Introduction

In this three-part ‘reloaded!’ article we will take a bit wider perspective look on the USN capital ship program of the late 1930s and early 1940s with primary focus still on the Montana class. Since most other navies designed and built only one or maximum two classes of 1st rate capital ships in the same period these can be dealt with separately. However the US Navy designed and built four consecutive classes and these all answered different challenges. Their designs were somewhat parallel (especially in the case of the final two classes) and their planning&construction period was so compressed that it is impossible to look at the Montanas without going into some detail about the predecessor units.

The major lesson of our story it is that even when all external limitations are cut back to a minimum battleship design is still a very delicate balancing act.
The preliminary design process was heavily burdened by naval treaty obligations and even the finalized designs bore some political influence. The BB-67 class as finally approved for construction appeared to be an unlimited design on paper only – under the surface it still gave up a lot. Designers and future operators alike were stunned how much remained to be addressed to reach the ultimate battleship.
Their humongous size and massive firepower combined with first class protection represented an entirely different level to all previous US battleship. As we will see this very fact and their prolonged gestation period led to the cancellation of the entire class and therefore left the Japanese Yamato class to take the crown as king of all gun armed warships.

Prelude

Warships and especially battleships always represented a major capital expense for any nation, even for the United States. It is no wonder that politicians and democratic governments tried to burden naval planners with financial restrictions, sometimes even law enforced.

Steel built capital ship progression was pretty slow and was happening on many independent threads in the first years from USS Monitor and HMS Warrior up to the early 1890s. By that time most of the navies have arrived to a form and size that was deemed optimal and cost effective enough to build up a fleet of repeat designs with relative minimal changes. Ships were in the 10.000 tons range, about twice the size of the original iron armor clad ships of the line from the 1860s. From 1890 until 1900 battleship size hardly grew and this was the period when the USN entered the game in earnest, being a solely coastal defense force in the past decades. During this period the following classes entered service:

• BB-1-3 Indiana class 1895 (10.200t) – still limited to coastal ops.
• BB-4    Iowa 1897 (11.400t)
• BB-5-6 Kearsarge class 1900 (11.540t)
• BB-7-9 Illinois class 1901 (11.600t)

International trend however went into the direction of heavy secondary batteries. As naval gun development enabled quick firing (several times per minute) for these smaller caliber weapons (5-8″) they started to pose a menace to lightly armored or unarmored upper works at the then prevalent short battle ranges. Armor also improved, while speeds were somewhat increased. All these required bigger ships, so the 1901-1906 period was defined by more substantial increases in displacement and therefore cost. US Congress limited displacement to 16.000 tons in order to keep battleship growth (that is cost) in check. However even these increased displacement/cost units were relatively sustainable and at least the newer ships did not completely obsolete previous classes. The following mixed-battery battleship classes were procured by the USN in this period:

• BB-10-12 Maine class 1902 (12.800t)
• BB-13-17 Virginia class 1906 (14.900t)
• BB-18-19 Connecticut class 1906 (16.000t)

In 1906 HMS Dreadnought commissioned. Even though the USN contemplated single major caliber battleships as early as 1902 serious design work was not undertaken on these until about 1903-04. To bring up numbers the then running program of battleship construction (authorized already in 1903) was rounded out, before any dreadnought category ships were laid down. These included ships with both 8″/203mm and 7″/178mm secondary batteries and a final class with reduced displacement, exactly to cut back growth (cost) as it took on an alarming rate from BB-7 class to BB-18 already.

• BB-20-22, 25 Vermont class 1907 (16.000t)
• BB-23-24 Mississippi class 1908 (13.000t)

With the 16.000t Congress mandated displacement limit still in place the USN designers had no choice but to fit their first dreadnought battleship into that range. This meant that even using the ingenious super-posed centerline turrets speed was limited to 18 knots. The turbines were no option yet for the USN and there was no more displacement left for a bigger VTE machinery. What’s more the belt armor was not uniform thickness, again in order to limit size. Slow pace of construction prevented these units from joining the navy before 1910, making them almost obsolete by then (compared to British and German dreadnoughts already in service).

• BB-26-27 South Carolina class 1910 (16.000t)

From this point on with the dreadnought ‘fever’ raging among the world navies displacement started to escalate really quickly and newer and newer classes made the previous generations totally obsolete:

• BB-28-29 Delaware class 1910 (20.300t)
• BB-30-31 Florida class 1911 (21.800t)
• BB-32-33 Wyoming class 1912 (26.000t)
• BB-34-35 New York class 1914 (27.000t)

It is clear from the above list that displacement grew as much in a few years as it did in the previous few decades altogether. The Wyoming and New York classes were already deeply influenced by the Newport Conference of 1908 where the future US battleships were envisioned as the most powerful and longest ranged units possible (with a Pacific war in mind) . Congress tried to limit things by hard capping hull cost at 6M USD apiece. The General Board also came to power during this time, sanity controlled by the civil Secretary of the Navy. This position was held by Josephus Daniels in the coming years and he did remarkably well to keep ship growth in check. Up until the 1916 naval program (that decided ships for Fiscal Years 1919 and onwards) battleship growth was again stagnating within the USN. Foreign navies, except for the Japanese and a few British ships also hovered around this size as war efforts precluded the bigger ships on the building ways to be completed.

