If they have the 5/38 why would they want to put the M3 90 mm gun on their ships?
Didnt some US ships have old 3 inch guns? or at least for the new ships replacement for the 3 inch guns?
And I always thought the view back in 5/38s back in 1938 as antiship much like the casemate 6 inchs of other battleships? or were they really thought of initially as both anti ship and anti air in 1934?
The only reason to go for a 3.5-inch gun over a 3-inch gun is the increase in slant range envelope. You're going to be looking at an additional 5,000 yards of range and 12,000 feet of altitude. The 90 mm gun actually has better ballistics than the 5"/38 but with significantly reduced shell weight. The problem is that the larger gun would have slower and heavier mounts, so they will be less effective at low altitude and against maneuvering targets and will be even more of a weight problem than the 3-inch twin RF mounts. In the US context in the post-war period where this is a serious possibility, the only targets the increase in AA envelope from 37k ft to 43k feet gets you are some high-altitude reconnaissance planes that aren't an immediate threat to the fleet and are better dealt with by planes. Pre-war, heavy AA (any non-automatic weapons) were not useful until air search radars with height finders could give the fuze setters accurate altitude data for targetting. There's no reason to eat the decrease in anti-ship performance in exchange for being able to shoot at a few Japanese snoopers
Dual purpose, the 38 length was half way between current 5”/25 for AA and 5”/51 antiship.
Yes the 12000 bhp diesel for centre shaft was to go on Prinz Regent Luitpold and another from a different manufacturer was to go in Sachsen. I think the coal crushing machinery was also weighty and the height of the diesel meant a hump had to be fitted to the armour deck was another disadvantage. Tirpitz was following the Turbo electric development also because Germany was the largest electric motor producer in the world so he wanted to support this industry. He wanted greater fuel efficiency for German ships.
They could, but Germany already used coal tar oil (refined from the tar that comes from carbonizing coal) for this purpose, both in their steam-powered battleships for oil spray (as in the SMS Von der Tann) and in their diesel engines (the battleship engine was delayed in WW1 because it had to be redesigned to use this fuel instead of normal diesel). It was about equal to oil in most performance aspects, and so they probably decided it was better than coal slurry.
2-stroke diesels are suitable to higher speeds (not as high as a turbine) but realistically high engine speeds aren't needed in a ship- the reduction gear/electric transmission whatever speed is required from the engine shaft. If anything gas and steam turbines require more reduction gearing to slow down the output speed to where a propeller is most efficient, and if a diesel engine can run slow enough to drive a propeller directly that's a big advantage (but even most diesel engines can't run that slow). So their speeds are suitable for any ship speed.
The main difference between diesels and turbines (steam or gas) boils down to: diesel engines generally weigh more, but consume less fuel.
This obviously depends on the engines being compared, and when turbocharged diesels were developed in WW2 they actually started to weigh less than steam turbines for the same power. Compared to coal-fired turbines, MAN in 1909 guaranteed its diesels would have 1/4 the fuel consumption by mass (0.2 kg/SHP). Compared to oil-fired turbines diesels may have had 1/2 the fuel consumption, and modern diesels might be around 30% more efficient than modern gas turbines. However, they usually were heavier.
Take the USS Oklahoma City, a WW2 Cleveland-class light cruiser. Her propulsion consisted of 4 25,000 HP shafts, each powered by a single M-type oil-fired boiler producing superheated steam, and a set of turbines. Each boiler weighed 175,660 lbs (79,678 kg)- about 80 tonnes. The turbine weight is not given, however the reduction gear (not included as it would probably be needed for diesels as well) weighed 62,000 lbs (28,123 kg), and the turbines appear similar in size and rotating mass, so about 25 tonnes seems reasonable for each set of them. There are other accessories like condensers but diesels also require systems like fuel filters and radiators, and I'll assume those weigh the same as the steam turbine accessories, cancelling out any weight difference. This produces a net total of 105 tonnes per 25,000 SHP- or 4.2 kg/HP.
