Editing Montana-class battleship (section)

===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}}