• BB-36-37 Nevada class 1916 (27.500t)
• BB-38-39 Pennsylvania class 1916 (31.400t)
• BB-40-42 New Mexico class 1917 (32.000t)
• BB-43-44 Tennessee class 1920 (32.300t)

The 1916 naval program represented the US answer to the ongoing war. Had it gone through it would have established the USN as the world’s premier naval force by ordering an unprecedented 10 battleships and 6 battle cruisers, all with 16″/406mm main guns. To put the magnitude of this program into perspective this force (if completed) would have been equal or probably even higher military value than all the other classes listed so far, combined. No wonder that with the end of the Great War these units came under intense public and political scrutiny.

• BB-45-48 (BB-47 cancelled) Colorado class 1921 (32.600t)
• BB-49-54 (all cancelled) South Dakota class (43.200t)
• CC-1 -6 (4 canc., 2 converted to CV) Lexington class (43.500t)

US foreign diplomacy cleverly used this change in political and public sentiment to set up a global arms limitation agreement with all the major naval powers. (Most probably though the program would have been cancelled or cut back anyway irrespective of the resulting treaty.) Clearly it was aimed at Japan first and foremost and the UK second, who were allied at the time. With the Washington Naval Treaty of 1922 the USN reached parity with the RN without having to invest huge sums of money into the above listed capital ships and still kept the Japanese at bay.

Professional opinion was mounting against the battleship as well with the aircraft demonstrating it’s efficiency during the closing years of the Great War. Performance of newer, more advanced types was even more convincing. There were some publicity stunts (like General William ‘Billy’ Mitchell’s test against the ex-German Ostfriesland) which portrayed the aircraft as the new king of the seas . On the other hand the Navy ran it’s own, more professional and controlled tests which showed much more underwhelming results. It was enough, however to justify the General Board’s efforts put into carrier designs. Still, the battleship’s position was somewhat questionable during the late 1920s and early 1930s.
It is very important to point out though that for the first time in history, a weapon (system) was internationally limited in it’s development and the competing weapons and anti-measures (chiefly the aircraft and the torpedo) were not! Therefore when capital ship construction resumed in the mid 1930s the new ships had to contend against threats a complete generation or two ahead of them and doing this with displacement (that is capability) severely limited. The 35.000 ton displacement – 16″ inch gun caliber limit combo of the Washington Treaty essentially cut off battleship development where it was at the end of the Great War.

A look at the Treaty System

The Five Power or Washington Naval Treaty of 1922 is well known and I would like to keep it’s details to a relevant minimum here. What is usually less well known or less publicized are the follow-up agreements, the First and Second Naval Treaty of London, ratified in 1930 and 1936 respectively.

The Washington Treaty set up a complete ban on capital ship construction among the United States, the United Kingdom, the Japanese Empire, the Republic of France and Italy which was set to expire on the 31st December 1931. New construction after this date could not exceed 35.000 tons of standard displacement* and were not allowed to mount any guns in excess of 16″/406mm. However the Treaty allowed for 3.000 tons of displacement increase for each existing unit under the provision that it is used for upgrading and enhancing the anti-aircraft and anti-torpedo capabilities. The total tonnage of capital ships (that also meant the number of hulls) were limited for each Navy. Each capital ship could only be replaced on a one-for-one basis after 20 years of life (counted from keel laying). The Royal Navy got an exception for new construction, they were allowed to build two brand new battleships, respecting the treaty’s limitations and scrapping 4 older units in return. These ultimately resulted in the Nelson class, which set the benchmark for all post treaty new construction. The Marine Nationale and Regia Marina were each allowed to replace three of their eldest capital ships with new construction before the Treaty’s expiration date as their displacement quotas were filled out by pre-dreadnought ships.

*Standard displacement as defined by the Washington Treaty meant the weight of the ship fully armed, equipped and ready for sea excluding fuel and boiler feed water. It got introduced as a common nominator for all navies that allowed for comparison between ships designed for widely different areas of operation. All ship tonnage values in this article are given as standard displacement.

The First Naval Treaty of London held in 1930 further extended the battleship building ‘holiday’ or moratorium until end of December, 1936. It kept and further reduced the total tonnage limits leading to the scrapping of several older ships. They wanted to bring down the unit displacement limit to 32.500 t (even 17.500 tons was proposed at one point) – the US insisted on 35.000 tons and it stayed. There were disagreements on the cruiser side of things as well (there happened to be a failed conference in Geneva in 1927 dedicated to the cruiser question). All in all this was clearly in contrast to the 1922 Treaty with mutual agreement among the parties completely gone. Japan was still upset by it’s lesser quota, Italy and France were in no financial state to immediately think about major new construction and finally the Soviet Union was a no show invitee.

In late 1935 the powers met again in what we know as the Second Naval Treaty of London. From the get go it seemed that the chances for a new, internationally accepted agreement are very slim.
Additionally there were several new developments in the naval world that deeply influenced matters:

• first of all the German ‘Panzerschiff’ appeared: it was markedly faster compared to any existing battleship and boasted a powerful enough armament that any treaty limited cruiser had to think twice of even approaching a Panzerschiff. Only the British and Japanese battlecruisers were fast and capable enough to run these down with superior firepower and protection; the USN had no gunship that could take on them
• Italy had the first entirely new generation 35.000 ton battleships laid down in 1934; although they were reported to be in accordance with the displacement limit, both France and Great Britain were skeptical about that (in fact the ships as completed approached 38.000t with 15″/381mm guns)
• However from a US point of view by far the most problematic were the Japanese, who demanded parity with them and the UK

Needless to say neither the US nor the UK agreed to this. Combined with the recent sanctions imposed by the League of Nations on Japan due to the Manchurian Affair the Japanese were quick to denounce their Washington and 1st London Treaty obligations and left the talks. Italy followed suit soon.