Now, we can compare this to the various generations of marine diesels built by MAN for German warships. The first engine whose weight is mentioned is the Deutschland class' M9Z 42/58 from 1928, which weighed 100 tonnes and produced 7,100 HP- or 14 kg/HP. This is over 3 times worse than the Oklahoma City, but somewhat understandable since it was designed over a decade earlier. The next engine whose weight is mentioned is the L11Z 19/30 from 1933, with a weight of 3.8 tonnes and a power output of 1,400 HP continuous- or 2.7 kg/HP. This is better than the steam turbine, though it is a small torpedo boat engine, more comparable to the MB 500 series than large marine diesels. Next up is the M9Z 65/95 from 1938, with a weight of 225 tonnes and power output of 12,500 HP (almost the exact same as the original 1912 battleship engine)- or 18 kg/HP. This is not only worse than the steam turbine, but worse than the previous M9Z 42/58. It seems that the power-to-weight ratio decreases the bigger the diesel cylinders get.
After this V-engines were developed, starting in 1939 with the V12Z 42/58 with a weight of 136.5 tonnes and a power output of 15,600 HP- or 8.75 kg/HP. This is a major improvement over the previous large marine engines. In 1940 the V12Z 32/44 was developed with a weight of 50.8 tonnes and a power output of 10,000 HP- or 5 kg/HP. With the development of turbocharging, a turbocharged variant of the engine was developed with a weight of 60 tonnes and a power output of 16,000 HP- or 3.75 kg/HP. This engine finally had a higher power-to-weight ratio than the Oklahoma City's steam turbines.
Gas turbines arrived after WW2, but they have very high power-to-weight ratios- on the order of 100 times that of a diesel or steam plant.
In summary, the weight-to-HP ratio for very large engines is (lower is better):
~1940 turbines: 4.2 kg/HP
1928 M9Z 42/58: 14 kg/HP
1938 M9Z 65/95: 18 kg/HP
1939 V12Z 42/58: 8.75 kg/HP
1940 V12Z 32/44: 5 kg/HP
~1941 turbocharged V12Z 32/44: 3.75 kg/HP
I left out the L11Z 19/30 because it is too small to make a reliable comparison.
This may be compensated by the lower amount of fuel needed to obtain the same range- as that would decrease ship weight. However, if greater range with the same amount of fuel is desired, it will not affect much. There are also some other factors:
- From the oldmachinepress page: "Compared to a steam turbine, the diesel engine took up less space, was simpler to operate, had nearly instant power, and could suffer damage without disastrous consequences. Shrapnel passing through a diesel engine would shut down the engine, most likely one of several. Shrapnel passing through a steam boiler would cause the boiler to explode, most likely killing some of the crew in the room."
- From the Prinzregent Luitpold diesel page: "These opponents pointed out that the large diesels on the drawing boards of MAN were so tall that they would penetrate through the standard armored deck arrangement being designed into all Imperial German Navy battleships of the day. In addition, the wholesale elimination of coal bunkers in the future meant that the entire battleship underwater protection scheme would have to be completely re-thought. This faction claimed that this meant that *additional* armor -- both horizontal as well as below the water line -- might in fact have to be added to ships, thus obviating the proclaimed weight savings."
- From the MAN 1912 diesel engine forum: "During all the intervening decades the diesel engine was more fuel efficient, but generally burnt more expensive fuel. Diesels freed up more space for cargo and didn't have any stand-by losses (whereas boilers and turbines required standby manning even when in port). However by the 1970's, diesel engines were burning the cheapest dregs of the refinery, just as boilers had been doing for years, and longer strokes meant they were able to run at the low shaft speeds previously reached only by the reduction-geared turbines. Last ditch efforts were made to increase steam conditions, but with diesels now burning the same fuel, there was no cost advantage left for the steam turbine."
- Burning less fuel means that critically for an oil-short country, diesels required less fuel consumption/stockpiles in total for the country to operate the navy (this is the main reason why I would personally favor diesels wherever practical).
- Both types of engine can be fitted with either reduction gearing or electric transmission, so there's not much difference there.
- Like gas turbines, they have much lower fouling and maintenance requirements, and a generally better work environment.
