Montana-class battleship
The Montana-class battleships were planned as successors of the for the United States Navy, 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.
Intended armament would have been twelve Mark 7 guns in four 3-gun turrets, up from the Iowas nine Mark 7 guns in three turrets. Unlike the three preceding classes of battleships, the Montana class was designed without any restrictions from treaty limitations. With an increased anti-aircraft capability and substantially thicker armor in all areas, the Montanas would have been the largest, best-protected, and most heavily armed U.S. battleships ever. They were also the only class to rival the Empire of Japan's immense s.
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 Second Vinson Act. The Japanese attack on Pearl Harbor delayed 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, amphibious and anti-submarine vessels.
Because the Iowas were far along enough in construction and urgently needed to operate alongside the new Essex-class aircraft carriers, their orders were retained, making them the last U.S. Navy battleships to be commissioned.
History
As the political situation in Europe and Asia worsened in the prelude to World War II, Carl Vinson, the chairman of the House Committee on Naval Affairs, instituted the Vinson Naval Plan, which aimed to get the Navy into fighting shape after the cutbacks imposed by the Great Depression and the two London Naval Treaties of the 1930s. As part of the overall plan, Congress passed the Second Vinson Act in 1938, which was promptly signed by President Franklin D. Roosevelt and cleared the way for construction of the four fast battleships and the first two fast battleships. Four additional battleships were approved for construction in 1940, with the last two intended to be the first ships of the Montana class. By 1942, it was apparent to the US Navy high command that they needed as many fast battleships as possible, and hull numbers BB-65 and BB-66 were allocated to planned Iowa-class fast battleships and.The Navy had been considering large battleship design schemes since 1938 to counter the threat posed by potential battleships of the Imperial Japanese Navy, which had refused to sign the Second London Naval Treaty and furthermore refused to provide details about its s. Although the Navy knew little about the Yamato class, some rumors regarding the new Japanese battleships placed main gun battery caliber at. The potential of naval treaty violations by the new Japanese battleships resulted in the remaining treaty powers, Britain, France and the United States, invoking the tonnage "Escalator Clause" of the Second London Naval Treaty in June 1938, which raised the maximum standard displacement limit from to.
The increased displacement limit allowed the Navy to begin evaluating 45,000-ton battleship designs, including "slow" schemes that increased firepower and protection over previous designs and also "fast" schemes. The "fast" design evolved into the Iowa class while the "slow" design, with main armament battery eventually settled on twelve guns and evolution into a 60,500-ton design, was assigned the name Montana and cleared for construction by the United States Congress under the Two-Ocean Navy Act in 1940; funding for the new ships was approved in 1941. These ships, the last battleships to be ordered by the Navy, were originally to be designated BB-65 through BB-69; however, BB-65 and BB-66 were subsequently re-ordered as Iowa-class ships, Illinois and Kentucky, and the Montanas were redesignated BB-67 through BB-71.
Completion of the Montana class, and the last two Iowa-class battleships, was intended to give the US Navy a considerable advantage over any other nation, or probable combination of nations, with a total of 17 new battleships by the late 1940s. The Montanas also would have been the only American ships to rival Japan's massive Yamato and her sister Musashi in size and raw firepower.
