Japanese Coastal Defenses

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engineer
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Japanese Coastal Defenses

Post by engineer »

More than anyone ever wanted to know about Japanese Coast Artillery - a postwar monograph on the web via Carlisle here: http://www.carlisle.army.mil/cgi-bin/us ... docnum=726

A key note near the bottom of page 13 of the .pdf - some of the larger guns emplaced in the 1920s were from ships discontinued by the Washington Treaties, so they would be absent in any WPO scenario. This would put the Japanese plan back to the original strategy of 20 cm guns and 42 cm howitzers. The post WW1 upgrades wouldn't be complete for the early scenario, but probably would for the late scenario.
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RE: Japanese Coastal Defenses

Post by engineer »


The link above goes to a War Department white paper compiled early after the conclusion of the Second World War.  US personnel traveled all over Japan and interviewed surviving personnel, as well as physically inventoried much of the hardware.  The monograph covers the order of battle for Japanese coastal defenses in Japan and Korea, equipment, training, doctrine, and some history.  In short, this is a primary source document for this topic for both WPO and WITP. 
 
The WPO order of battle does not reflect the information in the document.  The variation between WPO and the white paper is both at a device and an LCU level.  Overall, I would say that WPO under-defends the Home Islands and over-defends her overseas possessions.  
 
The general shape of Japanese coast defenses war outlined prior to WW1. These defenses were under control of the Imperial Japanese Army. A thorough enhancement of the defenses took place in the early 1920s.  In the historical timeline, the Washington Treaties precluded the completion of many capital warships and those weapons were mounted in regular, naval-style turrets in several locations around the Home Islands and Korea.  The original plan, which would have taken place in the WPO timeline, called for the installation of dual 200 mm guns in naval-style turrets.  Also, many of the pedestal mounted 150 mm guns were updated to a 1936 model gun where a conventional wheeled field gun could be installed into a ring mount, tied into central fire control systems, and used for coastal defense prior to WW2.  Following the 1920s, there were little or no expansions to the defenses, given the offensive doctrine of the Japanese Empire. During the last year of WW2 a parallel system of naval coastal artillery was developed as the IJN found itself with fewer and fewer seaworthy ships yet still endeavored to contribute to the defense of the empire. 
 
With respect to WPO, the import of this data is pretty clear.  The naval coastal artillery can be disregarded (it’s all 1944 or later construction).  The heavy naval turret guns up to 41 cm would be replaced with 20 cm turrets.  The army coastal artillery except for late construction as noted in the text can be taken as present for the late WPO scenario.  The mobile 1936 model 15 cm guns would still be pedestal mounted 1912 model 15 cm gun (at a device level the ballistics would be identical, but the 1912 would have a much higher load cost). For the early scenario, it’s likely that all of the 20 cm turret guns wouldn’t be installed at the outset of the scenario, but completion by 1923 or 1924 would have been likely.  For simplicity’s sake, it’s a designer’s choice to use the same coastal OOB in both scenarios or add more fortification units in the reinforcement queue that would come on-board during the first 24 months of the early scenario as the 20 cm turret emplacements were completed.  I would recommend the same OOB.
 
The place where Japanese combat power takes a hit, is that there simply isn’t a 24 cm gun in their coastal artillery inventory.  The turret mounted 20 cm gun is the largest gun to be found.  It was in a twin turret with about 100 mm of armor.  The maximum range is 26,000 yards and the ammunition appears similar to 8 in shells in the US and UK arsenals.  The most numerous gun is a 15 cm gun.  Both the 15 cm and 20 cm guns were linked to central fire control operations in the various fortresses.  The Japanese also had a 10 cm gun that was widely used, but the 10 cm gun had strictly local fire control so accuracy at long range would be suspect.  There were also 7.5 cm and some 12 cm guns. 
 
The Japanese also used a lot of large caliber howitzers for coast defense.  These were weapons of 24 cm, 28 cm, and 30 cm size.  However, the ranges of the howitzers were quite short (9,000 to 17,000 yards).  Given the plunging fire associated with the howitzers, they would be similar to western CD mortars with large effectiveness and large penetration but poor accuracy.  Ellis’s World War II, A Statistical Summary[/i], confirms that the 24 cm weapon in the Japanese inventory only had a 9900 yard maximum range.  The 24 cm howitzer in the white paper is rated at 12,800 yards maximum range.  The ranges are close enough that the sources are probably referring to the same weapon. 
 
All of the weapons except the 20 cm rifles were provided with predominantly AP ammunition, and some HE was available for use against soft targets, such as enemy landing parties.  The 20 cm turret guns appear to have been pure AP in their load-outs. 
 
One other device point, the actual history of Japanese coast defense guns only shows one place where there was a tangible upgrade: from the fixed mount 1912 15 cm gun to the improved mount for the 1936 15 cm gun which allowed a wheeled gun to be used.  The WPO devices have an upgrade path that leads to bigger guns over time.  In the area of coastal artillery, there just isn’t good evidence to show that this would in fact occur so the device upgrade path should be closed off to keep the guns locked at the initial state (at least within the 1922-1930 window).
 
