Editing Montana-class battleship (section)

=== Armor ===
[[File:USS Montana (BB-67) Stern.jpg|thumb|right|Stern view of a ''Montana''-class battleship model]]

As designed, the ''Montana''s used the [[All or nothing (armour)|"all or nothing"]] armor philosophy, with most of the armor concentrated on the citadel that includes the machinery spaces, armament, magazines, and command and control facilities. The belt armor would be {{cvt|16.1|in|0}} Class A face-hardened [[Krupp armor|Krupp cemented]] (K.C.) armor mounted on {{cvt|1|in}} [[Special Treatment Steel]] (STS), inclined at 19 degrees. Below the waterline, the belt tapered to {{cvt|10.2|in|0}}. To protect against potential underwater shell hits, the ships would have a separate Class B homogeneous Krupp-type armor lower belt, {{cvt|8.5|in|0}} by the magazines and {{cvt|7.2|in|0}} by the machinery, that would also have served as one of the [[torpedo bulkhead]]s, inclined at 10 degrees; this lower belt would taper to 1 inch at the triple bottom and be mounted on {{cvt|0.75|in}} STS. The ends of the armored citadel would be closed by Class A traverse bulkheads {{cvt|18|in|0}} thick in the front and {{cvt|15.25|in}} in the aft.{{sfn|Garzke|Dulin|1995|p=173}}

The deck armor would be in three layers: the first consisting of {{cvt|0.75|in}} STS laminated on {{cvt|1.5|in}} STS for a total of {{cvt|2.25|in}} STS weather deck, the second consisting of {{cvt|5.8|in|0}} Class B laminated on {{cvt|1.25|in|0}} STS for a total of {{cvt|7.05|in|0}}, and a third {{cvt|0.625|in|0}} splinter deck. Over the magazines, the splinter deck would be replaced by a {{cvt|1|in}} STS third deck to protect from spalling. Total armor thickness on the centerline would therefore have been 9.925 in (252&nbsp;mm) over the citadel and 10.3 in (262&nbsp;mm) thick over the magazines. The outboard section would have had {{cvt|6.1|in|0}} Class B laminated on {{cvt|1.25|in|0}} STS for a total of {{cvt|7.35|in|0}} second deck and a {{cvt|0.75|in}} splinter deck. The total thickness for the outboard section of the deck would have been 8.1 in (206&nbsp;mm).{{sfn|Garzke|Dulin|1995|p=173}}

The main batteries were designed to have very heavy protection, with turret faces having {{cvt|18|in|0}} Class B mounted on {{cvt|4.5|in|0}} STS, resulting in {{cvt|22.5|in|0}} thick laminated plate. The turret sides were to have up to {{cvt|10|in|0}} Class A and turret roofs would have {{cvt|9.15|in|0}} Class B. The barbettes would have been protected by up to {{cvt|21.3|in|0}} Class A forward and {{cvt|18|in|0}} aft, while the [[conning tower]] sides would have {{cvt|18|in|0}} Class A.{{sfn|Garzke|Dulin|1995|pp=173–174}}

''Montana''{{'}}s 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 "bulge". Two of the compartments would be liquid loaded in order to disrupt the gas bubble of a torpedo warhead detonation while the bulkheads would elastically deform and absorb the energy. Due to the external armor belt, the geometry of the "bulge" was more similar to that of the ''North Carolina'' class rather than that of the ''South Dakota'' and ''Iowa'' classes. The design of the ''Montana''{{'}}s torpedo defense system addressed a potential vulnerability of the ''South Dakota''-type system, where caisson tests in 1939 showed that extending the main armor belt that tapers to the keel to act as one of the torpedo bulkheads had detrimental flooding effects due to the belt's rigidity. ''South Dakota''{{'}}s and ''Iowa''{{'}}s systems were modified in light of these tests, and ''Iowa''{{'}}s system was also further reinforced.{{sfn|Jurens|Morss|2016|pp=289–294}} Like on the ''South Dakota'' and ''Iowa'' classes, the two outer compartments would be liquid loaded, while two inner ones be void with the lower Class B armor belt to form the holding bulkhead between them. The greater beam of the ''Montana''s would allow a higher system depth of {{cvt|20.5|ft|2}} compared to {{cvt|18.5|ft|2}} of the ''North Carolina''s.{{sfn|Garzke|Dulin|1995|pp=168–169}}