It remained for the US, the UK and France to reach some kind of further agreement, but it was really only important for the British (to keep their force value high) as they desperately wanted to keep gun and ship size to the smallest possible. They proposed 12″/305mm gun and 25.000t displacement limits, hoping to reach a compromise with the US somewhere around the 14″/356mm – 30.000t mark. The US agreed in the end to keep the 14″/356mm limit on guns, however in light of a very possible Pacific War they insisted again on the 35.000t limit. Total tonnage and hull number limits were also gone. Papers were signed on March 25, 1936.
Since two of the original five signatories were out an escape or escalator clause was put in: if by 1st April 1937 either Japan or Italy fails to agree to the 14/356mm” limit then the new limit is again 16″/406mm for all signatories. As we know now Japan announced on March 27th that they won’t agree to the caliber reduction, quite late in the design process for some USN/RN ships. Basically this meant the beginning of the end for the treaty system as it was pretty obvious that Japan would exceed these limits.

There was a further amendment (Article 25) or clause included in the Second London Naval Treaty, that gave the right to the signatories to deviate from the agreed limits should any of the non-signatory naval powers authorize, construct or acquire ships that are in excess of said limits. Consequently after brief news about newly laid down Japanese battleships displacing 46.000 tons and armed with 16″/406mm guns circulated in the naval world all three signatories invoked Article 25 on the 31st March, 1938 and formally signed an agreement in July to raise allowed displacement to 45.000t while keeping the 16″/406mm maximum on guns. This was still a conservative upper cap as unofficial murmur hinted at possible 18″/457mm guns for the Japanese ships and even bigger displacements than what was officially reported (which made sense if the bigger guns were to be believed).

After this the whole Treaty system lasted for little longer than a year and completely abandoned by all three members on 1st September 1939.

Factors impacting New Construction

From the cancellation of the 1916 program hulls by the Washington Treaty up until late 1937 there was no gun armed capital ship keel laid in the United States. The General Board and the Construction & Repair bureau (mainly it’s Preliminary design branch) still devoted resources and time to prepare designs just after 1922 and again in the late ’20s to prepare for the London conference.
As expected due to the treaty limitations the focus of battleship design shifted from increasing gun power and armor protection to the most efficient use of the allotted, fairly tight 35.000 tons displacement. Long range firecontrol (even beyond horizon), anti-aircraft firepower and protection measures against air dropped ordnance became primary factors, besides speed and range. In other words every navy was given the difficult task of working a lot more military value and capability into almost the same displacement as they had at the end of the Great War.

Design work picked up in earnest during 1934-35 when the approaching end of the battleship ‘holiday’, 1st January 1937 was already in sight. However there were three factors that directly influenced the US Navy’s new construction battleships besides the treaties and obvious political and financial restrictions.

1.\ The role of the battleship as the main fighting unit of the Navy was challenged many times during the ’20s. The General Board and influential politicians (including Roosevelt) and naval personnel believed that it was here to stay. After all the battleship proved it’s power in many wars. However the Naval War College and it’s wargames – supplemented by the real life Fleet Problem exercises conducted in the 30s – that were absolutely essential in developing navy tactics showed very well the combat power and capabilities of modern carriers and long range submarines. Still there were many tasks that only battleships could accomplish; like night or bad weather combat, area-denial missions but most importantly the assured destruction of enemy surface units, including battleships. Carriers were acting more as a support unit that were essential in scouting and first strikes (which tried to take out the enemy carriers thus depriving the enemy battlefleet of it’s most powerful scouting asset), however the decisive blow was still dealt by the battleline, that is the massed group of battleships.
Also without a massive supporting fleet train (as of yet) the carriers were mostly one hit wonders, the initial large aircraft contingent strikes dealing the most damage then every follow-up attack being less and less powerful due to the extremely high losses to enemy fighters and AA. Aircraft were also much less effective against smaller, faster and more maneuverable targets like cruisers and especially destroyers – most air dropped torpedoes being slower than these ships and dive bombers being in their early development stages only.
The wargames overestimated a bit the power of aircraft that were available in the 30s but they also badly overestimated the efficiency of the then existing anti-aircraft guns.
Finally there was one thing that only the battleships had and that was the ability to take massive damage and still continue to fight. Wargaming showed that even a single, relatively small bomb hit on a carrier’s flight deck could render the whole ship incapable of launching or recovering aircraft, that is preventing it from using it’s “main battery”. (This is why the US Navy went for non-armored, double ended flight decks). The same bomb hit – bar a very lucky hit through the funnel – would hardly impact a battleship’s fighting power.
Fortunately in the end a balanced fleet concept was sought after, first with the battleship as the backbone and everything else centering around the massed battlefleet. As the tabletop simulations progressed the concept of task forces with mixed battleship and carrier setups came to be the most logical way of employing these assets. However the existing slow US battleships massively limited the tactical mobility of the carriers – but admirals were reluctant to release the CVs for independent operations due to their vulnerability, especially in less than ideal weather or light conditions. Therefore fast capital ships were sought after to work with the carriers. Even then for a long time the final decisive, Jutland style battle was still on the agenda, and that required all the battleships concentrated into one fleet with no detached operations.

