Montana-class battleship
The Montana-class was a planned class of battleship for the United States Navy, intended as the successor to the. They were to be slower but larger, better armored, and with superior firepower. Five were approved for construction during World War II, but changes in wartime building priorities resulted in their cancellation in favor of continuing production of s and Iowa-class battleships before any Montana-class keels were laid.
Armament would have been twelve Mark 7 guns in four 3-gun turrets, up from the nine Mark 7 guns in three turrets used by the Iowa class. Unlike the three preceding classes of battleships, the Montana class was designed without any restrictions from treaty limitations. With increased anti-aircraft capability and substantially thicker armor in all areas, the Montanas would have been the largest, best-protected, and most heavily armed US battleships ever, and the only ones to rival Japan's s in terms of displacement.
Preliminary design work for the Montana class began before the US entry into World War II. The first two vessels were approved by Congress in 1939 following the passage of the Naval Act of 1938. The Japanese attack on Pearl Harbor delayed the construction of the Montana-class. The success of carrier combat at the Battle of the Coral Sea and, to a greater extent, the Battle of Midway, diminished the perceived value of the battleship. Consequently, the US Navy chose to cancel the Montana-class in favor of more urgently needed aircraft carriers as well as amphibious and anti-submarine vessels.
Background
During the interwar period, the US Navy was primarily concerned with its rival in the Pacific Ocean, the Imperial Japanese Navy. The international naval arms limitation system initiated by the Washington Naval Treaty in 1922 had accorded the US Navy superiority over Japan in terms of total tonnage. After the ten-year construction moratorium that had been imposed by the Washington Treaty expired, the US Navy began building the fast battleships in 1937 to replace old pre-World War I ships that were by then obsolescent. But by the late 1930s, the Washington system, which had been extended by the First and Second London Naval Treaties, had begun to break down after Japan refused to sign the Second London Treaty in 1936. This prompted the other major naval powers to begin rearmament programs, beginning in the United States with the battleships in 1938. Funding for the first two new ships was provided in Fiscal Year 1937, though work would not commence until 1939.The Second Vinson Act of 1938 added two more South Dakotas; it also authorized the construction of two more battleships yet to be designed. The US Navy had already begun design work on the successors to the South Dakotas in 1937, which was to become the ; the Navy sought larger, faster ships that would handily exceed the limit on battleship displacement imposed under the Washington Treaty system. Because Japan had already refused to abide by the terms of the Second London Naval Treaty, the other major naval powers moved to loosen the restrictions on their own new battleship designs. On 31 March 1938, the US, Britain, and France exchanged notes indicating that they would accept increasing the displacement limit to.
As the US Navy's designers worked on proposals for the new ships, two distinct strains emerged: a comparatively slow, heavily armed and armored variant and a much faster, but lighter-armed and armored vessel that was primarily intended to catch Japanese cruisers and counter the fast s. The latter type, which eventually emerged essentially as an improved South Dakota, was capable of a speed of, but work on the former proceeded at the same time. The General Board intended it to become the next generation of standard-type battleships, which was to be set at 45,000-ton ships armed with twelve guns, and capable of, the same speed as the South Dakotas.
By 1939, it had become apparent to the naval leadership that war was approaching, and so the need for new ships had become pressing. The start of World War II in Europe, and particularly the Fall of France in June 1940 only increased the pressure to speed construction of new warships. The first two ships ordered to the 33-knot improved South Dakota design— and —were ordered under the 1939 fiscal year. The passage of the Two-Ocean Navy Act on 19 July 1940 provided significant increases to the Navy's strength, including an increase of some for battleships alone, along with hundreds of thousands of tons for new aircraft carriers, cruisers, and destroyers. Under the 1941 fiscal year program, the third and fourth Iowa-class battleships were authorized, but in May, two more ships were added to the program. These were to have been built to the next battleship design, but the Secretary of the Navy, Frank Knox, decided that these should be additional Iowa-class ships to speed up production.
Design
Initial design work
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 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 that conformed to the 45,000-ton limit, armed with twelve 16-inch guns, and capable of 27-knots.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, and the ship was only protected against the earlier AP shell. The design staff estimated that more than would be needed to protect the ship against the heavier shells. A second variant, "BB 65B" substituted twelve new /47 guns in place of the existing twenty /38 cal guns for their 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 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 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.
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 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 Dakotas. One proposal, "65J", suggested adopting a twelve-gun ship that would be well-protected against the 2,700 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.
Wartime designs
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 docks. The Navy had been pushing for a third, wider set of locks for the Panama Canal since 1938, which was approved in 1940. 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 New York Navy Yard slipways could not handle the construction of a ship more than, 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. 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. 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. An option to replace the standard 5-inch/38 secondaries with longer-barrel 5-inch/54 guns would add about to the ships.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, 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. 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.
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, and capable of 28 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 numbers had been assigned to the Iowa class, the next design was labeled "BB 67-1". This design shortened the hull to at the waterline, likely to keep the length within the limits of the new slipways being built at the Norfolk Navy Yard and the Philadelphia Navy Yard. This variant displacement increased to. Further iterative improvements of the armor layout produced "BB 67-2", which had a slightly reduced displacement of. This version incorporated an internal lower belt that provided additional protection against underwater shell hits.
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 guns with Bofors guns. The searchlights were rearranged, the navigational rangefinders were removed, and the waterline hull length was increased slightly to. Displacement was increased slightly, to, while the designers discovered that the propulsion system could be reduced in power, from, which allowed smaller and lighter propulsion machinery. These changes provided further savings in weight that allowed the bomb 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 ; their resistance to standard 16-inch AP shells extended to. The final version of the design, dated March 1941, was designated "BB 67-4".