Montana class genesis – reloaded! Part 2.: Preliminary Design

The Iowa class (BB-61)

Our story gets really to the point from here as the ultimate heavy battleship concept that morphed into the Montana class started it’s development cycle right here, at the same time with the fast battleship.

As we saw above the first pair of new construction ships acted like a working prototype while the second group tried to improve on their greatest shortcoming, which was proper armor protection against the now legal 16″/406mm guns. However only so much could be achieved on 35.000 tons and even the BB-57 class units were not without their compromises.

The tonnage escalator clause in March of 1938 turned out to be a big deal though. The additional 10.000 tons on top of the previous limit meant a lot more capability could be added. And as the kind reader could have already guessed there were two obvious routes again: a ship with massive protection and firepower or a very fast ship with moderate protection and somewhat less firepower. The former became the BB-65 design while the latter the BB-61 in the end.

In fact the tonnage escalator clause would have allowed for BB-59 and BB-60 to be built to a new, enlarged design, but Roosevelt again was cautious and in fairness the plans were not ready yet when those two were ordered. What’s more changing the contracts for private yard ships would have been extremely expensive and reordering material would undoubtedly have delayed construction.

To make up lost ground authorization and order for BB-61 and BB-62 were pushed through very quickly and they were officially contracted for on the 1st July 1939, to be included in FY40. Both contracts went to public Navy yards, to New York and Philadelphia respectively as those builders have had the two BB-55 class units well advanced by now. Focus could shift onto the new bigger ships with them being laid on the second big slipways right next to each of one North Carolinas in both yards.
A year later, to match the number of Kongo class ships and to have some reserve two more repeat units, BB-63 and BB-64 were respectively ordered in June 1940 (for FY41) from the same two Navy yards, getting laid onto slipways formerly occupied by the North Carolinas (now both launched).
BB-65 was intended to return to the classic heavy style american battleship, or so it was thought, and planning for that proceeded under that hull number ID for quite some time. Progress of the war in Europe however changed plans and an unprecedented fleet expansion plan was authorized by Congress after the fall of France. This meant among others that two more slightly modified repeat BB-61 hulls, BB-65 and BB-66 got contracted for in July 1940. Philadelphia NY took up 65 (planned to be laid onto the slipway used by New Jersey after it’s launch) and the Norfolk Navy Yard was assigned number 66 who’s hull actually got laid on Alabama’s launchway.

As early as November 1937 news about oversized Japanese battleships ‘soon to be laid down’ began to circulate. The rumor told about 44-46.000 ton ships armed with at least 16″/406mm guns, however some sources cited even 18″/457mm guns. On the other hand the threat of the fast Kongo class battlecruisers and the even faster Japanese ‘A’ Type or heavy cruisers still loomed over the US fleet and there was no ship in their inventory that could over-match any of these threats on a one-on-one basis.

To combat them 4 major designs have been looked at during Jan-Feb 1938. The first variant from January (labelled ‘8in‘) was a true cruiser-killer, with a 35,5 knot top speed and protection based on heavy cruiser practice, meaning armor was to keep out 8″/203mm shells only, between 10-30kyards (9.1-27.4 km) though. The main armament that consisted of 16″/50 guns arranged into 4 triple turrets was inherited from the concurrent heavy/slow battleship design. In addition there was the usual 5″/38 battery of 10 twin mounts. The only limit on this sub-series was the Panamax beam of 108 feet (33m), therefore this resulted in an extremely long and narrow hull with an unprecedented machinery output of 285.000 SHP. Not surprisingly the ship displaced almost 51.000 tons standard. Alternatively to bring up protection to BB-57 levels (vs 16″ at 20-30kyards /406mm 18.2-27.4 km) Scheme A of Feb ’38 had a somewhat shorter hull with less SHP -still it could make 32.5 knots. Secondary armament was changed to 6 mounts of twin 6″/53 DP capable guns. Standard displacement rose to a staggering 59.060 tons! Scheme ‘B’ (32.5 kn) and ‘C’ (35 kn) wanted to reduce tonnage by removing one triple turret from aft making them 9 gun variants, but even the slower ‘B’ came out at 52.700 tons standard. It appeared high-speed is still prohibitively expensive in terms of tonnage. Perhaps scaling up a smaller design would be better – which is exactly what followed .

Fast cruiser killer, labelled ‘8″‘

Calculations showed that a lengthened South Dakota with extra machinery in an 800 foot (243m) hull could do about 33 knots on roughly 220.000 SHP and yet displaced only about 40.000 tons. Pretty promising, even if this meant giving up both main and secondary battery firepower. Detailed work starting in March-April soon added back weight as more freeboard and heavier (50 cal length) guns returned gradually (again 4 variants have been drawn up). Freeboard was desirable in a long, fast ship to make it seaworthy (otherwise it would pierce through waves instead of riding them). Also advocates of heavier firepower had to be satisfied: the Mark 4 16″/56 gun and even it’s 18″ alternative was briefly considered or let’s say desired, but it was simply too heavy (only 6-7 would fit on 45.000 tons while keeping 33 kn). In the end the Mark 2 16″/50 gun was chosen. It made sense from an economical perspective as well, since many guns originally manufactured for the 1916 program were laying around in storage. Critics from within the Navy brought up that the extra 10.000 tons over the BB-57 only bought 6 knots more speed and nothing else, so this more powerful gun had to be worked in somehow. To compensate for the extra weight the hull form was refined, it was made a bit deeper but shorter and this allowed for relaxing SHP needs a bit. The bow was made narrower reducing resistance but also buoyancy while most of the weights had to be moved aft within the hull to better align the center of gravity with the center of buoyancy. Also the North Carolina type inner skegs made a return, making for a somewhat sleeker stern as well. All in all the new form made up an essentially short hull design with a hydrodynamic extension to achieve high speeds.
Still the design came out overweight at around 46,500 tons. The only saving grace would be a lighter, somewhat more compact mounting and turret design for the Mk 2. guns. However this decision resulted in a blunder not often advertised.