- From one book: "The airflow was about three times as much as a steam plant. Some 75 percent of the heat of combustion went into the exhaust gas at 500 C and 200 ft/s- in a steam plant 20 percent went up the funnel and 60 percent into the sea. The gas turbine air flow had to be unobstructed as 1" water gauge back pressure would reduce the steam power from an Olympus by 100 shp." (p. 94) In short the diesel requires smaller air intakes than a steam turbine, and much less than a gas turbine of equal power. Most modern ships have very large superstructures and are space-constrained in part because the intake and exhaust ducts for their gas turbines require so much room. Dealing with thermal signature on more modern ships is also easier for diesels than for turbines of either type.
Only for 2-stroke opposed-piston diesels, and for those ships are close enough to "constant load" that it works. Three comments (but not the only ones) about the Leyland L60 state:
The Napier Deltic family was also an opposed-piston 2-stroke (it, the CV12, and the L60 were all ultimately derived from the Jumo 204 aircraft engine) and it worked fine in fast attack craft with reduction gear drive. Only ground vehicles with mechanical transmissions have variable enough speed and load to really cause problems for these kinds of engines (which is why the same engines get used in aircraft, naval, locomotive, and power generator applications, but road vehicle engines are usually purpose-designed).
They were used in some US Standard-type battleships, the Lexington class battlecruisers/carriers, and a lot of WW2 destroyer escorts. There were also lots of steam turbine-electric destroyer escorts built. This was mainly done to reduce the need for limited gear-cutting capacity that reduction gears required. Ever since steam turbine reduction gears became possible in 1912, gear-cutting capacity was a limiting factor. Even the Oliver Hazard Perry class frigates in the 1970's had a single screw to make them easier to mass-produce for this reason. But electric motor/wiring capacity was always available for ships. Modern ships have electric transmissions, but for power-related reasons.
Other than that, the benefits and drawbacks of electric transmissions are as McPherson states- with a weight penalty for earlier designs. I think the USN determined that electric transmission in the USS New Mexico (1918) was about 6 times heavier than an equivalent reduction gear. The electric transmission can allow some weight-saving design features to partly compensate for this, and any improvement in efficiency can translate into less fuel stowage required, also partly compensating. With later developments the electric transmission generally became lighter, and after about 1950 improving technology and motor controls made them just as light as reduction gears.
Last edited:
Roon, Germany Pocket Battleship laid down 1929
Displacement:
10,386 t light; 11,018 t standard; 12,490 t normal; 13,668 t full load
Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
(531.75 ft / 527.00 ft) x 70.00 ft x (30.00 / 31.82 ft)
(162.08 m / 160.63 m) x 21.34 m x (9.14 / 9.70 m)
Armament:
8 - 9.37" / 238 mm 45.0 cal guns - 414.84lbs / 188.17kg shells, 150 per gun
Breech loading guns in turret on barbette mounts, 1929 Model
2 x Triple mounts on centreline ends, evenly spread
1 x Twin mount on centreline, forward deck centre
1 raised mount
8 - 5.90" / 150 mm 30.0 cal guns - 94.65lbs / 42.93kg shells, 250 per gun
Dual purpose guns in deck mounts, 1929 Model
8 x Single mounts on sides, evenly spread
12 - 0.20" / 5.1 mm 45.0 cal guns - 0.00lbs / 0.00kg shells, 1,050 per gun
Machine guns in deck mounts, 1929 Model
