1930's Japanese Navy - What would you have done differently?

One thing I noticed about Japanese cruisers compared to their US counterparts - a big difference in main turret armor. The US cruisers seem to have about 6-8 inches in frontal turret armor, a couple inches on the sides and rear, 2-3 inches on turret tops and 5-6 inches in the Barbettes.

Japanese cruisers on the other hand seem to have about 1 inch of turret armor, and roughly 3-5 inches on the barbettes.

I wonder why? Was the lack of turret armor an attempt to make the vessels not as top heavy so they could carry torpedoes?

I suspect that it was because the IJN concluded that they would be unable to adequately armor their cruisers against gunfire at reasonable range, so they just put enough armor on their turrets to keep out splinters and machine gun fire.

The barbettes may have as much armor as they do because it was needed for strength.

I was thinking about it, the barbettes protect the magazines horizontally, the decks protect them vertically. The turrets may have egress to the magazines, but destruction of a turret is not an automatic by any means magazine fire. A penetrating strike to the barbette usually means an issue with the magazine.

My big surprise though is that a Common 5" shell from a US 5"/38 can penetrate an inch of armor up to a about 10 kilometers or so. The Japanese destroyers most common main armament of a 5"/50 penetrates a bit better than the US 5"/38 with a common shell. I'd think that one would want as a heavy cruiser to be able to proof one's main turrets from destroyer fire at least.

But my question really is where the turrets left "poorly armored" to make allowances for the weight of the torpedoes and tubes?

Garyt said:

But my question really is where the turrets left "poorly armored" to make allowances for the weight of the torpedoes and tubes?

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I don't know for sure, but that was probably one reason. I remember reading that Japanese ships also tended to be structurally inefficient, so their hulls were heavy for the ships' displacements, so that may have been another factor. Within the confines of a fixed displacement, adding weight to armament means that it's got to be removed someplace else.

Well, if indeed the turrets were lightened due to carrying torpedoes on deck, that is another drawback of the heavy cruiser being torpedo armed.

The Japanese could NOT design cruisers that would fight the US cruisers one on one (or eight on eight) as by the 1930 London naval treaty the Japanese were limited.

"The number of heavy cruisers was limited - Britain was permitted 15 with a total tonnage of 180,000, the US 18 totalling 147,000 and the Japanese 12 totalling 108,000 tons. For the light cruisers no numbers were specified but tonnage limits were 143,500 tons for the US, 192,200 tons for the British and 100,450 tons for the Japanese."

Granted the US might not be able to put all it's cruisers in the Pacific at once but in a big fleet action (or even a series of actions) the Japanese cruisers would be out numbered by the American cruisers. They had to have something to equalize the numbers. Assuming 1-2 Cruisers in dock for refit-repair and 1-2 on other duties (and similar proportion for the US and you might see 8-10 Japanese Cruisers trying to fight 12-15 American cruisers.
DO they go with the torpedoes or hope the Americans leave 40% of their fleet in Atlantic and try for a dead even fight with no hope of replacement ships while the Americans have that 40% reserve?

A typical IJN CA was the Chōkai..... a Takao-class heavy cruiser, armed with ten 20 cm (8 in) guns, four 12 cm (5 in) guns, eight tubes for the Type 93 torpedo, and assorted anti-aircraft guns. Range 8000 miles at 14 knots and a normal complement of 873

Northampton was a contemporary in the USN . She was armed with 9 × 8 in (200 mm)/55 cal , 8 × 5 in (130 mm)/25 cal Mk 10 guns (4x1) , 9 × 21 in (530 mm) torpedo tubes (3x3 which were removed), 24 × 40 mm Bofors AA cannons (6x4), 28 × 20 mmOerlikon AA cannons (28x1). Displacement was 9800 tons. Complement was 1100 men. Endurance unknown but a lot less than the Chokai.

In terms of armour distribution, the Japanese cruiser was lighter in the superstructure area , but much heavier in terms of deck armour and hull protection. US cruisers were built on the "all or nothing" principal, which meant there were many areas on US cruisers that had no protection, whilst Japanese protection schemes tended to have armour more evenly distributed . Overall, the Chokai had about 40% more armour worked into the ship compared to the Northampton.