As of April 1938 BuOrd submitted 6 characteristics (weight, dimensions, bore separation, barbette dia. etc.) for triple 16″ turrets:

  • ‘A’ for the 16″/45 Mark 6 gun, basically identical to what was used in BB55/57 classes
  • ‘B’ for the 16″/50 Mark 2 gun with 39’4″ barbette diameter
  • ‘C’ same but with a dia. reduced to 37’3″
  • ‘D’ for the 16″/50 Mark 7 with 37’3″
  • ‘E’ same but with a slide that would allow interchangeability with the Mark 2 gun
  • ‘F’ extreme lightweight option for the 50 cal guns with only a single projectile flat (instead of two as in all previous versions) – submitted later only on 26 May

Due to lack of communication and administrative issues BuOrd went on to developed in detail it’s preferred option, the advanced turret for the Mk 2 gun with a 39’4″ (11.8m) barbette diameter. Designated “B”, this design incorporate a lot of requested modern features (advanced ammo handling, more powerful machinery for faster training and elevation of guns etc.) . However it would NOT fit into the 37’3″ (11.35m) barbettes designed by C&R (BuShips) who calculated with the type “C” turret!! This lightweight option omitted most of the advanced features but was preferential from C&R’s perspective thanks to it’s smaller dimensions.
This was not realized until November 1938, after everything has fully been drawn!
Mating the turret to the hull would have required a wider barbette that in turn needed more beam to accommodate it. This could have been achieved only by extensive bulging or extending the beam forward, leading to a loss of speed (down to 31knots). This would be tragic as the better part of 10.000 tons had been spent to get the highest possible speed.
An other solution would have been to reduce or even omit the torpedo defense system or some of the armor, especially abeam the two forward barbettes. This was even worse, since these units were intended to be the premier capital ships of the US Navy with heavy reliance on their high speed to boot. Finally reverting back to the Mark 6 gun was also disliked.

Worse was the fact that even going by the light Mk 7 guns meant an increase of several hundred tons over the treaty limit, not to mention the option with the Mk 2 weapons.

Very fortunately BuOrd managed to come up with a solution that in the end was relatively pain free and yielded a fairly compact turret. By using the new Mark 7 guns that had a breech-end diameter of only 49 inches versus the Mark 2’s 56.5 inch they managed to squeeze three barrels into the allowed 37’3″ diameter with giving up only better accessibility and ease of maintenance to certain parts. So in the end the smaller physical size rather than it’s lighter weight plus it’s increased availability (thanks to new manufacturing capacity) were the deciding factor in favor of the new gun.

The Mark 2 gun was discarded immediately after this and for good this time. The project was saved at the last minute and meant some major restructuring of the Navy’s design offices afterwards – plus the whole fiasco highlighted how tight even this new, 45.000 limit really was.

There was a price to be paid, of course. The Mark 7 gun and it’s ammo was probably originally intended to first equip the BB-65 series where matching protection could be provided (by using a slower ship with less machinery weight and more armor). Since the BB-61 essentially duplicated the BB-57 armor scheme with relatively minor changes (thicker outer hull plates, minimally thicker main deck and main bulkheads) it already suffered a reduction in IZ when the switch to 50 cal. length guns happened: from the original 18.000-30.000 yards it shrank to 21.700-32.100. Introducing the Mk 8 super heavy shell brought this down to 23.600-27.400 yards (20.200-25.500 vs the older, shorter gun with the same shell), uncomfortably small for an otherwise high-end battleship. Truth to be told this really showed the enormous firepower of the new gun and shell combo instead the lack of armor on these ships – in fact the Mk 8 AP shell was retrofitted to both the BB-55 and BB-57 units as well, giving them a punch way above their weight class.

As detail design progressed from late 1938 some more changes were made to make the BB-61 type more survivable. By Nov 1939 the 4 huge machinery spaces (that duplicated the BB-57 layout but with much larger room sizes to accommodate the bigger boilers) got further divided into 8 rooms. Auxiliary machinery with a pair of boilers placed side-by-side moved into a separate block and turbines into the other half of a former unit machinery space, thus reducing flooding by half in case of a hit directly on a bulkhead. This was suggested by the New York NY, building the lead unit and doing the detail design.

Final machinery arrangement adopted for BB-61 class

On the ballistic protection side of things a second or extended armor belt of 13.5″ thickness had been added aft as well, to cover steering leads in the somewhat longer aft section of the ship. Main turret face plates went from 17″ to 18.25″ effective, while forward main armored bulkheads grew from 11.3″ to 14.5″. This latter change could only be applied to hulls BB-63-66 since armor had already been ordered for the first pair. Fortunately all the ships were assigned to public navy yards, therefore the changes did not cause delay nor extra cost, only added some weight.

The torpedo defense system entirely duplicated the BB-57 layout, except at the stern, where the revised skeg setup meant a return to the underwater hullform of BB-55. Tests showed this system to perform worse than expected and a somewhat modified version was planned for the last pair of the class.

All these modifications have added considerable weight, but by late 1939 the already ongoing war meant the complete abolishment of treaty limitations.

The Montana class (BB-67)

Montana class general overview:

The Montanas were the last and final battleship class designed for the United States Navy with design process starting in parallel to the BB-61 Iowa class. The fast 45.000 tonner, described above, took priority as it was preferred by many in the navy. Also trustworthy information on foreign ships were scarce and it was thought that the BB-61 class ships would be equal if not better to anything under construction. Still in the background work went on to create a new “standard” type of battleship which was not so fast but had the best possible armor protection with maximum firepower. As the design progression took well beyond 1939 it had two distinct phases, the BB-65 series and the BB-67 one. The first one was still limited to 45.000 tons and was intended to be built following the first four Iowas, hence the hull number. With treaty limitations going away however a fresh set of plans investigated all possibilities, including extreme dimensions, but these still ran under the BB-65 moniker.
Only after the passing of the Two-Ocean Navy act did final design start, now under the BB-67 designator as it was the first hull ordered to the new battleship design.

