 The design team envisioned the H-class ships fighting at relatively close range, and therefore selected the armor system that had been used by German battleship constructors since the Nassau class of 1907. The side belt was vertical and was attached directly to the side of the hull, in contrast with the inclined armor belt placed inboard of the side wall used by American and French designers. The side belt, which consisted of Krupp cemented steel armor (KCA), was 300 mm (12 in) thick in the central section that covered the ammunition magazines and machinery spaces. The belt was reduced to 220 mm (8.7 in) on either end of the main section; the stern and bow were unprotected by the main belt. The upper side belt was 145 mm (5.7 in) thick. The German navy did not preserve official estimates for the immunity zone, though Garzke and Dulin created an estimate based on the performance of the US 16 in (41 cm) 45 caliber gun firing a 1,016 kg (2,240 lb) shell. The ships' main armor would have rendered them proof against the 16 in shell at ranges between 11,000 to 21,000 m (36,000 to 69,000 ft). The 16 in shell could penetrate the upper side belt at any range, however, which left the ships exposed above the waterline.