Picking one area can yield inaccurate results. US might have better protection in some areas, whilst the IJN might be better protected elsewhere. At 15000 tons to 9000 the Japanese ship is bound to have better overall protection.

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northamptons armouring scheme was a max of 3in over the machinery, 1in deck, 3.75in side armour and 2in deck armour over the magazines. The main gunhouses had 2.5in face armour, 2in roof and 0.75in side and rear.

Chokai had a main belt of 3.9 in, 4.9 in side and deck armour around the magazines, 1 to 4 in armour worked into the deck. The turrets were weakly protected, with only 1 inch face protection and splinter protection only on the sides or rear. The reason should however be fairly obvious. The northampton had three turrets, with the guns grouped in threes. For Chokai there were five turrets, with each turret holding two guns. A knocked out turret for Chokai represented a 20% loss of gun firepower for the ship, whereas the Northamptons turrets each represented 34% of the ships firepower.

AS built the Northampton's had only 4 × 5 in (130 mm)/25 cal Mk 10 guns (4x1) , 6× 21 in (530 mm) torpedo tubes (2x3 which were removed) (Wiki being in error and the Light AA added to the survivors as the war went on.

The next class, Portland, as built lost the tubes and went to 8 × 5 in (130 mm)/25 cal Mk 10 guns (8x1 ) and 8 X 0.5in MG.

These classes were being built so fast, in the sense of being ordered and laid down, not in the sense that they were actually being constructed fast, it taking 2-3 years from laying down to commissioning, that lessons learned while building the early ones were not able to be fully applied to the next class.

AS built the Chōkai/ Takao-class heavy cruisers had 4 four 12 cm (4.7 in) guns, eight tubes for the Type 93 torpedo (4 X 2), and a few assorted light anti-aircraft guns (two 2pdrs?).

The Japanese rebuilt the Takao-class to a greater or lessor extent depending on which ship before the war (in the Pacific, work was being done on some ships in 1940) and AA armament changed to 8 12.7cm (5in) guns in all with variations in light AA and torpedo tubes between ships.

Mid to late 30s would have been an awkward time to try to rebuild ships to a new tactical philosophy. While you can futz around changing AA guns (even 12-12.7cm guns) doing substantial changes to turrets, barbettes, deck armor and the like is a LOT more work. Yes the Japanese did it to the Mogami's but without the treaties they might have been more inclined just to build new cruisers.

The Nachi class started laying down in 1924, the Takao's in 1927 and the Mogami's in 1931.

The US laid down the Pensacola in 1926, the Northamptons in 1928, the Portlands in 1930 and the New Orleans class started in 1930.

Obviously nobody had any fighting experience with such ships ( director control for battleships being only about 13-15 years old when they were laid down) and carrier aircraft were fabric covered bi-planes with fixed pitch props and 600hp engines IF they were very lucky. And for the US the Lexington and Saratoga didn't even commission until the end of 1927. Too late for any war game lessons ( except table top or meeting hall floor games) to be applied to the first 2 classes of cruisers even if the results of such war games had been allowed to show anything.

Mid to late 30s would have been an awkward time to try to rebuild ships to a new tactical philosophy. While you can futz around changing AA guns (even 12-12.7cm guns) doing substantial changes to turrets, barbettes, deck armor and the like is a LOT more work.

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Really, the only changes I would think needed on the Cruisers would be better AA. The 3.9"/60 would have been first choice, but I'm not sure of the availability of these guns, both when and how many were available. A better weapon then the 25mm probably would not be a bad idea, but I think there were other factors that made the 25mm less effective, most notably being the fire control on the weapon.

How about Japanese destroyers? Personally, I think they may have been the best destroyers of the war. Certainly better in a surface action than almost anyone else. Combination of usually 6 5" guns and the Long Lance made them deadly.

The only real issue i have is the dual mount for the 5"/50 did not traverse quick enough, and without a power rammer it was slow to load when elevated. Some mounts did not even elevate over 40 degrees, makes them almost useless in an AA role. Fix these issues with the 5" armament and I think they are in great shape.

Note- The us 5"/38 reported a great ROF, though there are a few issues here. The 5"/38's ROF depended upon the mount, some destroyers had the faster loading mounts, others were limited to a more pedestrian 12-15 rounds per minute.