6 x Twin mounts on sides, evenly spread
Weight of broadside 4,076 lbs / 1,849 kg
Main Torpedoes
2 - 21.0" / 533 mm, 21.00 ft / 6.40 m torpedoes - 1.398 t each, 2.796 t total
submerged bow & stern tubes
2nd Torpedoes
6 - 21.0" / 533 mm, 21.00 ft / 6.40 m torpedoes - 1.398 t each, 8.388 t total
submerged side tubes
Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 5.00" / 127 mm 342.55 ft / 104.41 m 10.04 ft / 3.06 m
Ends: 1.00" / 25 mm 184.43 ft / 56.21 m 10.04 ft / 3.06 m
Upper: 1.00" / 25 mm 342.55 ft / 104.41 m 8.00 ft / 2.44 m
- Torpedo Bulkhead - Strengthened structural bulkheads:
1.00" / 25 mm 342.55 ft / 104.41 m 21.19 ft / 6.46 m
Beam between torpedo bulkheads 30.00 ft / 9.14 m
- Hull void:
0.00" / 0 mm 0.00 ft / 0.00 m 0.00 ft / 0.00 m
- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 5.50" / 140 mm 3.00" / 76 mm 2.00" / 51 mm
- Armoured deck - multiple decks:
For and Aft decks: 1.80" / 46 mm
Forecastle: 1.00" / 25 mm Quarter deck: 1.00" / 25 mm
- Conning towers: Forward 2.00" / 51 mm, Aft 2.00" / 51 mm
Machinery:
Diesel Internal combustion motors,
Geared drive, 2 shafts, 77,648 shp / 57,925 Kw = 30.00 kts
Range 10,000nm at 15.00 kts
Bunker at max displacement = 2,650 tons
Complement:
589 - 767
Cost:
£4.127 million / $16.510 million
Distribution of weights at normal displacement:
Armament: 854 tons, 6.8 %
- Guns: 832 tons, 6.7 %
- Weapons: 22 tons, 0.2 %
Armour: 2,249 tons, 18.0 %
- Belts: 907 tons, 7.3 %
- Torpedo bulkhead: 269 tons, 2.2 %
- Armament: 331 tons, 2.7 %
- Armour Deck: 696 tons, 5.6 %
- Conning Towers: 46 tons, 0.4 %
Machinery: 2,385 tons, 19.1 %
Hull, fittings & equipment: 4,818 tons, 38.6 %
Fuel, ammunition & stores: 2,104 tons, 16.8 %
Miscellaneous weights: 80 tons, 0.6 %
- Hull below water: 16 tons
- Hull void weights: 16 tons
- Hull above water: 16 tons
- On freeboard deck: 16 tons
- Above deck: 16 tons
Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
16,987 lbs / 7,705 Kg = 41.3 x 9.4 " / 238 mm shells or 2.3 torpedoes
Stability (Unstable if below 1.00): 1.15
Metacentric height 3.8 ft / 1.2 m
Roll period: 15.1 seconds
Steadiness - As gun platform (Average = 50 %): 71 %
- Recoil effect (Restricted arc if above 1.00): 0.84
Seaboat quality (Average = 1.00): 1.48
Hull form characteristics:
Hull has a flush deck,
a normal bow and a cruiser stern
Block coefficient (normal/deep): 0.395 / 0.408
Length to Beam Ratio: 7.53 : 1
'Natural speed' for length: 22.96 kts
Power going to wave formation at top speed: 56 %
Trim (Max stability = 0, Max steadiness = 100): 48
Bow angle (Positive = bow angles forward): 4.00 degrees
Stern overhang: 3.00 ft / 0.91 m
Freeboard (% = length of deck as a percentage of waterline length):
Fore end, Aft end
- Forecastle: 20.00 %, 25.00 ft / 7.62 m, 25.00 ft / 7.62 m
- Forward deck: 30.00 %, 25.00 ft / 7.62 m, 25.00 ft / 7.62 m
- Aft deck: 35.00 %, 25.00 ft / 7.62 m, 25.00 ft / 7.62 m
- Quarter deck: 15.00 %, 25.00 ft / 7.62 m, 25.00 ft / 7.62 m
- Average freeboard: 25.00 ft / 7.62 m
Ship tends to be wet forward
Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 210.7 %
- Above water (accommodation/working, high = better): 183.0 %
Waterplane Area: 22,632 Square feet or 2,103 Square metres
Displacement factor (Displacement / loading): 121 %
Structure weight / hull surface area: 134 lbs/sq ft or 654 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.88
- Longitudinal: 3.42
- Overall: 1.00
Extremely poor machinery, storage, compartmentation space
Excellent accommodation and workspace room
Ship has slow, easy roll, a good, steady gun platform
Good seaboat, rides out heavy weather easily
A design that I believe, is superior in some respects to the Deutschalnd class by being cheaper.