Early ‘slow’ 45.000 ton designs

The slow version of the 45.000 t battleship started out it’s cycle in very late ’37/Jan 1938 to investigate how the possible escalator clause on tonnage could be best used. Essentially the designers added a 4th triple 16″/45 Mark 6 turret to the BB-57 design: length grew to 770′ on the waterline. Armor was changed a bit (thinner belt but heaver decks, turrets and splinter protection) so the IZ was 20-30kyards against the Mark 6 gun with the normal shell. Propulsion was increased to 170.000 SHP to maintain 27 knots. The design reflected the original BB-57 in retaining only 16 of the secondary 5″/38 guns.
For a time focus shifted to fast designs as described above, however in April and June 1938 further studies were made to evaluate gun options for the future main type of battleship, as the fast variant looked like a one-off design at that time. The April 1938 (I) version offered 9-18″/48 guns in three triple turrets with a full suit of 20 secondaries , all this on a 800′ long hull, still limited to the Panamax beam of 108′. Draft however rose to 36′ from 35′. The longer hull allowed for 27 knots with the original 130.000 SHP plant. The omission of a 4th turret and barbette translated into more vertical armor (14.75″ belt, 20″ turrets and 21″ barbettes), with a respectable 20-29kyards IZ against it’s own gun, with the original 2900# AP shell. Splinter protection and deck armor remained the same though. Essentially this design reflected the logic and relation to the 35.000 ton limit behind the BB-57 design on a bigger scale: to produce a fully protected, balanced 18″ battleship just within the new, 45.000 treaty limit (it actually came out at 45.500tons). It is assumed that more than one version had been drawn up in April but these were possibly either less powerful (only 6-7 guns) or too slow to be relevant (data is missing entirely, but the roman numeral ‘I’ in the designation gives it away). Also as we saw above the more powerful gun had been under consideration for the fast 45.000 tonner as well but there protection and firepower (that is number of guns) had to give to stay within allowances. In fact the 18″ was still illegal under the then prevailing conditions but Capt. Chantry, head of Preliminary Design was convinced that the Japanese are going for the bigger caliber, despite lack of concrete intelligence evidence. Note that this design was generated only a few days after the Japanese announced their withdrawal from any treaty agreements, so it just made sense they will use their extra tonnage to massively improve firepower. As we know today Chantry was more than right.

Slow battleship Design April 1938 (I) with nine 18″/48 guns

In June 1938 the original, 12-16″ concept was upgraded to /50 cal guns with protection again replicating that of the BB-57. This was done as a feasibility study to ascertain if a well protected (against the normal shell) 12 gun 16″ battleship is indeed possible on the new 45.000 tons limit, without giving up much speed. Several different length hull shapes have been investigated, from 755′ up to over 800’+. Model tests showed that the optimal length from a wave making resistance and power to hull weight ratio aspect lay around 810′. Therefore two variants ensued from these with the full 20 secondary guns: one with the minimum required length of 785′ for the four turret arrangement combined with the max. allowed draft of 36′; and the other with the 800′ hull. The former required 130.000 SHP, the larger one only 115.000 SHP to reach a top speed of 27 knots. Extra large hulls already started to pose an issue for the slipways at New York NY as those needed modifications that is why the shorter version made sense at all.

Design Studies of July-September 1939

For over a year the focus of the Preliminary Design branch went back to the fast battleship and to other major, non-battleship related projects. The Bureau of Ordnance however introduced and actively worked on several new weapons in the meantime, the most important being the Mark 7 16″/50 gun and it’s associated Mark 8 super-heavy armor piercing ammunition. Moreover a powerful medium caliber gun, the 5.4″/48 Mark 1 was in development as well, to arm new generation cruisers and destroyers. It had also been contemplated as secondary battery option for the new battleships. Besides the Mark 1, an up-rated 5″/38 (12.7 cm), a new 5″/54 (12.7 cm) and an improved 6″/47 (15.2 cm) were in the pipeline as alternatives. The 6″ have had dual purpose capability and somewhat later automatic loading envisaged for it. These weapons allowed for precise fire at longer ranges (18.000 yards surface and 14.000 yards slant/AA mode for the 5.4″/48 Mark 1) and offered much bigger stopping power thanks to their heavier shells. The 5″ variants had a 75 pound shell (compared to the existing Mark 12 ‘s 56#) and the 6″ could use a 130# AP ammo against surface targets.

The massively increased mounting weight of the Mark 1 convinced BuOrd that it would not offer the desired improvement overall, since only 5-6 twin mounts could be had in place of the existing 10 mount 5″/38 battery. The more numerous barrels and higher rate of fire would more than compensate for the individually lighter shells, especially in AA mode. Therefore in January 1940 the 5″/54 was selected for further development as it could use the mounting of the 5″/38 Mark 12 while still keeping the heavier ammo. This gun became the 5″/54 Mark 16 but in the end armed only the CVB-41 Midway class carriers (and ironically some post-war Japanese DDs). The 6″ weapon represented an entirely different category in hitting power so it got it’s lease of life as well under the 6″/47 DP Mark 16 designation. Unfortunately it’s development took much longer than expected and entered service in 1947 only, arming the CL-144 Worcester class cruisers.