Secondly, a high ROF in surface action is rather misleading. Here are the ranges and the time the round takes to get to target:

5,000 yards (4,570 m): 8.0 seconds
10,000 yards (9,140 m): 22.0 seconds
15,000 yards (13,720 m): 43.0 seconds
17,270 yards (15,790 m): 68.8 seconds

Even at 5,000 yards, you need 8 seconds to see where your round hits, then you need time to correct. So any rate of fire in excess of about 6 per minute is somewhat useless at 5,000 yards. You either have to me at point blank range or you are just firing without bothering to correct aim (most likely at point blank range)for a high rate of fire to really help.

And at 10 rounds per minute, the 5"/50 certainly had the required ROF for most surface actions.

Of course, this also speaks of the single mindedness of much of the Japanese Navy - destroy the opponents surface fleet with your surface fleet.

One destroyer class the Japanese built later in the war was the Matsu class. Smaller than most Japanese destroyers, only 3 main guns (and not the 5"/50), not a lot of torpedo tubes, slow (27 knot max). But these were very inexpensive vessels, and could hunt subs as well as a full blown Japanese destroyer. Japan would have fared better if more of these vessels were built early in the war.

The better gun for the Japanese was the 3.9. Had a sustained rof of 15-21 rpm a horizontal range of 19000m, and n effective ceiling of 13000m. The twin mounting weighed 34 tons
The 5/50 1914 pattern in the standard mount weighed 30 tons for a single gun mount. the sustained rof was 8rpm. Horizontal range was 18400 m and verical range on the 70 deg mount was about 10000m, The newer 5/50 type 1 (1941) had a maximum 22500m and a ceiling of 16200m. A new turret was designed for this gun, with a traverse speed of 18deg per sec, and a sustained rof of 13-18 rpm. There was never a turretted version design, but the land based mount that was built was 19000kg

If it had been possible to re-equip with the 3.9, which entered production in 1938, the IJN DDs would have gone into battle with roughly twice the numbers of guns in their DDs able to fire further, faster, more accurately and deliver a heavier broadside. It would have been about the same as the 5/38 mount (per gun) in AA, and somewhat more efficient in surface capability.

Japan never had the slightest chance of re-equipping with the 3.9 however.

The sustained OF for the 5"/50 was 10 rpm, and the twin mount weighed 32 tons.

I do believe the 3.9"/60 was a good weapon, the best for AA the Japanese had. I have concerns about it's use as a surface to surface weapon though. A few problems:

1) The Japanese never developed a common round for this weapon, only HE, and my concern here is if they did not develop a round for surface to surface action, did they perhaps not have faith in the weapon for that type of use?
2) The rate of fire as I have mentioned above is very misleading when it comes to surface to surface combat. It's similar to Battleship rates of fire, when one gun has a rate of fire of say 1.5 and another of 2.5. At 30,000 yards, you are looking at a good 50 seconds between when a round is fired and when you see the splashes. Then a bit to adjust the gun usually, so at this range one per minute is just fine. For a 5" type gun, a rate of fire of 10 is more than sufficient unless you are at close to point blank range, maybe 3000 yards or less, where you are looking at maybe 3.5 seconds from firing to splash or hit. So a 3.9"/60 may have a theoretical better broadside when it comes to projectile weight x rate of fire, but in practice the 5"/50 may come out ahead due to heavier shell weight and the 3.9"/60's ROF being supressed due to practicality.
3) The 5"/50 has far better penetration characteristics, as well as a more damaging charge. At about 5,000 yards, the 3.9" penetrates a bit better than an inch, whereas the 5" is looking around 3.5". Even with a HE round, the 5"/50 penetrates a bit better than 2".

Not that the 3.9" is useless for surface to surface by any means - I just think you are better off with the 5"/50 in this situation.

The 3.9" however is a far better AA weapon, so pick your poison I guess.

I just think the 5"/50 was a fine weapon in some regards, with a few modifications like faster turret, a power rammer and the ability to elevate to 75 degrees or better gives you a better dual purpose weapon. Plus as you mention the 3.9" was difficult to come up with in the numbers Japan would need to retool.

What might have worked the best was to have 3 types of destroyers, a "fleet" destroyer like the Akitsuki class, a surface action destroyer like the Asashio class, and a anti sub version like the Matsu class. Prett much what the Japanese did other than there were never enough Akitsuki's to go around, and they should have started earlier and produced more of the Matsu's.