Displacement:
10,386 t light; 11,018 t standard; 12,490 t normal; 13,668 t full load
Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
(531.75 ft / 527.00 ft) x 70.00 ft x (30.00 / 31.82 ft)
(162.08 m / 160.63 m) x 21.34 m x (9.14 / 9.70 m)
Armament:
8 - 9.37" / 238 mm 45.0 cal guns - 414.84lbs / 188.17kg shells, 150 per gun
Breech loading guns in turret on barbette mounts, 1929 Model
2 x Triple mounts on centreline ends, evenly spread
1 x Twin mount on centreline, forward deck centre
1 raised mount
8 - 5.90" / 150 mm 30.0 cal guns - 94.65lbs / 42.93kg shells, 250 per gun
Dual purpose guns in deck mounts, 1929 Model
8 x Single mounts on sides, evenly spread
12 - 0.20" / 5.1 mm 45.0 cal guns - 0.00lbs / 0.00kg shells, 1,050 per gun
Machine guns in deck mounts, 1929 Model
6 x Twin mounts on sides, evenly spread
Weight of broadside 4,076 lbs / 1,849 kg
Main Torpedoes
2 - 21.0" / 533 mm, 21.00 ft / 6.40 m torpedoes - 1.398 t each, 2.796 t total
submerged bow & stern tubes
2nd Torpedoes
6 - 21.0" / 533 mm, 21.00 ft / 6.40 m torpedoes - 1.398 t each, 8.388 t total
submerged side tubes
Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 5.00" / 127 mm 342.55 ft / 104.41 m 10.04 ft / 3.06 m
Ends: 1.00" / 25 mm 184.43 ft / 56.21 m 10.04 ft / 3.06 m
Upper: 1.00" / 25 mm 342.55 ft / 104.41 m 8.00 ft / 2.44 m
- Torpedo Bulkhead - Strengthened structural bulkheads:
1.00" / 25 mm 342.55 ft / 104.41 m 21.19 ft / 6.46 m
Beam between torpedo bulkheads 30.00 ft / 9.14 m
- Hull void:
0.00" / 0 mm 0.00 ft / 0.00 m 0.00 ft / 0.00 m
- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 5.50" / 140 mm 3.00" / 76 mm 2.00" / 51 mm
- Armoured deck - multiple decks:
For and Aft decks: 1.80" / 46 mm
Forecastle: 1.00" / 25 mm Quarter deck: 1.00" / 25 mm
- Conning towers: Forward 2.00" / 51 mm, Aft 2.00" / 51 mm
Machinery:
Diesel Internal combustion motors,
Geared drive, 2 shafts, 77,648 shp / 57,925 Kw = 30.00 kts
Range 10,000nm at 15.00 kts
Bunker at max displacement = 2,650 tons
Complement:
589 - 767
Cost:
£4.127 million / $16.510 million
Distribution of weights at normal displacement:
Armament: 854 tons, 6.8 %
- Guns: 832 tons, 6.7 %
- Weapons: 22 tons, 0.2 %
Armour: 2,249 tons, 18.0 %
- Belts: 907 tons, 7.3 %
- Torpedo bulkhead: 269 tons, 2.2 %
- Armament: 331 tons, 2.7 %
- Armour Deck: 696 tons, 5.6 %
- Conning Towers: 46 tons, 0.4 %
Machinery: 2,385 tons, 19.1 %
Hull, fittings & equipment: 4,818 tons, 38.6 %
Fuel, ammunition & stores: 2,104 tons, 16.8 %
Miscellaneous weights: 80 tons, 0.6 %
- Hull below water: 16 tons
- Hull void weights: 16 tons
- Hull above water: 16 tons
- On freeboard deck: 16 tons
- Above deck: 16 tons
Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
16,987 lbs / 7,705 Kg = 41.3 x 9.4 " / 238 mm shells or 2.3 torpedoes
Stability (Unstable if below 1.00): 1.15
Metacentric height 3.8 ft / 1.2 m
Roll period: 15.1 seconds
Steadiness - As gun platform (Average = 50 %): 71 %
- Recoil effect (Restricted arc if above 1.00): 0.84
Seaboat quality (Average = 1.00): 1.48
Hull form characteristics:
Hull has a flush deck,
a normal bow and a cruiser stern
Block coefficient (normal/deep): 0.395 / 0.408
Length to Beam Ratio: 7.53 : 1
'Natural speed' for length: 22.96 kts
Power going to wave formation at top speed: 56 %
Trim (Max stability = 0, Max steadiness = 100): 48
Bow angle (Positive = bow angles forward): 4.00 degrees
Stern overhang: 3.00 ft / 0.91 m
Freeboard (% = length of deck as a percentage of waterline length):
Fore end, Aft end
- Forecastle: 20.00 %, 25.00 ft / 7.62 m, 25.00 ft / 7.62 m
- Forward deck: 30.00 %, 25.00 ft / 7.62 m, 25.00 ft / 7.62 m
- Aft deck: 35.00 %, 25.00 ft / 7.62 m, 25.00 ft / 7.62 m
- Quarter deck: 15.00 %, 25.00 ft / 7.62 m, 25.00 ft / 7.62 m