Design
Preliminary planning for the Montana-class battleships took place in 1939, when the aircraft carrier was still considered strategically less important than the battleship. The initial schemes for what would eventually become the Montana class were continuations of various 1938 design studies for a 45,000-ton "slow" battleship alternative to the "fast" battleship design that would become the Iowa class. The "slow" battleship design proposals had a maximum speed of and considered various main gun battery options, including /45 cal, 16-inch/50 cal, 16-inch/56 cal, and /48 cal guns; a main battery of twelve 16-inch/50 cal guns was eventually selected by the General Board for offering the best combination of performance and weight. The initial design schemes for the Montana class were given the "BB65" prefix.In July 1939, a series of 45,000-ton BB65 design schemes were evaluated, but in 1940, as a result of the outbreak of World War II and the abandonment of the naval treaties, the Battleship Design Advisory Board moved to larger designs capable of simultaneously offering increased armament and protection. The design board issued a basic outline for the Montana class that called for it to be free of beam restrictions imposed by the extant Panama Canal, be 25% stronger offensively and defensively than any other battleship completed or under construction, and be capable of withstanding the new "super heavy" armor-piercing shells used by US battleships equipped with either the 16-inch/45 cal guns or 16-inch/50 cal Mark 7 guns. No longer restricted by treaty displacement limits, naval architects were able to increase armor protection for the new BB65 design schemes, enabling the ships to withstand enemy fire equivalent to their own guns' ammunition. In conjunction with the Montana class, the Navy also planned to add a third set of locks to the Panama Canal that would be wide to enable ship designs with greater beam; these locks would have been armored and would normally be reserved for use by Navy warships. Although freed of the beam restriction from the extant Panama Canal, 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.
The larger BB65 design studies would again settle on main armament of twelve 16-inch/50 cal guns while providing protection against the "super heavy" AP shells. After debate at the design board about whether the Montana class should be fast, achieving the high speed of the Iowa class, or maintain the 27-to-28-knot speed of the North Carolina- and South Dakota classes, the lower speed was chosen in order to rein in size and displacement. Design study of the BB65-8 scheme for a 33-knot battleship resulted in standard displacement over, waterline length of, and required ; by returning the BB65 design to the slower maximum speed, the standard displacement and waterline length of the ships could be reduced to a more practical and respectively as exemplified by the BB65-5 scheme. In practice, the 27-to-28-knot speed would have still been enough to escort and defend the Pacific-based Allied fast aircraft carrier task forces, although the Montanas ability in this regard would be considerably more limited compared to the Iowas as the latter could keep up with fleet carriers at full speed. In September 1940, the 58,000-ton BB65-5A preliminary design scheme with powerplant, the same as the one on Iowa class, was refined and subsequently named BB67-1 after hull numbers BB-65 and 66 were reordered as Iowa-class ships Illinois and Kentucky. Waterline length was reduced from for BB65-5 to for BB65-5A and then increased to for BB67-1.
By January 1941, the design limit for the 58,000-ton battleship plan had been reached, and consensus among those designing the battleship class was to increase the displacement to a nominal to support the desired armor and weaponry on the ships. At the same time, upon discovering that the propulsion plant was more powerful than needed, planners decided to reduce output from 212,000 shaft horsepower in BB67-2 to in BB67-3 for a better machinery arrangement and improved internal subdivisions. The secondary armament battery of ten two-gun turrets was also changed to mount the /54 cal guns instead of the 5-inch/38 cal guns used on the Iowas. The number of 40-mm Bofors anti-aircraft gun mounts also increased, while protection of the propulsion shafts changed from the extension of the belt and deck armor aft of the citadel to armored tubes in an effort to control weight growth.
By 1942, the Montana class design was further revised to BB67-4. The armored freeboard was increased by, while the propulsion plant had its power reduced again to ; the standard displacement became and full load displacement was. Aesthetically, the net design for the Montana class somewhat resembled the Iowa class since they would be equipped with the same caliber main guns and similar secondary guns; however, Montana and her sisters would have more armor, mount three more main guns in one more turret, and be longer and wider than the Iowa class. The final contract design was issued in June 1942. Construction was authorized by the United States Congress and the projected date of completion was estimated to be somewhere between 1 July and 1 November 1945.