This whole mindset required the General Board to frontload it’s future building plans with battleship construction. These took the most time to build, especially guns, turrets and heavy armor: manufacturing these sometimes took years before actual hull construction even started. Also carriers can be converted from other ship types in an emergency but there appeared to be no quick replacement for a fully fledged battleship in case of war. And this leads us to point number

2.\ which is the lack of a proper industrial background in the mid ’30s. The first and biggest bottleneck was the number of available, large enough slipways where capital ships could be constructed. The state/public owned navy yards had five such slipways split between the New York Navy Yard (2), the Philadelphia Navy Yard (2) and the Norfolk Navy Yard (1). Even then for the two twin slipway yards to be able to simultaneously build two ships they required massive expansion in their supporting infrastructure (223M USD).
Potentially there were 6 additional, privately owned slipways that could be used, equally divided between the New York Shipbuilding and DryDock Company, the Newport News SB&DD Co. and the Bethlehem Steel’s Quincy Shipyard. Using private shipyards had a lot of drawbacks though as they were a lot costlier (on avrg. 61M for a single hull vs 41M in a public yard) and any change to the ship’s design after the contracts are signed would be much more difficult and even more expensive. Also some infrastructural shortcomings were present at these builders as well and these needed remediation by using public money (141M USD)! Since carrier construction required long slipways as well even this was not enough and in 1940 Congress authorized money for 5 large graving docks to be built at the Navy Yards, but these would take at least a year to be completed before any new construction could be laid in them.
The second concern was heavy armor manufacturing capacity, or the lack of it. In the wake of the 1922 Treaty most of the steel manufacturing companies gave up their gear and know-how as potentially there was no need for these. In 1939 the total yearly output lay around 19.000 tons of heavy armor plating. In contrast a single 35.000 ton battleship needed about 15.000 tons of armor, and by 1939 five ships were already on the slipways and a further three hulls under order. Since the installation of heavy armor plates making-up decks and main bulkheads occur relatively early in the construction this protruded as a sore point. Again a huge sum of money (~200M USD) got poured into upgrading and expanding equipment of both publicly and privately owned firms. Therefore by late 1940 annual capacity exceeded 40.000 tons and after Pearl Harbor even more was invested: by late 1942 the monthly output reached 15.000 tons!!!
Finally gun forging and turret machinery remained as potential bottlenecks. Fortunately some mitigating factors entered the picture here. These parts were needed only relatively late in the construction schedule, well after the launching of the hull. Also a large number of guns and pieces of turret machinery were left over from the 1916 capital ship program that could be re-utilized. Furthermore the Naval Gun Factory and two private firms have kept most of the equipment and know-how since large caliber guns needed periodic overhauls that is re-lining and even replacement which essentially meant that new guns were still needed due to normal wear/tear from usage. To make things better some money flowed in here as well into a second public factory, the Naval Ordnance Plant that could take on most of the relining work from 1943 onwards. All in all the re-conditioning of the background industry essential for the new capital ship program cost well over half a billion tax dollars!

3.\ Finally the question of what exactly to build remained and this proved to be one of the hardest nuts to crack. The General Board was still the topmost naval (professional) authority to decide this, however there were many inputs on the topic coming from the President/Secretary of the Navy (political), the Naval War College and the Chief of Naval Ops (tactical), the partly civil Battleship Advisory Board (technical) set up in 1937 down to various admirals (operational) holding active sea duty positions etc. As can be expected with so many having a say in the matter there happened to be a lot of conflicting opinions and interests.
The two chief points of opposition were:
1.\ reaching a decision between the option of slow (21kn), well protected and very well armed ships for battleline operation versus fast (26kn+) but relatively lightly armed and armored ships intended for task force actions (that is working with carriers).
2.\ setting the caliber of the main battery. This was not so much a professional question as almost unanimously the 16″/406mm gun was favored. It was of course a politically induced one as a consequence of the London treaties and the international situation. The potential future enemy for the US in the 1930s was Japan and therefore most of the strategic planning prepared against them. However there was pretty limited trustworthy intelligence information available about what the Japanese planned to build and what they did during reconstruction to their existing ships. Therefore planners still took the Royal Navy and it’s ships as a benchmark, of course not as a probable future adversary but as a technically advanced “competitor”.
Before we continue to the actual ship classes built as an answer to the above questions we have to take a look at the raison’de étre for battleships: heavy naval guns!

Note: to keep the text simple I’ll use the official name of the guns only, deferring the metric conversions in the names; other values are always imperial first / metric second

Available guns and related concepts

When the Washington Treaty hit in 1922 there were 3 primary naval rifles in service or under development within the USN. These were the:

• 16″/45 Mark 1 (arming the first class of the 1916 program, the Colorados);
• 16″/50 Mark 2 (arming the rest of the 1916 program);
• 18″/48 Mark 1 still under development/construction.

The latter weapon was in it’s trial phase only, with one ~50% complete example. It was intended for potential future battleship classes, but only some rough preliminary designs calculated with them. (On the drawing boards there was a further, 20″/508mm monster as well, however we know very little about this gun.)
Since caliber was tied to 16″/406mm there was no point in finishing this 18″/457mm rifle as such and it was decided to convert it to a treaty compliant option. A very thick walled, 16″/406mm diameter inner tube or liner was inserted into the re-threaded and somewhat modified barrel. As a result they got the 16″/56 Mark 4 (Mark 3 was a slightly modified Mark 2). Muzzle speeds came in at an extra-ordinary 3000 feet/sec / 914 m/s for the Mark 4 with the standard 2100 pound/ 952kg AP shell. This value was 2800/853 and 2600 fps/ 792 mps respectively for the shorter barreled Mark 2 and Mark 1.