So from a device perspective, we see that the big gun in the Japanese arsenal is a 20 cm rifle.  Lots of 15 cm rifles are available at various locations.  The 10 cm rifle is also available, but has sub-par accuracy due to poor fire control.  Defenses on the Home Islands and Korea are supplemented with 24 cm, 28 cm, and 30 cm howitzers.  Moving the units overseas is unlikely since the turret device deserves a 9999 load weight (excavated magazine, shell hoists, crew quarters, etc.) and the small pedestal guns should still have a load weight of several hundred minimum since they would need to be emplaced in a reinforced concrete base.   (Tokyo has some artillery battalions that are pure howitzer and are therefore, readily sea-liftable).   For the 7.5 and 12 cm guns, I’m using the stock devices #275 and #294 respectively.
 
Recommended Draft Devices to follow (screenshots from the device editor)
 
I’ve been working on the OOB updates to incorporate this.  I’m about 70% done and will add that information when I get things completed.  The general shape of the OOB modifications is that Japan itself will have defenses on more hexes and the straits between Japan and Korea will be much more heavily defended.  For example, in stock WPO, the entrance to the Inland Sea via Matsuyama is undefended.  Historically, there were several units of coastal artillery responsible for defending this straight.  Likewise, Sasebo, Kagoshima, and Sendai had coast artillery, too.  In the Mandates and Formosa, the net effect will be lower quantities of coast defense artillery firepower by substituting 15 cm guns for the 24 cm guns.  
engineer
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20cm CD Gun

Post by engineer »

20cm, 47 caliber, Turret Mounted Coast Defence Gun


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engineer
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RE: 15cm CD Gun

Post by engineer »

15cm Type 45 Coast Defense Gun.

These typically had a gun shield for the crew, hence the armor for the gun.  Under the Japanese calendar, 1912 was their '45 so I've named the gun in accordance with the Japanese calendar.


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Oops, the armor on this one should be 25 to give credit for the gun shields in evidence for the photo's of the this model of CD gun.
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engineer
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RE: 10cm CD Gun

Post by engineer »

Here is the next CD gun.


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engineer
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24 cm CD Howitzer

Post by engineer »

Here is this weapon.



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28cm CD Howitzer

Post by engineer »

Here is this howitzer.


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engineer
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30 cm CD Howtizer

Post by engineer »

Here is this weapon.


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Rysyonok
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RE: 30 cm CD Howtizer

Post by Rysyonok »

Oh, you're making your own scenario? ^_^
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engineer
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RE: 30 cm CD Howtizer

Post by engineer »

Indeed, "Western Citadel" sweeps up all the miscellaneous changes, but also presumes that the US heavily fortified Guam in line with the Navy Department memoranda from December, 1919.  From there, a sister scenario that leaves a "weak" Guam in place is also logical.  However, without the Washington Treaties in place, this "weak" Guam would still be stronger than the historical Guam that the USA was prohibited from fortifying.
 
In my first test, the Japanese broke their teeth on Guam, but captured Wake.  Ten months into the war, Wake is the world's largest self-administered POW camp with over a 100,000 Japanese defenders.  US subs and cruisers are raiding the supply lines to Wake from bases at Midway, Eniwetok, and Guam.  Truk and Kwajelein are bypassed Imperial citadels. Japanese capital ships have savaged several of the raiding forces, but hundreds of 'Maru's have been sunk. The 1st Infantry and 1st Cavalry were broken in an unsuccessful invasion of Kwajelein that resembled nothing better than the opening Battle of Klendathu in Starship Troopers. US forces are about ready to launch from Guam to wrap up the Mariana's and the western Carolines. The Japanese bogged down in northern Luzon and the USA never lost Manila. (I'm going to have to repeat that several times to understand if it was a fluke or if I've broken something in the Japanese). The Asiatic Fleet was sunk in battle, but they must have disrupted the invasion task forces for Lingayen or Bataan.  The ZR3, USS Los Angeles, also successfully bombed the Ise while on naval search from Manila after transferring out from the West Coast.       
 
This alpha test has the Guam OOB changes and dirigibles.  As I get more experience with the system, I'm working on the research for next upgrade.  That will include the Japanese coastal defenses, updated allied transport OOB, tweaking the island characteristics in the Mandates, something different on the Atlantic Fleet (the most plausible scenario that I can imagine is that they are trapped on the lake in the Panama Canal when Japanese agents blow both ends of the canal so they arrive late but together after repairs to the canal), more wartime US construction (drydocks, submarines, destroyers, more late scenario battleships, airships, etc) in line with my estimates from the "Fortune Favors the Big Factories" thread.   
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Helpless
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RE: 30 cm CD Howtizer

Post by Helpless »

Did you test it against Japanese AI?
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RE: 30 cm CD Howtizer

Post by engineer »

Yes, and that's a place where I need to run multiple tests against different difficulty levels at least for the first few turns. 
 