July 1939 saw design work picking up again when the General Board requested twelve gun 45k tonners from C&R that offered protection versus the 2700# Mk.8 shell. Speed requirement was set at 27 knots to match battleline speed with previous ‘slow’ classes (BB-55 and BB-57).
Design BB65A opened the line, basically duplicating the 800 foot June 1938 version with power increased back to 130.000 SHP. Dimensions (800′ x 108′), power (130k SHP) and speed (27kn) remained constant for the entire 1939 series, only armament and protection varied. This baseline variant offered complete (18-30kyard) protection versus the Mk 6 gun/2250# shell combo only, essentially BB-61 level of protection. It came in at 45.400 tons.
For comparison it is worthy to note that the IZ vs the Mk 6 gun/2700# shell combo would be 20.500-26.500 yards only. To raise this back to the original 18-30k yard on this layout would have cost 47.800 tons, well over the treaty limit.
BB65B used an alternative secondary battery of 6 twin 6″/47 turrets, otherwise duplicating 65A (being concurrent). It displaced 45.600 tons. To bring up the secondary battery to 20 barrels (10 twin mounts) would again add a direct weight of ~500 tons plus about 1000 tons in ship and armor weight, equaling a total of ~47.100 tons.
It was getting clear early on that buying proper protection and/or improved secondaries won’t come cheap in weight terms.

The General Board directed C&R to try using quadruple turrets to save weight, just as they did with the BB-55 preliminary designs when going for the original twelve 14″ gun armament to fit into the then ruling 35.000 tons limit. The resulting
BB65C simply used three quadruple turrets, two forward and one aft, mated to a BB 65A hull. The net saving was 800 tons, with an other 800-900t coming off of turret/barbette armor and hull, making for a very nice 43.800 tons total. This encouraged to try for heavier armor using up the remaining 1200t.

BB65C, all quad turrets

BB65D came before that however, it simply acted as an alternative to 65C with the secondary battery switched to 6 twin 6″/47s, increasing displacement to a round 44.000 tons.
BB65E tried to answer the extra armor request made possible with the all-quad turret setup. The heavy shell really had it’s extra penetrating power at outer ranges, therefore bringing in the IZ to 18-26kyards by using the Mark 6 gun as a reference seemed feasible on 44.800 tons. This meant that the extra weight mostly went into vertical protection (belt 13.2″ from 12.1″) while main deck remained the same and the reduction in the outer IZ had to be swallowed. She had the classic 20-5″/38 secondary battery.

The quad turret looked really obvious and tempting on paper but several factors mitigated against using it:

  • it’s rotating weight exceeded 2000 tons
  • it required a pretty huge cutout in a beam limited hull, especially forward where it narrowed and two barbettes sat close together – reducing hull strength and putting enormous moving weights into the most sensitive spot
  • due to it’s sheer size it required more powerful motors for turning and one more set of gun-elevating drivers per turret, meaning that total electrical generating capacity needs went up to 10MW (from 7) – this in turn required more machine room length that had to be protected and this added direct weight

The alternative solution to cut weight would be a return to 9 guns, or more precisely 3 triple turrets.
BB65F acted as a baseline concept for these with essentially being a 16″/50 equipped copy of BB-57 of course on the BB65A hull. It had BB-57/61 protection and the full 20 gun secondary suit but even with that it came in at only 41.600 tons, lightest in the entire Montana class preliminary design history.
BB65G acted as the really desired step, with armor against the heavy shell. The belt at 15.4″ proof at 18kyards against the Mark 7 gun and the main deck with 6.2″ safe out to 30kyards against the Mark 6 guns. In other words full protection against the more dangerous weapons at their respective rangebands. What’s more it displaced only 44.600t!
BB65H and BB65I trimmed the weight down even further, by offering full protection (18-30kyards) separately against the Mark 6 and Mark 7 guns respectively. They dispensed with the mixed threat, and therefore could save an additional ~200t each, otherwise they duplicated 65G.

A third, absolutely undesirable solution to remain within the treaty limits proved to be the reduction of gun caliber.
BB65J sorely relied on four 14″/50 triple turrets with an almost complete (20-30kyard) protection against the Mark 7 gun and the heavy shell, all this on 44.380 tons. Simply four turrets and their barbettes weighted an awful lot with the level of protection required against this extremely powerful weapon and shell combination.

BB65A to J. Color coding represents grouping by design logic. Data for C2 and C3 are confusing in several sources, therefore the actual armor thicknesses are extrapolated from the other designs

Not surprisingly the General Board wasn’t pleased with any of the 9-gun or the 14″ variants, no matter how good their protection was. If the BB-61 fast designs on the other branch spent all the 10.000 tons of extra on speed then these did the same on armor protection. Something in the middle would be more desirable.
Many within the navy pushed for extra firepower over the previous classes as that was what really mattered in a battleship – so they argued. To reach that extra superiority the good old Mark 4 16″/56 or even some 18″ers were suggested (at this point the re-conversion of the Mark 4 to 18″ was a plan only). General preference was still for twelve 16″/50s, if possible in triple turrets.
Captain Chantry knew that this would be impossible on 45.000 tons with proper armor as the previous designs proved. He suspected though that 10 or maybe 11 guns could work combining twin or triple turrets with the quad. They took BB65C, the one with three quads and started to tinker with the armament and armor as follows:

BB65C-1 tried to gain some space for torpedo defense in the forward hull, therefore it went with a mixed quad-triple-quad turret layout with shortening the citadel and resulting in a fairly unique 11 gun setup. It became the lightest from all ‘C’ variants at only 43.500t. Protection replicated the vanilla BB65C.


BB65C-2 answered a new armoring requirement while retaining BB65C’s all quadruple turret layout. It took the 2700# pound AP shell as it’s basis and used the best belt penetrator gun, the 16″/56 Mark 4 (as it was proposed above) for the inner edge of the IZ and the best deck penetrator, the 16″/45 Mark 6 for the outer. Added extra belt and deck thickness gave an IZ of 21-27.000 yards (armor thicknesses aren’t quantified correctly -if at all- in the sources, but total tonnage grew to 46.100t compared to 43.800t in BB65C and extrapolation from the other designs stats give a belt around 15.4″ with a 5.1″ deck) .
BB65C-3 simply merged C2’s armor to the C1’s turret arrangement, bringing down displacement very close to the limit at 45.100t.
BB65C-4 trimmed back protection of C3 slightly, to get under 45.000 tons. The resulting IZ offered protection versus the heavy shell in the 19-27.8kyards band against the Mark 7 gun at both ends, or alternatively 22-26kyards if matched against the Mark 4/Mark 6 gun combination as above.
BB65C-5 and BB65C-6 brought the above line further by reducing main battery to 10 barrels in a quad-twin-quad and triple-triple-quad (aft) arrangement respectively. Armor protection now matched that of BB65J, with the 16″/50 Mark 7 taken as a basis firing the heavy shell. C-5 would have required developing yet one additional turret (the twin), so from a practical and economical point of view it was a dead end.