Fate
The Navy ordered the ships in May 1942, but the Montana class was placed on hold because the Iowa-class battleships and the Essex-class aircraft carriers were under construction in the shipyards intended to build the Montanas. Both the Iowa and Essex classes had been given higher priorities: the Iowas as they were far along enough in construction and urgently needed to operate alongside the Essex-class carriers and defend them with 5-inch, 40 mm, and 20 mm AA guns, and the Essexes because of their ability to launch aircraft to gain and maintain air supremacy over the islands in the Pacific and intercept warships of the Imperial Japanese Navy. The entire Montana class was suspended in June 1942 following the Battle of Midway, before any of their keels had been laid. In July 1943, the construction of the Montana class was finally canceled after the Navy fully accepted the shift in naval warfare from surface engagements to air supremacy and from battleships to aircraft carriers. Work on the new locks for the Panama Canal also ceased in 1941 owing to a shortage of steel due to the changing strategic and material priorities.Specifications
General characteristics
The final BB67-4 design for the Montana-class battleships was long at the waterline and long overall. The maximum beam was while the waterline beam was due to the inclination of the external armor belt. The design displacement figures were standard, full load, and emergency load. At emergency load displacement, the mean draft was. At design combat displacement of, the mean draft was and metacentric height was.The Montana design shares many characteristics with the previous classes of American fast battleships starting from the North Carolina class, such as a bulbous bow, triple bottom under the armored citadel, and twin skegs in which the inner shafts were housed. The Montanas overall construction would make extensive use of welding for joining structural plates and homogeneous armor.
Armament
The armament of the Montana-class battleships would have been similar to the preceding Iowa-class battleships, but with an increase in the number of primary guns and more potent secondary guns for use against enemy surface ships and aircraft. Had they been completed, the Montanas would have been gun-for-gun the most powerful battleships the United States had constructed, and the only US battleship class that would have rivaled the Imperial Japanese Navy battleships Yamato and Musashi in armament, armor, and displacement.Main battery
The primary armament of a Montana-class battleship would have been twelve /50 caliber Mark 7 guns, which were to be housed in four three-gun turrets: two forward and two aft. The guns, the same used to arm the Iowa-class battleships, were long – 50 times their bore, or 50 calibers, from breechface to muzzle. Each gun weighed about without the breech, or with the breech. They fired armor-piercing projectiles at a muzzle velocity of, or high-capacity projectiles at, with a range of up to. At maximum range the projectile would have spent almost 1½ minutes in flight. The addition of the No. 4 turret would have allowed Montana to overtake Yamato as the battleship having heaviest broadside overall; Montana and her sisters would have had a broadside of vs. for Yamato. Each turret would have rested within an armored barbette, but only the top of the barbette would have protruded above the main deck. The barbettes would have extended either four decks or five decks down. The lower spaces would have contained rooms for handling the projectiles and storing the powder bags used to fire them. Each turret would have required a crew of 94 men to operate. The turrets would not have been attached to the ship, but would have rested on rollers, which meant that had any of the Montana-class ships capsized, the turrets would have fallen out. Each turret would have cost US$1.4 million, but this figure did not take into account the cost of the guns themselves.The turrets would have been "three-gun", not "triple", because each barrel would have elevated and fired independently. The ships could fire any combination of their guns, including a broadside of all twelve. Contrary to popular belief, the ships would not have moved sideways noticeably when a broadside was fired. The guns would have had an elevation range of −5° to +45°, moving at up to 12° per second. The turrets would have rotated about 300° at about 4° per second and could even be fired back beyond the beam, which is sometimes called "over the shoulder". Within each turret, a red stripe on the wall of the turret, just inches from the railing, would have marked the boundary of the gun's recoil, providing the crew of each gun turret with a visual reference for the minimum safe distance range.
Like most US battleships in World War II, the Montana class would have been equipped with a fire control computer, in this case the Ford Instrument Company Mk 1A Ballistic Computer, a rangekeeper designed to direct gunfire on land, sea, and in the air. This analog computer would have been used to direct the fire from the battleship's big guns, taking into account several factors such as the speed of the targeted ship, the time it takes for a projectile to travel, and air resistance to the shells fired at a target. At the time the Montana class was set to begin construction, the rangekeepers had gained the ability to use radar data to help target enemy ships and land-based targets. The results of this advance were telling: the rangekeeper was able to track and fire at targets at a greater range and with increased accuracy, as was demonstrated in November 1942 when the battleship engaged the Imperial Japanese Navy battleship at a range of at night; the Washington scored at least nine heavy caliber hits that critically damaged the Kirishima and led to her loss. This gave the US Navy a major advantage in World War II, as the Japanese did not develop radar or automated fire control to the level of the US Navy.