- Average freeboard: 25.00 ft / 7.62 m
Ship tends to be wet forward
Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 210.7 %
- Above water (accommodation/working, high = better): 183.0 %
Waterplane Area: 22,632 Square feet or 2,103 Square metres
Displacement factor (Displacement / loading): 121 %
Structure weight / hull surface area: 134 lbs/sq ft or 654 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.88
- Longitudinal: 3.42
- Overall: 1.00
Extremely poor machinery, storage, compartmentation space
Excellent accommodation and workspace room
Ship has slow, easy roll, a good, steady gun platform
Good seaboat, rides out heavy weather easily
A design that I believe, is superior in some respects to the Deutschalnd class by being cheaper.
Thank you for all that! My notes indicate that there are two types of coal tar, lignite and regular coal derived, Germany possessing lignite in abundance, and that type being better in diesels, I presume the other better in boilers, gives me a push towards diesels in step with historic efforts. Behind my question is the assumption that Germany only has Romania as a (relatively) secure supply of petroleum potentially followed by Ottoman oil from Mesopotamia, and either a friendlier Russia, USA and/or DEI, but none really secure comparably to Persia for the RN. So an alternative is mandatory. I assume an equally dismal 1930s through 1940s, so stockpiling imported oil is good but expensive to foreign exchange and argues for an ersatz oil program using coal. By the 1930s the Army and Navy air forces will be demanding gasoline as will a mechanizing Army, so there goes oil stockpiles, again the Navy is needing its own supply. So I will rely upon coal tar oil as a back up strategic oil supply as Germany transitions from coal fired to oil fired propulsion, especially for lesser ships moving to diesel, attempting to stockpile petroleum and secondarily developing coal slurry technology parallel with the railroad. That saves me space and crew from stokers, gains some advancements towards oil firing, opens up RAS and improves German technology that can transfer into commercial application.
As an aside given the excessive weight and poor performance of the 5.25" mount the Royal Navy would probably have been better off with a mixed updated 5.5" LA and 4" HA armament.
http://www.navweaps.com/Weapons/WNBR_525-50_mk1.php
http://www.navweaps.com/Weapons/WNBR_55-50_mk1.php
http://www.navweaps.com/Weapons/WNJAP_55-50_3ns.php
http://www.navweaps.com/Weapons/WNBR_4-45_mk16.php
I doubt that a mixed battery would not cost more in weight and space?
The 5.25" in twin turrets with directors is probably already more effective as a surface wepon than the single 5.5" and you would need to add the weight of casements or splinter protection as well as the larger crew.... before you add the weight of the AA guns?
The school of thought for a separate anti-surface and anti-aircraft battery is more than out there in the interwar or WWII period, the only nations to formally adopt the dual purpose nature of secondary batteries is the United Kingdom and the United States, potentially to their detriment. The 5"/38 was a potent anti-aircraft weapon but a lackluster anti-surface weapon, the 5.25" was the opposite. Obviously every other nation did not particularly think the compromise of going dual purpose was worth it.
Because the two largest navy's with the best R&D departments are insignificant even if they built more battleships than the rest combined.... or that French also tried they just didn't make it work well http://www.navweaps.com/Weapons/WNFR_51-45_m1932.php.
With hindsight I think a 4.5" with split loading is very hard to argue with?
