philosophy, with most of the armor concentrated on the citadel that includes the machinery spaces, armament, magazines, and command and control facilities. Unlike the previous Iowa and South Dakota classes, the Montana class design returned to an external armor belt due to the greater beam providing sufficient stability while having the required belt inclination; this arrangement would have made construction and damage repairs much easier. The belt armor would be Class A face-hardened Krupp cemented (K.C.) armor mounted on Special Treatment Steel (STS), inclined at 19 degrees. Below the waterline, the belt tapered to . To protect against potential underwater shell hits, the ships would have a separate Class B homogeneous Krupp-type armor lower belt, by the magazines and by the machinery, that would also have served as one of the torpedo bulkheads, inclined at 10 degrees; this lower belt would taper to 1 inch at the triple bottom and be mounted on STS. The ends of the armored citadel would be closed by Class A traverse bulkheads thick in the front and in the aft. The deck armor would be in three layers: the first consisting of STS laminated on STS for a total of STS weather deck, the second consisting of Class B laminated on STS for a total of , and a third splinter deck. Over the magazines, the splinter deck would be replaced by a STS third deck to protect from spalling. Total armor thickness on the centerline would therefore have been 9.925 in (252 mm) over the citadel and 10.3 in (262 mm) thick over the magazines. The outboard section would have had Class B laminated on STS for a total of second deck and a splinter deck. The total thickness for the outboard section of the deck would have been 8.1 in (206 mm). The main batteries were designed to have very heavy protection, with turret faces having Class B mounted on STS, resulting in thick laminated plate. The turret sides were to have up to Class A and turret roofs would have Class B. The barbettes would have been protected by up to Class A forward and aft, while the conning tower sides would have Class A. Montanas torpedo protection system design incorporated lessons learned from those of previous US fast battleships, and was to consist of four internal longitudinal torpedo bulkheads behind the outer hull shell plating that would form a multi-layered