There were several tests conducted with all of these guns during 1926-1927 as it was expected that battleship construction would continue after 1930. Before we look at test data two relevant concepts might need some explanation: the Immunity Zone (IZ) and the Danger Space (DS).

The IZ of a given battleship versus a given gun/shell combination is defined by the range band where it’s armor can NOT be penetrated by said weapon system. As the above visual example shows the target ship has an IZ vs the 16″/45 between 18.000 and 30.000 yards (16.460-27.430 m). That means it’s belt armor can not be penetrated at greater than 18.000 yards range by this gun and it’s decks are safe out to 30.000 yards. If the same target faces the 16″/50 with it’s higher muzzle speeds the belt can be penetrated out to 21.700 y/19.850 m however decks would be safer further out as well, to 32.100 y/29.350 m.
Things are further complicated by the DS of a given gun/shell combo. The higher the muzzle speed is (due to lighter shell and/or longer barrel) the bigger the danger space will be, which is the range error where within the shell would still hit.
The longer the gun the flatter it’s shell’s trajectory (and smaller it’s dispersion) is, meaning that hits would be more numerous and tend to be closer to perpendicular on the belt even for longer distances. On the disadvantage side deck hits at the same distance would be at a shallower angle, reducing penetration. Furthermore hit distribution for 16″ guns starts to be heavily in favor of deck hits (ie horizontal) instead of belt hits (vertical) from about 25.000 yards (~22km) outwards.
In other words a shorter gun is preferable for deck penetration at longer ranges and a longer gun is preferable against belts, especially at sub 15.000 yards (13.7km).

Tests showed very nicely that a target object armored similarly to a standard battleship (Nevada to Colorado class) with 13″/330mm belt and 3.5″/90mm deck armor had no IZ at all against the Mark 4 gun with it’s phenomenal 3000 fps/914mps muzzle speed (shells could penetrate the belt out to 28.8ky/26.3km and the decks from 28ky/25.6km). However most of the hits were on the deck (about 75-80%) at these distances and the shorter Mark 2 and Mark 1 guns could penetrate the same deck with the same AP shell already at 26.300 and 24.600 yards respectively (24 and 22,5km).

As a conclusion the 16″/50 Mark 2 was the preferred gun option for future new ships as it had best of both worlds while being lighter, cheaper and also more affordable to reline.
In 1930 the London Treaty however did not increase displacement, so something lighter but still powerful enough was sought next to the 16″/50 Mk 2. Development started in 1936 on a new, lightweight 16″/406mm gun, in expectation of new construction from 1937 onwards.

This was the 16″/45 Mark 6 which intended to fire a new, so called “heavy” 2240 pound (1016kg) AP shell (Mk. 5), while thanks to new construction methods gun weight was kept close to the 100 ton mark (in comparison the Mark 4 weighed in at 188 tons and the Mark 2 at around 130 tons). With the Second London Treaty the caliber limit was reduced somewhat unexpectedly, therefore a rush program to develop a modern 14″/356mm weapon, the 14″/50 Mark B started in late ’36, early ’37. In the end no prototype got ever produced as after the Japanese refusal to accept the 14″/356mm limit in March 1937 development stopped completely and focus shifted back to the Mark 6. Two more weapons entered the picture in 1939 and 1940 respectively:

• the 16″/50 Mark 7
• and the 18″/47 Mark A that was in fact the re-converted 16″/56 Mark 4 with the extra thick liner removed and threading cut down at the back (therefore it was now only 47 length instead of 48, as originally designed in it’s Mark 1 config.).

Both weapons were intended to be used with the new generation of so called “super-heavy” shells. The Mark 7 was again a light-weight gun at ~121 tons that came to be to fire the 2700 pound (1225kg) Mk.8 AP shell at 2470 fps/ 752 mps (later improved to 2500/762). This Mk.8 ammo gave excellent penetration capabilities, especially at longer ranges against decks, but due to it’s heavier weight maximum range suffered, especially when fired from the Mark 6 gun; that is mainly the reason why the Mark 7 was designed. Due to the increased length (72″/183cm) the Mk.8 ammo could not be used with the Mark 1 and Mark 2 guns with their existing mount’s loading mechanisms. It is worthy to note that even 3150 pound (1429kg) AP shells were tested but these gave unsatisfactory results due to the extremely long shell bodies as they tended to break up on oblique impacts (above 30°). The finally commissioned Mk.8 had this tendency as well but to a much lesser degree and the Mk.8 Mod.6 redesign with a more rounded projectile nose introduced in late 1944 completely removed this issue.