I never said they are insignificant, I'd rather you not try and speak for me. Out of the naval powers which built capital ships in the interwar period, only the United Kingdom and the United States stayed with dual purpose batteries. The French failed with the Dunkerque's and moved back to a split battery with Richelieu, the Italians stayed with a split battery with Littorio, the Germans had split batteries all along the way and the Japanese had the same with the Yamato's. They issues with creating a suitable dual purpose battery was either too much or wasn't seen as worth the effort, hence why the Germans in their various Plan Z ships attempted in the design stage but never actually had a platform materialize.
Best R&D departments are questionable given the absolute logistical mess that was Royal Navy ordnance during the interwar and WWII period, four vs two navies seems to speak for itself.
The 4.5" Mark 6 was of late enough war vintage that I don't particularly count it during this time period, as I wouldn't count the 5"/54 either.
Sorry but I was just questioning your use of
I think the main trend of the big navies was to DP guns its just that the smaller navy's could not keep up or develop them in time or budgets.
USN - DP 5"/38
RN - DP lots of tries......
IJN - DP 12.7 cm/40 (5") Type 89....Yamato class just was sufficiently large to add a 6" set as well.....
NM - DP early adopter 130mm but didn't work well on Dunkerque class so reverted later
RM - none DP
KM - none DP
With the navy's in rough size order (in 30s) I think its clear that DP was the way forward?
For IJN I would go with the 10cm/65 (3.9") myself..... I know it says AAA, but it is sweet for a light DP mount too.
http://navweaps.com/Weapons/WNJAP_39-65_t98.php
That would work well, though by the 1930's fully synthetic oil technology would supersede coal tar oil and slurry (or earlier depending on how fast the Bergius process was developed). Even for countries with naval superiority like the UK or Germany in some TLs, it's a good idea to develop substitutes for strategic materials (like oil), because if an opponent doesn't make the mistakes Germany did with their submarine campaign, then it's likely the merchant fleet supplying those materials will get sunk regardless of naval power. So for the WWI-era coal tar oil or coal slurry would be a decent substitute.
The IJN managed to create a twin 5.5" LA that weighed 49 tons, the RN's 4" HA Twin weighed 16 tons. The lightest version of the Mark I 5.25" DP was 77.5 tons, and had extra weight added once in service (With RP, the one on Vanguard, it went up to 95 tons). The Mark II was in the 84-96 ton range. Realistically you could install a twin 5.5" LA and two 4" HA twin mounts for each 5.25" mount, and still probably save weight.
Dual purpose mounts often seem to come across as a false economy when you take a careful look at them. Its one of those things that seems like a good idea, but may not actually be so. The RN's DP mount that actually worked the 4.5/45 Marks I-IV ranged between a twin mount of 37 to 49 tons. For a carrier, and this is a hindsight thing, an anti-surface capability is an optional luxury. For the same weight British carriers could have had 2 or 3 times the number of 4" mounts, if an Aircraft Carrier has to depend on its own integral armament to fend off a surface attack then something has gone horribly wrong and its not going to matter anyway.
It is not necessarily an advantage for lighter vessels either, Anthony Williams makes a convincing argument that RN Destroyers of WW2 would have been better off using an all 4" HA/LA armament as well http://www.quarryhs.co.uk/MCGWW2.html in that it would of produced a higher rate and volume of fire.
As the Royal Navy already had a 5.5" gun in service, and it knows that a practical twin mount can be built from the IJN's example, considerable time and money can be saved in not developing the 5.25" gun and mountings.
(And probably the proliferation of other designs as well)
Weight wise you need to add the full ship impact, such as crew, deck size & length, fire control directors, magazines and shell handling areas..... three mounts means far more of each of the above even a twin 5.5" and a twin 4" will cost more weight once you add them in, especially as the Twin 4" HA RN gun is hand worked open shield type with out the shell handing and hoists included in the 16t.....
Good points, but as jsb points out looking at pure tonnage is all well and good, but tonnage doesn't' necessarily mean space.
Deck space has to be taken into account.
In the early war I' put the 4.5s over the 5.25s in almost any take. Arguably with the fact they worked throughout the war better than the 5.25s gives them the advantage.
However by late war the bigger, larger caliber weapons having the improved fire control and the kinks removed became excellent weapons.
Still, look at Scylla. "The Toothless Terror"
You'd stuck your cheap bog standard 4" HA twin mounts and rigged it with a full fire control system made for a truly terrifying AA ship.