The large caliber guns were designed to fire two different 16-inch shells: an armor-piercing round for anti-ship and anti-structure work, and a high-explosive round designed for use against unarmored targets and shore bombardment. The Mk. 8 APC shell weighed in at, and was designed to penetrate the hardened steel armor carried by foreign battleships. At, the Mk. 8 could penetrate of vertical steel armor plate. For unarmored targets and shore bombardment, the Mk. 13 HC shell was available. The Mk. 13 shell could create a crater wide and deep upon impact and detonation, and could defoliate trees from the point of impact.
The final type of ammunition developed for the 16-inch guns, well after the Montanas had been cancelled, were W23 "Katie" shells. These were born from the nuclear deterrence that had begun to shape the US armed forces at the start of the Cold War. To compete with the United States Air Force and the United States Army, which had developed nuclear bombs and nuclear shells for use on the battlefield, the Navy began a top-secret program to develop Mk. 23 nuclear naval shells with an estimated yield of 15 to 20 kilotons. The shells entered development around 1953, and were reportedly ready by 1956; however, only the Iowa-class battleships could have fired them.
Secondary battery
The secondary armament for Montana and her sisters was to be twenty /54 cal guns housed in ten turrets along the superstructure island of the battleship; five on the starboard side and five on the port. These guns, designed specifically for the Montanas, were to be the replacement for the /38 cal secondary gun batteries then in widespread use with the US Navy.The 5-inch/54 cal gun turrets were similar to the 5-inch/38 cal gun mounts in that they were equally adept in an anti-aircraft role and for damaging smaller ships, but differed in that they weighed more and fired heavier rounds of ammunition at greater velocities, thus increasing their effectiveness. However, the heavier rounds resulted in faster crew fatigue than the 5-inch/38 cal guns. The ammunition storage for the 5-inch/54 cal gun was 500 rounds per turret, and the guns could fire at targets nearly away at a 45° angle. At an 85° angle, the guns could hit an aerial target at over.
The cancellation of the Montana-class battleships in 1943 pushed back the combat debut of the 5-inch/54 cal guns to 1945, when they were used aboard the US Navy's s. The guns proved adequate for the carrier's air defense, but were gradually phased out of use by the carrier fleet because of their weight.
Anti-aircraft batteries
While the Montana class would not be designed principally for escorting the fast carrier task forces, they would have nonetheless been equipped with a wide array of anti-aircraft guns to protect themselves and other ships from Japanese fighters and dive bombers. If commissioned, the ships were expected to mount a considerable array of Oerlikon 20 mm and Bofors 40 mm anti-aircraft weapons.The Oerlikon 20 mm anti-aircraft cannon was one of the most heavily produced anti-aircraft guns of World War II; the US alone manufactured a total of 124,735 of these guns. When activated in 1941, these guns replaced the.50 in /90 cal M2 Browning MG on a one-for-one basis. The Oerlikon 20 mm AA gun remained the primary anti-aircraft weapon of the United States Navy until the introduction of the 40 mm Bofors AA gun in 1943.
These guns are air-cooled and use a gas blow-back recoil system. Unlike other automatic guns employed during World War II, the barrel of the 20 mm Oerlikon gun does not recoil; the breechblock is never locked against the breech and is actually moving forward when the gun fires. This weapon lacks a counter-recoil brake, as the force of the counter-recoil is checked by recoil from the firing of the next round of ammunition. Between December 1941 and September 1944, 32% of all Japanese aircraft downed were credited to this weapon, with the high point being 48% for the second half of 1942. In 1943, the revolutionary Mark 14 gunsight was introduced, which made these guns even more effective. The 20 mm guns, however, were found to be ineffective against the Japanese kamikaze attacks used during the latter half of World War II. They were subsequently phased out in favor of the heavier 40 mm Bofors AA guns.