It became fairly clear that even the extended treaty limit is very tight. Furthermore the 108 foot beam limit due to the Panama Canal lock’s restricted options on armament choice and layout.
The main gun of choice had mostly been decided as well during this period. The 18″ rifle still came up periodically (even as late as July 1940) and was favored by quite some (including Chantry), therefore the re-conversion of the Mark 4 was proposed and later funded, but it came too late for the BB65 design. For the time being the 18″ was held back for political reasons as well and reserved for a time when one of the probable enemies apply the same.
On the other hand the July series clearly showed the firepower boost that the 2700# AP shell brought to the table, seriously increasing penetration capabilities even for the older, shorter Mark 6 gun. In fact there was little point to press for the 18″ gun without it’s heavy shell when similar performance could be had while more guns could fit into a given displacement limit (only 6-7 if protection is kept at the same level). And this very factor finally doomed any 18″ hopes for the Montana class.

Captain Chantry and the General Board both favored BB65C-6 as a good middle ground option from the whole series. With two triples forward issues of torpedo defense system depth and hull strength were gone. Optimally if one wanted the quad turret it had to be placed aft: the widest part of the hull offered the best buoyancy and extra stiffening was provided by the skeg layout when in drydock. By September more precise weight data was available so it was deemed to worth a try for further development and several sub-variants got sketched with 5.4″ secondary guns (with 8-10 twin mounts). This point marked the end of the first stage in the Montana class preliminary design process.

Preliminary design Stage II: January-February and March-July 1940

The outbrake of WWII had two major impacts on the Montana class design progress, both concerning the size of these ships. First, with France and the United Kingdom getting actively involved in the conflict from day 1, they naturally cancelled their Treaty obligations, meaning that the 45.000 tons/16″ gun limit belonged to the past from now on. Ironically the gun question has more or less been decided by 15th September (just when the 18″ gun could have had a chance) when the General Board held it’s meeting to decide on final characteristics for the BB-65 class: it remained only to choose between using triple or quad turrets (or their mix) to get the desired 12 gun ship. C&R really disliked the quads and they weren’t generally popular. An other aspect that probably weighed-in against the quad turret and the 18″ was the speed of production, now that there was a shooting war where the US might get involved called for using as much existing technology as possible. By mid October 1939 the General Board already made the commitment to using triple turrets only. They have asked C&R for two new versions, both unlimited in displacement but still with a Panama compatible 108′ beam: one for 27.5 kn (replicating the BB-57 powerplant and it’s 130k SHP) the other for 32.5kn (replicating the BB-61 powerplant with 212k SHP), to match previous classes. Both were to have four triple turrets with Mark 7 guns and a full suit (10 mounts) of the old venerable 5″/38s. No detail work was done but they were expected to displace 50 and 55.000 tons respectively.
The second new factor that massively changed the upcoming designs was the prospect of a new set of locks for the Panama Canal. It was on the agenda for quite some time together with new ship building facilities, especially graving docks (at least from April 1938 onwards) as the new generation of capital ships were severely handicapped by this practical but now elderly rule. By late 1939 a new set of locks, at least 130 but preferably 140 feet wide were proposed, along with a massive expansion of some navy yard’s docks with special focus on New York Navy Yard. The General Board specified dimensions up to 1000′ waterline length by 130 foot beam and with a possible draft of 36, 38 or even 40 feet, with damaged draught reaching 43′! Most of these expansions got funding and approval from relevant authorities, so it finally appeared to C&R that they can work without any restrictions, for the first time in many years.

January 1940 saw the Preliminary Design branch hard at work again, incorporating the above developments into their proposals. The removal of beam restriction especially opened up possibilities and offered more balanced designs (previously the ships had to grow in the vertical plane with ever higher and more robust superstructures combined with deeper draught – both are very evident on the South Dakota and Iowa classes). If one looks closely it is obvious that this whole January-July 1940 period offered a selection of almost all the earlier ideas from the whole design progression rehashed in a much improved form. One gets the feeling that reaching a consensus on what to build was not coming easily this time.

For ease of understanding I’ll list the designs below based on logical (and quite probably sequential) order instead of numerical order reflected in the names. In addition it is worth to note that three distinct groups can be observed among the list, all were running mostly parallel as different train of thoughts:

  • first, BB65-1 to -5 were medium sized (relatively speaking) with characteristics resembling closely of the previous design cycle. These all used existing power plants to simplify design work: either the 130.000 SHP of the South Dakota (BB-57) class, the 212.000 SHP plant of the concurrent fast ship, the Iowa (BB-61) class or an intermediate option, a 150.000 SHP plant combining two sets of 75.000 SHP Atlanta (CL-51) class light cruiser machinery
  • group two, BB-Yx and BB65-6 to -8x variants were brand new in that they combined the heavy battleship with high speed and very good armor protection. These either used the Iowa plant or some more exotic, custom types matched to the required power output
  • the final group, added only in the follow-up design cycle of March-July 1940, again tried to cut back size and costs to a more reasonable level. Obviously they used the same plants as the first group

To address the General Board’s request from the previous October, now without the Panamax restriction Preliminary Design offered two slow, 27 knot designs first.