Interest in the 18″/457mm caliber also revived around 1938-40 after several rumors had been circulated about the new Japanese BBs mounting a similar diameter gun. The 16″/56 Mark 4 mentioned above had been viewed for long as the optimal battleship gun as it offered excellent penetration and very little dispersion. Firing the 3150 lb/1429kg shell it also excelled at and even rivaled 18″/457mm weapons in penetration capabilities. On the downside the extreme muzzle speeds taxed the liner tubes so much that their service life was only 50 full effective rounds on the test gun*. The enormous weight and length of the barrel meant that it needed mounts in the 18″/457mm category. It was expected that an 18″/457mm caliber gun with a heavy weight shell would perform similarly and would be lighter/cheaper and sport a much longer liner life. Therefore the sole existing 16″/56 Mark 4 was ordered de-linered and re-converted and with the interim designation Mark A the 18″/47 re-appeared in Sept. 1941. A thorough test firing program followed over the coming year: “The highest energy shot ever fired from this gun (376M foot-pounds/~510MJ) was with a 3,848-lb. (1745kg) projectile using 910 pounds (413kg) of IHIC Sample 2 powder. This proof shot was the highest energy shot ever fired from an American gun. The muzzle velocity for this shot was 2,508 fps (765mps) and the maximum pressure was 19.91 tons per square inch (2758 bar).” – Source

Needless to say this gun in this configuration could have easily defeated most battleship’s armor then in existence, with a quoted deck/horizontal penetration capability of 6.25″ at 25.000 yards (158mm/22,8km). The Japanese Yamato class were the only one that had a meaningful IZ versus this weapon.

*Note: Actual liner life is reported between 120-150 shots by various sources. However standard USN practice called for re-linering a gun after the remaining life of it decreased below the ammunition load-out, usually 90-100 rounds per gun. This way worn out guns could not limit gunnery performance in a critical situation. Later production variants of this weapons would have improved on this issue as well.

 

Below table summarizes the above mentioned weapons’ most important specifications

(Note that the jump in penetration capabilities for the 2nd generation guns (1930+) are largely due to much improved AP shells)

Gun name	Year	Weight (t)	AP shell weig.(lb/kg)	Muzzle speed (f/m/s)	Pen. @90°@20kyard
16″/45 Mark 1	1913	107	2100 / 952	2600 / 792	11.5″/293mm (Mk.3 AP)
16″/50 Mark 2	1916	130	2100 / 952	2800 / 853	13.5″/343mm (Mk.3 AP)
16″/56 Mark 4	1922	188	2100 / 952	3000 / 914	13.0″/330mm @28.8kyard
14″/50 Mark B	1937	81 (est.)	1500 / 680	2700 / 823	14.0″/356mm (Mk. 16 AP)
16″/45 Mark 6	1936	103	2700 / 1225	2300 / 701	17.6″/447mm (Mk.8 AP)
16″/50 Mark 7	1939	121	2700 / 1225	2470 (2500)	20.4″/518mm (Mk.8 AP)
18″/47 Mark A	1940	180	3840 / 1742	2500 / 762	16.0″/406mm+ @25kyard

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After a very long hiatus in battleship construction the expectations were naturally sky high. The new ships had to answer multiple threats while keeping the firepower and protection of older generation units and still be faster than those: achieving all this with hardly 10% extra displacement proved to be a real challenge. The difficulty of this is well illustrated by the fact that overall more than 70 (!) preliminary designs were sketched up, by far the most for any major US warship.
Initial designs for the first Treaty battleship class of the USN can be traced back to 1934. In the first series running mostly up until 1936 a wide variety of concepts have been tried, answering all sorts of various internal requests. From very slow, heavily armed and/or armored variants up to battlecruiser like ships and including some off-springs with all-aft main batteries and all aviation facilities forward -requested by the President.
The main debate was really between:

• traditional heavily armed variants that gave up speed for massive armor protection
• and fast units that could operate with carriers but had to give up both protection and firepower to enable that

There were arguments for both, especially considering what the potential opponent, the Imperial Japanese Navy could field against these ships in the future. On one side there were the fast Kongo class battlecruisers, which were believed to be capable of 26-27 knots and posed a mortal threat to US carriers. On the other hand the Japanese were expected to construct new ships as soon as the existing treaty expires and this mandated classic american style battleships to oppose them. The former could easily do with nine 14″/356mm guns, the latter would only truly work with at least eight 16″-ers (406mm). As fate would have it the 1935-36 talks kept the caliber limit at 14″/356mm and what was worse Japan exited the agreement, so it was free to build bigger ships.

Therefore the second series included somewhat more refined versions and mostly used a middle-ground design philosophy to answer both threats. The slowest designs had a speed of 27 knots while the fastest could race along at 30-31 but gave up about 30% firepower in turn. In the end a revised form of Scheme XVI won, which was a 27 knotter sporting 14″/356mm guns in quad turrets, twelve barrels in total. Secondary battery was made up of twin and single turreted 5″/38 (127mm) dual-purpose guns, sixteen in total. Armor remained a sore point, especially underwater side armor was lacking. Critics already pointed out that the design, although balanced, did not excel in any of the classic triumvirate of speed/firepower/protection. Despite this the whole affair qualified as a success considering the severe restrictions that the 35.000 ton limit imposed.

The lightweight, high pressure/temperature machinery, with only four large machine rooms (instead of the turbo-electric drive’s massive subdivision) and the partly welded construction with every scantling and fitting cut to the minimum combined with longitudinal framing made it possible to achieve this.

There was an additional, yet un-played ace in the hands of the US designers. Thanks to sufficient resources and extra time before construction had to start two armament options were being developed:

• the 16″/45 Mark 6 gun with three gun mountings; although it was ruled out by the treaty yet considerable effort has been put into it already.
• at the same time a program started to develop a modern 14″/356mm gun mounted in quadruple, independently sleeved turrets as well. The mountings and loading mechanism for both guns were conceived in a way to fit into the very same barbette diameter!