The Bofors 40 mm anti-aircraft gun was used on almost every major warship in the US and UK fleet from about 1943 to 1945. Although a descendant of German, Dutch, and Swedish designs, the Bofors mounts used by the US Navy during World War II had been heavily Americanized to bring the guns up to the standards placed on them by the Navy. This resulted in a gun system set to British standards with interchangeable ammunition, which simplified the logistics situation for World War II. When coupled with hydraulic couple drives to reduce salt contamination and the Mark 51 director for improved accuracy, the Bofors 40 mm gun became a fearsome adversary, accounting for roughly half of all Japanese aircraft shot down between 1 October 1944 and 1 February 1945.
Propulsion
The propulsion plant of the Montanas would have consisted of eight Babcock & Wilcox two-drum boilers with a steam pressure of and a steam temperature of feeding four geared steam turbines, each driving one shaft with ; this would result in a total propulsive power of, which gave a design speed of 28 knots at 70,500 tons displacement. While less powerful than the powerplant used by the Iowas, the Montanas plant enabled the machinery spaces to be considerably more subdivided, with extensive longitudinal and traverse subdivisons of the boiler and engine rooms. The machinery arrangement was reminiscent of that of the, with the boiler rooms flanking the two central turbine rooms for the inboard shafts, while the turbine rooms for the wing shafts were placed at the after end of the machinery spaces. Montanas machinery arrangement combined with increased power would eventually be used on the. The Montanas were designed to carry of fuel oil and had a nominal range of at. Two semi-balanced rudders were placed behind the two inboard screws. The inboard shafts were housed in skegs, which while increasing hydrodynamic drag, substantially strengthened the stern structure.To meet the high electrical loads anticipated for the ships, the design was to have ten 1,250 kW ship service turbogenerators, providing a total of 12,500 kW of non-emergency electrical power at 450 volts alternating current. The ships would also be equipped with two 500 kW emergency diesel generators.
Armor
Aside from its firepower, a battleship's defining feature is its armor. The exact design and placement of the armor, inextricably linked with the ship's stability and performance, is a complex science honed over decades. A battleship is usually armored to withstand an attack from guns the size of its own, but the armor scheme of the preceding North Carolina class was only proof against shells, while the South Dakota and Iowa classes were designed only to resist their original complement of Mk. 5 shells, not the new "super-heavy" Mk. 8 armor-piercing shells they actually used. The Montanas were the only US battleships designed to resist the Mk. 8, and were designed to give a zone of immunity against fire from 16-inch/45-caliber firing shell, between 18,000 and 31,000 yards and 16-inch/45-caliber firing shell, between 16,500 and 34,500 yards away.As designed, the Montanas used the "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. 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 armor mounted on Special Treatment Steel, 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 was 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, consisting of STS laminated on STS for a total of STS weather deck, Class B laminated on STS for a total of second deck on the centerline, and a splinter deck; the outboard section would have Class B laminated on STS for a total of second deck and a splinter deck. Over the magazines, the splinter deck would be replaced by a STS third deck to protect from spalling.
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 "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. 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 Montanas would allow a higher system depth of compared to of the North Carolinas.
Until the authorization of the Montana class all US battleships were built within the size limits for the Panama Canal. The main reason for this was logistical: the largest US shipyards were located on the East Coast of the United States, while the United States had territorial interests in both oceans. Requiring the battleships to fit within the Panama Canal took days off the transition time from the Atlantic Ocean to the Pacific Ocean by allowing ships to move through the canal instead of sailing around South America. By the time of the Two Ocean Navy bill, the Navy realized that ship designs could no longer be limited by the extant Panama Canal and thus approved the Montana class while simultaneously planning for a new third set of locks that were wide. This shift in policy meant that the Montana class would have been the only World War II–era US battleships to be adequately armored against guns of the same power as their own.