BB65-3 was the baseline, offering an IZ of 20-30kyards versus the heavy shell fired from the Mark 7 gun (standard for all from here). The armor resembled the BB65-C5 and C6 series from the previous design cycle with a 14.2″ belt and 5.5″ deck which as we saw was preferred by Captain Chantry and team. Beam however increased to 114′, no reasons given. The bigger hull probably offered much better torpedo protection as well, although there is little evidence about it’s exact layout (quite probably it repeated the previous two class at this point). The armor scheme resembled that of the earlier ships as well, with an internally mounted, 19° sloped belt and a 1.5″ (60#) outer hull plating. The South Dakota plant could drive this ship at 27.5 knots.

The baseline BB65-3 February variant, reconstructed from Spring Style sketch

BB65-4 added the new Mark 16 secondaries to the above variant of -3, and had an extra 30′ length to compensate for the added weights (2000 t extra for the heavier secondary battery). There were 10 twin mounts arranged in either to South Dakota/Iowa layout (two mounts on 01 superstructure level and three on 02) or the North Carolina scheme (three mounts on the main deck and two mounts on 01 level). Otherwise it was duplicating BB65-3.

BB65-4 as of Feb 1940, extra length added in the middle to maintain speed; note the alternative secondary battery layout

Concurrent with these slow versions they tried to satisfy the General Board request for a 32,5 knot ship as well and the following concepts ensued:

BB-Y2 optimistically took the Iowa plant and the armor and armament of the above BB-65-4 but even with a very long, 1000 foot hull it could only do 31.75 knots. Beam was up one foot at 115′.
BB-Y1 calculated with a theoretical plant, to reach the desired 33 knots with the hull of -Y2: a staggering 318.000 SHP would be needed, adding two more shafts for a total of six since existing blade design allowed for a maximum of 50.000 SHP per shaft only
BB-Y3 calculated with a refined hull, somewhat reduced in weight (no details given) to be driven at 34+ knots with the same theoretical 318.000 SHP powerplant

The next step was to increase protection along the lines of BB65-G of the previous cycle offering alternatives to the above designs that otherwise mirrored them in almost every other aspect.

BB65-1 opened the new, slow line by taking the BB-65-3 and increasing the belt to 15.3″ while the deck remained the same, resulting in an IZ of 18-30kyard. Secondary battery consisted of the usual 20-5″/38 Mark 12s. Fittings appear to be much heavier (2100t vs 1800t on -3) and protection lighter despite the heavier belt, but despite this actual displacement was 200 tons lower than the baseline variant thanks to one foot less beam. It is possible that the armor is counted in a bit different way here or that some unmarked weight saving changes were introduced.

BB65-2 added back the new secondary battery, with the new 5″/54 Mark 16 taking the place of the former Mark 1 5.4″ gun as a good compromise between gun performance and weight . The bigger guns again increased displacement by about 2.000 tons in total, requiring a somewhat longer (860′) hull. This had the positive effect of reducing draught to 34.5′ only. Otherwise it replicated -1. Basically the ultimate version of the previous design cycle, not capped by the treaty limit of 45.000 tons now.

BB65-5 expanded the baseline concept the farthest with the IZ now extended at the outer edge as well. Total protection now covered 18.000-32.000 yards, that meant a heavy, 6.2″ main armor deck was mated to the 15.3″ belt of the BB65-1. The Mark 16 secondary guns were also added in for good measure. To cope with the extra weight waterline length grew to 900 feet and displacement rose to 56.600 tons standard! Exact data is missing about the speed and power figures, but probably it had the same 130k SHP plant as the previous versions and speed fell to 27 knots or the 150.000 plant was added in to maintain 27.5kn. This variant resembled first the finally selected one and was developed from this.

BB65-6 addressed the fast line, a well protected and fully armed design, so it entered the 60.000 tons+ category. It used the same protection and armament (both primary and secondary) as BB65-5 but added the BB-61 class powerplant of 212.000 SHP from BB-Y2 essentially being the up-armored, more condensed version of that. Speed accordingly fell to 31 knots from 31.75 but IZ was 18-32kyards in return.

BB65-6 Feb 1940; artistic recreation based on know variants

BB65-7 became the distilled variant of BB-Y1 with a powerplant of 320.000 SHP (probably four Atlanta class sets overdriven). It still retained the thinner, 14.2″ belt and corresponding IZ of the original Y variant.

BB65-8 went all in and added the heavy protection of BB65-5/-6 to a very long hull resulting in the largest ever seriously contemplated US Navy battleship design, with a 66.000+ tons standard displacement. Length grew to 1050′ and beam an additional foot again to 116′. At least four sub-versions were made, we know BB65-8D dated as 23rd Feb 1940. The difference quite probably lay in hull design/contour and layout. 8C had it’s length increased to 1100′, while 8D had less horsepower (293.000 SHP). Unfortunately details are very hazy and difficult to come by but variations might reflect different propulsion technology (turbo electric plant etc.) and wildly different shaft arrangements as again 6 shafts would be a minimum for this level of propelling force.

List of all designs from the period that have known data

To answer the General Board’s request of 16th February the above array of options were consolidated into a new spectrum study, with some renaming/reshuffling done and some new, more or less reduced options entering the list. Again it is very important to note that the nomenclature does not mean any sequential order and some duplication in naming was not refrained from. To make it easier to understand I’ll again go through by logical order instead of numerical one.

Very important that at this point in the design process a fundamental change occurred, namely the switch back to external armor, more akin to what was used on the North Carolina class, thus abandoning the internal belt with the 60# splinter plating on the outer hull. This is reflected on all March designs below. The previous 14.2″ and 15.3″ belts changed to 14.6″ and 15.75″ respectively. What’s more the external belt’s, 19° slope meant that beam was much reduced at and below the waterline. To compensate blisters were added below the waterline and both the waterline beam and the width at the armored deck had to increase, again adding about 700 tons (more in the very long BB65-7 and -8). Even worse was that with this change gone was the armor protection against diving shells – evident on the February designs. However at least by mid-March the BB65-8 sketch shows a secondary lower armor belt, mounted on the innermost torpedo bulkhead so it is likely that the entire March series had this modification. This design element was again reflecting on the BB-55 class ancestors that had a very similar hull cross section. Here the internal belt could be much thicker though.

