in) thick shields. The belt armor was composed of Krupp Cemented steel (KC). The side protection system could not be penetrated by a 2,240 lb (1,020 kg) 16 in (406 mm) shell at any range over 11,000 m (12,000 yd).
The forward conning tower had 350 mm-thick sides and a roof that was 200 mm-thick. The rear conning tower was less well armored, with sides and a roof that were only 100 mm (3.9 in) and 50 mm thick, respectively. The gun turrets for the main battery had 360 mm (14 in) thick faces, 200 mm thick sides, and 150 mm thick roofs. The barbettes that held the 28 cm gun turrets were also heavily armored; the sides were 350 mm thick and tapered down to 200 mm on the centerline, where they were shielded by the gun turrets above. The faces of the 15 cm turrets were 140 mm (5.5 in) thick, with 60 mm (2.4 in) thick sides and 50 mm thick roofs. The 10.5 cm gun mounts were equipped with 20 mm (0.79 in) gun shields. All of this armor was KC steel.
The underwater protection system was designed to withstand a direct hit from a 250 kg (550 lb) explosive warhead; British aerial torpedoes had smaller warheads than this, but their ship-launched weapons were more powerful. The navy conducted several full-scale underwater explosion tests with sections of armor cut from the old pre-dreadnought Preussen. The tests revealed that welded steel construction better withstood the impact of the 250 kg warhead than did riveted steel plates. The torpedo bulkhead, composed of Wotan Weich (Wotan, soft) steel, placed behind the armored belt was riveted; this was done because plate joints that had been incorrectly welded would not sufficiently withstand explosive shocks. The underwater protection system was constructed out of several layers: the outer layer that was between 12–66 mm (.47–2.6 in) thick, directly underneath the main armored belt, was designed to detonate the torpedo warhead. Behind the outer plate was a large void which would allow gases from the explosion to expand and dissipate. Beyond this was a fuel bunker with an 8 mm (0.31 in) thick outer wall; this would absorb any remaining explosive force. The bunker was supported by longitudinal stiffeners and transverse bulkheads.
The underwater side protection had numerous faults. It was extremely strong amidships, but weakened on either end of the citadel. The underwater protection could only stop a 200 kg (440 lb) warhead in these areas. Another significant weakness in the design was the arrangement of the torpedo bulkhead. It was connected to the lower portion of the sloped deck, at an angle of 10°; two riveted angled bars held it in place. The bars were constantly under a great deal of stress, due to normal bending forces in the hu
Scharnhorst-class battleship