 
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RE: 30 cm CD Howtizer

Post by Helpless »

I found that AI is very passive in WPO. Actually, I _never_ lost PI to Jap AI on hardest setting.
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RE: 30 cm CD Howtizer

Post by BigJ62 »

I've noticed that it also is very indecisive, splitting units apart after landing and in some cases not even waiting to unload then sending the units somewhere else, in the case of the P.I. invasion. I wonder if this is because the two grand campaigns have no production and use AI turned on? In WITP I was able to get the ai to behave more aggressively by making a few strategic changes, of course that's with production on and ai off, -not sure if makes any difference or not but just a thought-. However Tankerace hinted at the possibility of production in his latest post, so maybe there is hope yet. Engineer will you be able to add production into your scenario should it come to pass? Btw looks very promising I should like to try it out when your finished.

Thanks
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RE: Japanese AI & Production

Post by engineer »

I don't have any plans to tinker with production at this point.   
 
Reviewing my notes, I do see that the French cruiser force from Saigon intercepted a convoy off Luzon early in the test game.  Given the background of the scenario where the Europeans are really just friendly neutrals towards the US instead of active belligerents, I'm thinking that this bit should be changed to keep their squadron close to Saigon with a reaction mission instead of looking for trouble off Luzon. 
el cid again
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RE: Japanese Coastal Defenses

Post by el cid again »

There are substantial errors here. The standard Japanese turrets were identical - and had 12 inches of face armor - regardless of the caliber of gun mounted. There were a variety of these - from 8 to 16 inch - including a number of 12 inch in two variations. Speculation there might be 14 inch in US intel documents was incorrect. These guns do not date from 1944, but about 1934 - they were built after Fort Drum - but well before WWII. See Naval Weapons of World War II for details, including a listing of every battery.
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RE: Japanese Coastal Defenses

Post by String »

You might want to increase their accuracy considering that those weapons are only used in emplaced turrets.
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RE: Japanese Coastal Defenses

Post by engineer »

The historical CD batteries in WW2 used weapons that were surplused from capital ships scrapped or converted to CV's by the Washington treaty.  So in WPO the only turreted weapon that would be left is the 200 mm gun since the warships would be completed as planned.  According to the Carlisle monograph (and supplemented with lots of photos of the hardware), the smaller guns were in reinforced concrete pintle mounts.   The photo's of the howitzers show that they are wheeled or tracked.  Gun pits had been prepared so the crews would be protected from splinters and blast.  I'll double check the armor ratings on the turrets. 
 
On the 1944 naval/army issue, I was unclear.  Historically, the coast artillery was under Army control but the Washington Treaty resulted in a flood of navy ordnance getting incorporated in their inventory.  When the USA went in after WW2 to inventory the coast defenses they found two parallel systems.  The original Army system that had been built up over a period of decades and a new Navy controlled network of coastal defenses that had been assembled during the last years of WW2 as the IJN lost the ability to put ships to sea but recognized an ability to contribute to the defense of Japan by remounting ordnance in coastal batteries manned by sailors.  This latter system of coast defense would be beyond the scope of any WPO scenario since it wasn't created until years after the end of a WPO scenario.  It might be possible to simulate this by adding IJN coast defense artillery units reinforcements to the order of battle, but that would involve making some a priori assumptions that the IJN would be getting badly defeated at sea, as they were in WW2.  I haven't elected to do that. 
     
I'll double check the accuracy, but I'm pretty sure that I lined it up with other CD guns, all of which would benefit from typically being pre-registered from pre-war gunnery drills.  Howitzers, being indirect fire weapons, have a lower accuracy than direct fire weapons across the board. 
 
I don't have the Weapons of WW2 reference on my bookshelf, but the Carlisle document is a primary source compiled by individuals who made first hand inspection of the topic.    Interpreting that into game terms is a different question, and I bear full blame if I misconstrue the data.   
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RE: Japanese Coastal Defenses

Post by engineer »

El Cid Again, good catch on the turret armor. I verified 12 inches on the front and sides, 4 inches on the turret roof.  In addition, the turrets were semi-recessed in the earth so only a portion of the turrets were above grade. 
 
String, I double checked the accuracy values and the Japanese CD guns ended up typically at or near the top of the accuracy values for similarly sized Allied CD guns.  Older models of CD artillery are typically lower.  The Japanese 100 mm CD gun is an exception to that rule since the US survey commented that that specific gun had poor quality range-finding equipment. 
 
The recessing the guns below grade raises an interesting point.  It was customary at the time to dig in the indirect fire weapons  so they were below grade and relatively immune to flat trajectory gunfire.  A good example of this can be seen on Corregidor with the 12" mortar batteries there.  It's also the idea behind the disappearing mounts such as can be seen at the forts preserved at the mouth of Mobile Bay, on the Washington side of the mouth of the Columbia River or Fort Derussey on Oahu.  The idea would be to take a second look at the CD artillery and give the indirect fire weapons something like a 400 mm armor rating to account for the earthwork and reinforced concrete emplacements that typically sheltered these weapons. 
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