BB65-8 as of March 1940, the Big Boy of US battleships; note the lower armor belt on the cross section

BB65-3 changed very little apart from the external armor belt. Waterline length increased to 860′ up from 840′ so speed grew to 28 knots thanks to less wave making resistance. Displacement sat at 52.500 tons, quite a long way up from the original 12 gun concepts derived from BB-57 back in 1938. It is notable though that armor protection was much heavier and it also sported the longer guns.

BB65-3 if it had been selected as a final design

BB65-4 had the machinery beefed up to 150.000 SHP, thus it could do 28 knots as well making it the slowest accepted speed for the new designs. Armor belt changed similarly to an external one, otherwise the same as before.

BB65-4, finalised

No major changes were done to BB65-5 to -8 apart from the external armor belt and some length/width added on -6.
SHP is listed as 320.000 for -8 as the final figure, probably reached with a turbo electric drive as no conventional turbine plant was capable of that at the time with 6 shafts included. This is supported by the fact that the sketch design does not show subdivision of machinery spaces and are left blank.

BB65-6; intermediate speed, but full protection and armament in an as built configuration
BB65-8 if would have been built: 33 knots, 12 guns, full protection, what more an Admiral could wish for?

Further options were developed to fill out the spectrum study in addition to the six above mentioned, sort of consolidated versions, that all offered 12 gun ships, both slow and fast ones with either 18-30, 20-30 or 18-32kyards immunity, while secondary battery was exclusively the heavier 5″/54 Mark 16 except for BB65-3.

On the other hand entirely new were BB65-1 and -2 reusing the nomenclature from the previous series. Seeing the explosive growth in size and weight many wondered if a well armored 9-gun ship would be preferable. In other words was the extra turret worth it?

BB65-1 was essentially a beefed-up and stretched Iowa with a little more beam and the heavy protection. It kept the Iowa main/secondary battery and powerplant while the armor was brought up to the new standard 15.75″ belt but only the 5.5″ deck, so IZ was 18-30.000 yards. Speed fell to 31 knots.
BB65-2 further increased length to a massive 980′ in order to maintain speed at 33 knots with the existing Iowa powerplant. Beam also rose by one more foot compared to -1 above.

Available sources are not clear, conflicting and illogical about what followed in the March-July period, but here is a best effort reconstruction that is subject to change once more info becomes available.

Finally, probably in June 1940, after the initial opinions from stakeholders were in, two more options were added:
BB65-9 took the baseline BB65-3 and added the heavy belt, this time beefed to 16.2″ to reflect improvements in the Mark 7 gun’s now improved muzzle speeds. The AD remained at 5.5″ though, so IZ was set at 18-30kyards.
BB65-10 was the corresponding 9 gun variant with a standard displacement of 48.000 tons and much shorter hull (830′) and narrower beam (110′); both of these designs had the older Mark 12 secondary guns and 130.000 SHP for 28 knots only probably to save weight compensating for the even thicker belt. It is also notable that the 5″/38 Mk 12 was preferred for it’s lighter weight and better suitability as an anti-aircraft weapon over the newer, longer barreled Mk 16.

Evaluation, selection and further designs

On 9 July 1940 the General Board and the representatives of the Bureau’s met again to review the designs and a lot of questions were touched upon with the following inputs given:

  • Cpt. Crenshaw (War Plans) favoured the balanced but still powerful BB65-1 as they saw eccentric battle operations a more likely option for future battleship combat instead of the old battleline concepts. They wanted higher than 27 knots speeds (but saw 33 knots excessive in light of foreign construction – still they suggested adding two more 33 knot 45.000 tonner to the building program (which was already on by then with BB-65 and 66 ordered as Iowa class units). They also wanted good protection and the minimum acceptable battery of 9 guns, to keep ship size down. War Plans also pointed out that drafts should be kept to the lowest achievable figure in order for damaged ships to be able to use as many ports and docks as possible and this again pointed into the direction of 9 guns and medium speed
  • Adm. Greenslade (General Board, conducting the hearing) responded: whether to assume this design (BB65-1) to be the prototype of the next 6 battleship to be built or alternatively shall they build 3 slow (28knot) sturdy ships and decide later about the next three – having BB65-5 in his mind
  • Cpt. Crenshaw opinioned against BB65-5, citing that the 3 extra guns and the additional .7″ deck armor did not worth the 8000 tons extra displacement; War Plans preferred BB65-9 as the 12 gun option if absolutely necessary, but was not convinced for the heavier battery even in a slow ship, as it made ship size impractically large for harbors and docks, especially in damaged condition
  • interestingly enough Adm. Greenslade interjected the question if a US 18″ gun would be required in case the Japanese or the Germans build capital ships with that caliber – Cpt. Cooke of War Plans responded that indeed they should provide equal or greater caliber guns as an answer
  • Cpt. Griffin (Fleet Training) added that while they generally agree with War Plans they feel that attaining any objective or operational scenario worth using battlehips would depend on the strength of those ships and not their speed. Furthermore asking 33 knots from battleships when existing cruisers can only do 35 knots at best is rather impractical; Fleet Training felt that BB65-5 is the most desirable option as it offered the greatest fighting power and the best defensive hull with the heavy secondary on a rather economical tonnage
  • Adm. Greenslade asked Fleet Trianing as well on their opinion about possible foreign 18″ guns appearing on ships; FT too justified equal response with reduction in the number of guns and increased protection added
  • Cpt. Washburn of Fleet Maintenance was going next with preference for BB65-5 too, reasoning that a “battleship is supposed to always be able to give and take it”. He added that dimensionally the extra size over BB65-1 preferred by War Plans is in fact marginal and it also had the much more powerful 5″/54 secondary battery
  • Adm. Noyes (Communications Div.) also favored BB65-5 based on the not so great speed deficit compared to lighter ship types
  • Finally Adm. Van Keuren of BuShips added a lot of detail: he highlighted the fact that now they can go as far as they want in terms of ship size since the only practical limit being waterways and drydocks (but the latter would be taken care of). They could even go up to 100.000 tons displacement except that the draft would be out of proportion but a super ship is technically absolutely feasible. He recommended to look at the question from a strategic point of view ie. these ships might be the last they can build and have unlimited money for the coming 20 years so instead of following foreign trend they might want to go the to biggest straightaway and lead the way
  • Adm. Sexton from the General Board asked how far would BuShips recommend to go and the response was at least 12 guns and 40 feet of draft; on explaining the advantages of deeper draft he pointed out that if one dimension of the hull is limited they have to go to the extremes in other things and it would result in sub optimal hull forms (see BB-61 where the beam was limited)
  • Adm Van Keuren suggested that if the 18″ guns are neglected than 12 – 16″ guns, full portection and at least 31 knots speed (BB65-6) is desirable

