Editing Montana-class battleship (section)

== Design ==
===Initial design work===
[[File:Battleship Study - BB65 - Scheme 4 - (1940 Studies).jpg|thumb|left|1940 study plan, BB-65 Scheme 4 (BB 65-4)]]

Though the 33-knot design had been chosen for ''Iowa'', it was clear to naval leadership that these would be exceptions to normal Navy doctrine, and that a reversion to the 27-knot standard-type battleship would occur with the next design. The primary consideration for this new class was the development of the super-heavy {{convert|2700|lb|adj=on}} [[Armour-piercing ammunition|armor-piercing shell]] that had been developed during the construction of the ''North Carolina'' class. Standard design practice stated that battleships should be immune to guns of their own calibers at expected battle ranges, but the new super-heavy shell had significantly better penetrating power than older, lighter shells. None of the existing designs, from ''North Carolina'' to ''Iowa'', were proof against the 2,700-pound shell, and the General Board wanted the next design to be better protected. They requested proposals from the [[Bureau of Construction and Repair]] (C&R) that conformed to the 45,000-ton limit, armed with twelve 16-inch guns, and capable of 27-knots.{{sfn|Friedman|1985|p=329}}

C&R initially responded with a design labeled "BB 65A", which used ''South Dakota'' as a baseline, but increased the length to accommodate the fourth main battery turret. Displacement was already over the limit at {{cvt|45435|LT}}, and the ship was only protected against the earlier {{cvt|2250|lb}} AP shell. The design staff estimated that more than {{cvt|2000|LT|0}} would be needed to protect the ship against the heavier shells. A second variant, "BB 65B" substituted twelve new {{cvt|6|in|0}} /47 guns in place of the existing twenty [[5"/38 caliber gun|{{cvt|5|in|0}}/38 cal guns]] for their [[secondary armament|secondary batteries]], but this increased displacement even further. Another pair of designs, "BB 65C" and "65D", adopted three quadruple main battery turrets instead of four triple turrets, which accounted for some {{cvt|1600|LT|0}} of weight savings. This latter pair mirrored the first set in the use of 5-inch and 6-inch secondaries. All of these designs were only protected against the 2,250&nbsp;lb shell, but since "C" and "D" were below the displacement limit, C&R attempted to use the free weight to strengthen their armor with design "BB 65E". They realized that though the deck could be improved to provide a relatively narrow [[zone of immunity]] against [[plunging fire]], strengthening the [[belt armor]] to protect against the heavier shell would increase displacement to as much as {{cvt|55000|LT}}.{{sfn|Friedman|1985|p=329}}

None of the initial proposals was deemed acceptable, and there were concerns about the feasibility of the quadruple turrets. Other guns were suggested, ranging from {{cvt|18|in|0}} guns to experimental 16-inch/56 caliber guns. C&R provided another series of studies beginning with "65F". Several of these proposals experimented with mixed quadruple, triple, and double turrets for either ten or eleven guns to save weight but still increase firepower over the nine-gun ''South Dakota''s. One proposal, "65J", suggested adopting a twelve-gun {{cvt|14|in|0}} ship that would be well-protected against the 2,700&nbsp;lb AP shell. The 18-inch gun was ruled out after a design study demonstrated that only six of the guns could be mounted within the 45,000-ton displacement limit. By September 1939, one of the ten-gun variants had been selected, which carried two triple-turrets forward and a quadruple turret aft.{{sfn|Friedman|1985|pp=329–332}}

===Wartime designs===
[[File: Battleship Study - BB65 - Scheme 8 - (1940 Studies).jpg|thumb|right|One variant of the fast BB 65-8 design scheme from 1940]]

The outbreak of World War II in September 1939 radically altered the constraints imposed on C&R. The remaining limits imposed by the Washington and London treaties were now removed entirely; the new ship would only be limited by logistical restrictions of existing naval infrastructure, most significantly the [[Panama Canal]] and available [[dry dock]]s. The Navy had been pushing for a third, wider set of locks for the Panama Canal since 1938, which was approved in 1940.{{sfn|Friedman|1985|p=332}} Nevertheless, some limitations still existed; the length and height of the BB65 designs had to take into account one of the shipyards at which they were to be built: the [[Brooklyn Navy Yard|New York Navy Yard]] slipways could not handle the construction of a ship more than {{convert|58000|LT|}}, and vessels built there had to be low enough to clear the [[Brooklyn Bridge]] at [[low tide]]. Consequently, the yard's number 4 dry dock had to be enlarged and the ships would be floated out rather than conventionally launched.{{sfn|Garzke|Dulin|1995|p=162}} In October, the General Board asked for new twelve-gun designs that were sufficiently armored, which was estimated could be accomplished on a displacement of around {{cvt|50000|LT}}. The Preliminary Design department at C&R responded with a design in mid-January 1940 that largely met the General Board's requirements, but displacement was set at {{cvt|51500|LT}}. An option to replace the standard 5-inch/38 secondaries with longer-barrel [[5"/54 caliber Mark 16 gun|5-inch/54 guns]] would add about {{cvt|2000|LT|0}} to the ships.{{sfn|Friedman|1985|p=332}}