Roosevelt himself postponed the new ships to FY38, meaning that building of the actual hulls would start only in the 2nd half of 1937. This implied that the US ships would be delayed substantially compared to the British King George V class – the Brits already made the decision for the 14″/356mm weapon in order to start building their ships by 1st Jan 1937. This in turn allowed that potential decision on what mounts and guns to use on the BB-55 class to be held off until the end of that year. Since Japan informed the Treaty participants on the 27th March 1937 about their non-acceptance of any limits the US was free to move on with the bigger guns. Even then Roosevelt was reluctant to commit. He did not want the US appearing as the enforcer of an international caliber race. Only after news came in from Germany and the Soviet Union about using 15″/381mm and even 16″/406mm guns for their new construction did the President give the order in July 1937 to go with the bigger caliber in a two forward – one aft three-gun turret layout.

The resulting final design therefore went from being well balanced between speed-firepower-protection to a massively overpowered, fast unit with somewhat lacking armor protection. The introduction of the Mk. 8 super-heavy AP shell made things even worse balance wise as the effective IZ was reduced to almost meaningless distances. (It was already only 21.000-27.700 vs the 2240 pound shell /19.2-25.3km vs 1016 kg/; in contrast to the original 19-33 kyards/17,3-30km vs the 1500lb/680kg – 14″/356mm shells).

In the meantime the design also progressed on many other points:

• the number of secondary guns got increased to 10 twin 5″/38 mounts (127mm), distributed equally on the two sides with 3-3 mounts on the upper (superstructure) and 2-2 on the lower or main deck level
• belt armor was to be mounted externally but at a fairly steep 15°angle (formerly it was 12°)
• to counter the threat of diving shells some armor patches were added on the magazines below the waterline, following the wave contour (see model above)
• a spoon shaped stern layout combined with the inner shafts placement in skegs provided a large enough stern area to house a crane and two catapults; the skegs also provided some form of defense from underwater explosions for the unopposed side’s shafts
• there was a main fire-control tower in the forward superstructure supplemented by a small, secondary one aft, behind the funnels; 4 high angle capable directors were used for the secondary battery with one forward, one aft and one on each side next to the funnels

Most of these features lasted as trademarks of modern US Navy battleships, with some variations they appeared on the subsequent BB-57 and BB-61 classes and actually some re-appeared in their original form on the BB-67 class.

The keel for BB-55 North Carolina was laid down in the New York Navy Yard in October 1937 and she completed in April 1941. BB-56 Washington started construction in Philadelphia NY only in June 1938 but commissioned in May 1941 already. The construction period was fairly long, especially for BB-55 due to the bottlenecks described in the prelude section. What’s worse severe vibration issues were encountered on trial runs for both units: so bad was the situation that for a period the ships were not allowed to accelerate above 23 knots. This problem sent shock waves through the Navy and especially the Bureaus involved in the design process. The issue encapsulated the possibility that subsequent ships would face the same phenomenon as they shared the machinery layout and skeg design. Fortunately more advanced, increased blade-count propellers and some bracing on the fire control equipment largely solved the issue, but it never completely went away.
Therefore real combat efficiency was only attained in early-mid 1942 but after the initial issues were ironed out the pair gave essential service in the 2nd half of the year in the battles around Guadalcanal. What’s more BB-55 had the bad luck to be the only one from the modern US Navy BBs that received severe underwater damage (from enemy action). It’s torpedo defense system, inherited from previous generation ships with it’s 5 bulkhead, liquid-void system stood up fairly well.

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In a strong contrast to proceedings so far both the political jiggling and the design gestation period was fairly short for the BB-57 class units.

On the political and financial side once the ball got rolling there was no stopping. The General Board already wanted 4 hulls back in 1936 built to the initial design but as we saw above external political influence delayed BB-55 to FY38 so in the end only BB-56 repeated it’s design (still for FY38). For FY39 two units with a fresh design, BB-57 and BB-58 were authorized in April ’38. The design for them started right after the Japanese cancellation of the treaties, in March 1937 and were finalized in July 1938 (contract designs were done already by December ’38).
However due to the worsening international naval situation Congress was in favor of adding two more of the same, 35.000t hulls to the program, so BB-59 and BB-60 got their seal of approval in June 1938 – although the tonnage escalator clause would have allowed for bigger ships by this time.

The question stared at the designers there yet again: what to build?
16″/45 Mark 6 guns and protection against them were one obvious choice (as a direct evolution and improvement over the previous units) and the Preliminary Design branch went down this path first. What the General Board would want was anyone’s guess: do they want the same tactical features as the BB-55 class units, in order to allow common operation or do they settle for a slower speed design to enhance protection even further? Or maybe they even want to retain the 14″/356mm guns and have a very fast ship? At this point the BB-55 class still bore the smaller gun as well so this was not entirely ruled out.
Additionally there has been a new threat discovered just recently: the so-called “diving shells”. This phenomenon meant that in some cases armor piercing shells falling short of the target could retain enough velocity to travel under water on a level trajectory and penetrate the hull below it’s main armor belt, entering magazines through there.* It was too late to sufficiently modify the two North Carolinas on the building ways so it remained for the new design to offer an answer to this new menace.

*Note:The Japanese have discovered this first in the early 1920s with tests done on the Washington Treaty exiled, half completed Tosa. They took it so seriously that all their modern AP shells had longer delay fuzes to allow for the slower, underwater terminal-trajectory. They have also incorporated protection against these in their latest Yamato class (see there).

In the end the General Board wanted a 27 knot ship with protection between roughly 20-30.000 yards against the 2240 pound shell (18.2-27.4km; 1016kg) and the best possible main battery layout (preferably 9-16″/406mm guns). A brief look at the armor scheme is necessary as it would be duplicated in the next class of ships as well.