Almost unilaterally BB65-5 was the preferred choice, in fact the General Board already favored it by March 1940 and therefore asked for a shortened, modified version as BB65-5A that reduced waterline length to 880 feet (from 930) and to compensate for that and keep speed at 28 knots it switched to the Iowa powerplant (212 vs 150k SHP) as the shorter hull had higher wave making resistance.
The reduction in length was needed for a multitude of reasons: it enable the New York Navy Yard to participate in the construction of these ships – it was one of the most important building yards and had two out of five of the new construction docks intended to build these new, heavy battleships (see Part 1). Also a shorter length was preferred from a manuverabilty point of view, both tactically and within port facilities as we saw above.

The hearing went on focusing on powerplant options:

  • Cpt. Irish (BuShips) listed the various powerplant options (130k, 150k, 212k SHP) and their origin (listed above) and added that above that they have to go electric due to technical reasons. This would add weight and space and also would add a lot of development time as a completely new machinery design would be required; they also looked at the option of installing a diesel electric drive where a large number of small, high speed engines would be used driving generators through a control room – this would allow for an even greater subdivision, 25 to 30 compartments in a 320.000 SHP plant, while it would also eliminate huge cutouts for stacks and the loss of power would be more granular in case of underwater damage (ie smaller proportion of the total power lost)
  • COmmander Braine (BuOrd) was asked to offer his department’s views and as expected they suggested going with four turrets, either BB65-5 or BB65-6, depending on the speed requirements; he also added that the 18″ gun is a viable option, being under testing with the 3800 pound projectile so they only awaited the General Board’s call to get a battery based on it ready (36 month approx.); he also elaborated on the amount of armor needed and that the bigger ships (-6/-7/-8) needed a lot more of it while production outpout was currently still limited (see Part 1)
  • The discussion returned to ship size when Cpt. Cooke (War Plans) presented that BB65-6 with it’s 1050′ length might handle well at sea but in harbors, especially in damaged conditions, is an entirely different case; the greater length and beam on these designs meant much more draft if the ship rolls or lists – 900 feet length with 112 feet beam and 36 feet draft is the maximum that could be handled currently
  • Finally Adm. Freeman (General Board) brought up the point of equally distributed main batteries fore and aft and it’s importance (or lack of it) and also the lack of design options with 10 guns arranged in one triple and one twin turret both forward and aft

As we can see by now the very large fast designs (-6/-7/-8), all displacing above 65.000 tons standard fell out of favor as they were both expensive in terms of armor needed, took longer to build and required exotic machinery. And of course only a limited number of shipyards had large enough docks and installations to service them.

Also as we saw many again questioned the value of a 4th triple turret, requiring 10-15% extra displacement – especially now in light of the need to have ships in the water at the earliest. The later CNO, Admiral King (also present at this hearing) was an outspoken opponent of the huge, 12 gun designs.

Therefore sometime in mid/late July even more sketch designs came out of C&R:

Two unnamed, uncompleted 10 gun options answered Adm. Freeman’s call and offered an intermediate choice between 12 and 9 gun ships. Both used a Nevada class style arrangement of triple-twin-twin-triple turrets. One of the two designs being Panamax. They were dropped even before done as uncompetitive (marginal reduction in weight compared to 12 gun ships with substantially less firepower).

As suggested by War Plans focus now shifted for 9 gun versions to have the smallest possible, but fully protected battleship.

BB65-11 and 11A further developed the 9 gun BB65-1 with bumping up the secondaries to the Mk 16 gun and reducing length to a more reasonable 860′ but increasing the beam a bit to 112′. Protection was also increased to the latest standard, with an IZ of 18-32kyards. As a result speed fell further to 28 knots only. Power was the medium option of 150k SHP for -11 while 11A traded length for power (212k SHP but only 820′ length).

BB65-12 was advancing BB65-2 , protection remained the same but the heavier secondaries made their appearance here as well. Length was cut back to 950′ so the Iowa powerplant was good for 32 knots only.

BB65-13 finally took the actual BB-61 final design, upgraded the secondaries and the armor to the full option and lived on with the speed reduced to 28 knots. This in fact was a super-Iowa with a hull form filled out but still Panamax compliant. Adm. King personally pushed for this version to be included in the range of options.

March-July period designs; note that -1 and -2 are different compaerd to Jan-Feb

While all this design work was going on in the offices war has progressed to a point where it started to have a direct impact on proceedings.
France surrendered in late June and the German air offensive against Great Britain was about to start in two weeks time. There was a good chance that Great Britain will fall as well then the United States had to fight Germany and Japan alone on both oceans.
To mitigate this the “Two-Ocean Navy” act (detailed above) was put in effect by Congress that would authorize the building of insane amount of ships – and the design for the crown jewel, a heavy battleship was badly needed.

End of Part II.



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