During a meeting on 16 February 1940, the Board requested a new series of proposals. These included a modified version of the nine-gun ''Iowa'' design that was two knots slower but better protected, an enlarged ''Iowa'' variant that maintained the 33-knot speed but displaced {{cvt|53500|LT}}, and several twelve-gun designs that had speeds ranging from 28 to 33 knots. These were given designations from "BB 65-1" to "BB 65-8". Displacement on these proposals increased to as much as {{cvt|67000|LT}}. All of these designs were armed with the 16-inch/50 gun, and were well protected against the super-heavy shell. During discussions in March, the decision was made to revert to externally applied belt armor, since the internal armor belts of the ''South Dakota'' and ''Iowa'' classes were more difficult to install and repair in the event of battle damage, and the weight savings associated with them no longer mattered now that displacement limits were gone. Two additional designs were produced in June: 65-9 and 65-10, which were 28-knot ships.{{sfn|Friedman|1985|pp=333–335}}{{sfn|Garzke|Dulin|1995|p=158}}

By July, Navy's senior leadership still could not agree on design priorities, and disagreed sharply on points ranging from top speed to the cost and logistical challenges of the larger designs. The Board requested another round of design studies from Preliminary Design, which responded with nine-, ten-, and twelve-gun ships that, again, included slow and fast variants. The Board finally selected one of the designs, "BB 65-5A", which was armed with twelve guns on a displacement of {{cvt|57500|LT}}, and capable of 28&nbsp;knots. The Board submitted the design to Knox, which he approved on 19 August. The ships were not actually authorized at that point, and design work continued. Because the battleships that would have received the BB-65 and BB-66 [[hull number]]s had been assigned to the ''Iowa'' class, the next design was labeled "BB 67-1". This design shortened the hull to {{cvt|880|ft}} at the waterline, likely to keep the length within the limits of the new [[slipway]]s being built at the [[Norfolk Navy Yard]] and the [[Philadelphia Navy Yard]]. This variant displacement increased to {{cvt|61200|LT}}. Further iterative improvements of the armor layout produced "BB 67-2", which had a slightly reduced displacement of {{cvt|59700|LT}}. This version incorporated an internal lower belt that provided additional protection against underwater shell hits.{{sfn|Garzke|Dulin|1995|p=158}}{{sfn|Friedman|1985|pp=336–337}}

Detail work on the design continued well into 1941, which included replacing the original battery of light anti-aircraft guns, which were to be the ineffective {{cvt|1.1|in}} guns with [[Bofors 40 mm L/60 gun|Bofors {{cvt|40|mm}} guns]]. The [[searchlight]]s were rearranged, the navigational [[rangefinder]]s were removed, and the waterline hull length was increased slightly to {{cvt|890|ft}}. Displacement was increased slightly, to {{cvt|60500|LT}}, while the designers discovered that the propulsion system could be reduced in power, from {{convert|212000|to|172000|shp|lk=on}}, which allowed smaller and lighter propulsion machinery. These changes provided further savings in weight that allowed the bomb [[deck (ship)|deck]] to be extended further aft, and improvements to the light anti-aircraft battery. Protection of the propulsion shafts also changed from an extension of the belt and main armored deck aft of the citadel to armored tubes around the shafts, with the steering gears becoming its own armored compartment. This design was immune to the super-heavy shells when fired at ranges between {{convert|18000|and|31000|yd|m}}; their resistance to standard 16-inch AP shells extended to {{convert|16500|and|34500|yd|m}}. The final version of the design, dated March 1941, was designated "BB 67-4".{{sfn|Friedman|1985|pp=338–342}}{{sfn|Garzke|Dulin|1995|pp=163–164, 170, 173}}