Though not directly related, Scheme V of the BB-55 design effort was recalled by Preliminary Design as a benchmark. It had a very short hull (660 feet/201m) to reduce citadel length and concentrated it’s 8 guns into two quadruple turrets, one forward – one aft but it was still only protected versus the 14″/50 conceptual gun. Offering deck protection against the bigger 16″/406mm gun out to 30kyard/27.4km required a deck thickness of 5.9″/150mm, doable on a shortened ship. The inner edge of the immune zone would be more difficult to achieve though, armor would need to be in the range of 14-15″ (356-381mm), quite a step up from the 11.8″/300mm belt on the BB-55 design and a weight that would not fit into the 35.000t limit.

The designers used a solution similar to what the British designer Attwood drew up for the G3 type back in the early 1920s. An internally mounted, steeply sloped belt (19°) and an outer hull with splinter protection to reduce loss of waterplane area (and hull volume). The drawbacks of internal armor were many, including more difficult installation and repair and more limited protected volume. However it had an advantage that came in handy here: due to it’s slope it was deep enough in the hull that it’s downward tapering extension could offer ballistic protection against diving shells and also act as the main torpedo bulkhead.

There were some extravagant solutions proposed for the armor layout, like double sloping belts and even multi-level armor belt/deck combinations but in the end the simple flat deck and single-sloped belt had been adapted.

Still the citadel had to be shortened massively to conserve weight and this made for a cramped ship that gained in hull depth to make up for the lost lengthwise volume. In the final version the 12.2″/310mm sloped belt sat behind a 1.25″/32mm outer plating and together they offered an inner IZ of 18kyards/16.5km versus the Mark 6 gun and the original 2240lb/1016kg AP round.

Torpedo protection appeared similar in logic to the BB-55 setup, with 5 layers altogether. In the previous version it had about equally spaced, similar strength mild steel layers in close to vertical positions with the 4 outer layers being relatively thinner (0.375″-0.625″/9.5-15.8mm) and the 5th, innermost one being the thickest (0.75″/19mm), so called holding bulkhead. There was an additional splinter catcher bulkhead inboard of that.
Here for the BB-57 design the mild steel changed to armor grade special treatment steel layers and bigger room was left for the outer cell thanks to sloping bulkhead positions. Also the 3 outer and the 5th innermost plates were about similar thickness (0.5″-0.875″/12.7-22mm), while the main bulkhead was the 4th one here, being the thickest by far as it was the belt armor’s extension with 5.9″ tapering down to 1.75″ (150-44.5mm ).

Machinery also changed as it had to be compressed to the smallest possible space to keep citadel size, that is surface in need of heavy armor as low as possible. Turbo generators were moved into the combined boiler/turbine rooms so one set of turbines, two boilers and one or two turbo generators made up one machinery unit. Gone were the separate diesel generator rooms both forward of the main machinery units and aft of Barbette #3 – though the aft one was not protected by armor it still helped to reduce overall length.

Combined with some other changes to auxiliary machinery the waterline length came down to only 666 feet/203m from BB-55’s 714’/217.5m. This in turn meant that the hull form became much fatter and to keep Panama compatibility much of the outer hull plating had to be vertical and run parallel. Hull volume was especially at a premium so the superstructure deck was made as long and wide as possible. Only one truncated funnel ventilated the boilers and it got integrated into one massive block of superstructure with the forward firecontrol tower.

This compactness negatively impacted main and secondary gun firing arcs as they already suffered due to being concentrated closer to the ship’s center. What’s worse torpedo protection had somewhat limited depth aside Barbette #1 and #3’s magazines as the hull had to keep a constant curvature to retain it’s hydrodynamic efficiency. The situation was especially bad aft so a fairly genius solution found it’s way: the skegs acting as strength girders and torpedo protection for the propellers were moved from the inner shaft to the outer ones, by simply making those a bit longer. Therefore the ship’s bottom between them could be tapered upwards to satisfy hydrodynamic needs, creating a tunnel where the two inner shafts could be placed. This way the torpedo protection could run as far aft as possible thanks to the ship’s side plating remaining parallel further aft.

Secondary battery mimicked the BB-55 layout as well but this time they sat one level higher to allow a larger deck house. BB-57 was intended to be a fleet flagship, replacing USS Pennsylvania BB-38 in it’s role. Therefore she was to receive a tri-level conning tower – to compensate for this extra weight and volume the middle pair of her twin 5″/38 turrets had to be omitted, making it the only modern US Navy BB with 16 secondary guns only. The 3 repeat ships all had a normal bi-level CT.

Again in contrast to the previous class the Navy contracted 3 of these 4 units out to private shipyards with BB-57 going to New York Shipbuilding & DD Co., BB-58 to Newport News SB&DD Co. and BB-59 to Bethlehem Steel SY in Quincy. BB-60 was the only one built by the public naval shipyard in Norfolk. The reason for this distribution was twofold. The private sector lobby wanted their share of the pie for constructing these expensive units while the Navy and especially the President and Congress were happy to get hulls into the water ASAP. They were not disappointed as these ships were built with record pace, USS Indiana BB-58 completing in less than 30 month from keel-laying. This class was essential in bolstering the numbers in the dark days of 1942, giving the USN modern front line units in place of the old ladies damaged/lost at Pearl Harbor.

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End of Part 1.

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