Only difference is I'd like to see the 5"/50 re-designed a bit per my above comments.

ive seen data that says the 3.9 was issued with SAP and AP rounds, but ill check further tonite

well, accordig to campbell, 10cm/65 came in brass casing fixed ammunition, firing nose fuzed HE ammunition and a special ASw round (i confess i dont know what that is).

I checked the 5/50 type 1914....the standard DD gun for IJN destroyers. According to Campbell "Nose fuzed HE of two different types was carried and there were also two types incendiary shrapnel and two types illuminating shrapnel and the ASW round again.

So greater choice ion the 5in calibre, but neither was intended as an AP or SAP round.

I checked the 5/50 type 1914....the standard DD gun for IJN destroyers. According to Campbell "Nose fuzed HE of two different types was carried and there were also two types incendiary shrapnel and two types illuminating shrapnel and the ASW round again.

So greater choice ion the 5in calibre, but neither was intended as an AP or SAP round.

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Naval shells use different specifications and designations instead of AP/SAP/HE.

They indeed have AP and HE designations, but not SAP. And probably the closest thing to SAP is what they call a "common" round, which is in essence a HE round but with thicker walls designed to penetrate lighter armor.

As a real rough rule of thumb, "Common" rounds are designed to penetrate 1/3 their diameter, so in the case of a 5" shell it should penetrate 1.67". There are so many variables here, so it indeed is a real rough estimate. Muzzle velocity of the gun, range, butt or base fuse, angle, hitting near a joint are just a few of the many variables. But this penetration should penetrate most destroyer armor. It is said that destroyers have no armor, but this is incorrect, it's usually around 1" or 25mm or so of thickness, so a 5"Common round will generally have enough to penetrate a destroyers armor.

These different designation's are compounded by the US use of a "Special Common" round, which is a little but thicker walls and a smaller bursting charge. This round gives the US 5"/38 gun similar performance to the Japanese 5"/50 when it comes to penetrating armor - at the expense of a smaller bursting charge.

It gets a bit confusing when it comes down to caps and wind screens, I know the US common rounds did not have either, not 100% sure of other navies. And I thought, but I could be wrong that common rounds were butt fused. Perhaps it is the Special common round that is butt fused.

But the point of all this is that AA rounds were high explosive, and the preferred round for surface to surface combat was the Common round or Special Common. AA or HE rounds had a larger bursting charge than common rounds, though thinner shell walls and correspondingly less penetration.

And my point behind all this is that the 3.9" had a HE/AA round, but not a common round designed for it, while the 5"/50 did have common rounds.

Some publications do not differentiate between Common and standard HE. So you don't think I made these up , here is a good guide for shell designations:

Definitions and Information about Naval Guns - Part 2

and a special ASw round (i confess i dont know what that is).

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A blunt "diving shell" type of round, used obviously against subs, but I'm not sure of it's sucess. The Japanese had researched "diving shells", as far as I know other no other navy did anywhere this degree of research. They had some designed for surface to surface as well, and this is one reason why later Japanese battleships had a much more substantial lower belt than other countries battleships.

Shells generally have a tendency to "skip" if they have a relatively flat trajectory, the diving shells were modified not to skip but to dive. My guess is the ASW shells are similar.

Destroyers rarely had armor. Local Splinter protection yes but even engine spaces were rarely protected by more than hull plating.
Japanese might have been better served using their 5"/40 guns on their destroyers rather than the 5"/50s. Loss of longer ranges is pretty much an illusion as destroyers were usually pitching and rolling too much to do good work at max ranges. That is assuming they could even spot their shots at much over 12-14000 meters. The 5"/40 at least had all elevation loading.

Destroyers rarely had armor.

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It depends what you define as armor. Splinter protection is usually a good inch thick. If a hull is 3/4 to an inch thick is that armor? Well, it still must be penetrated if one want the explosive effects of a round to not merely explode on the outside of the steel. And steel does not have to be face hardened to serve as armor. The Fletcher class has 1/2 to 3/4 of an inch of steel over almost all of the vessel. Some areas were reinforced a bit thicker.

While 1/2 to an inch of non face-hardened steel is not much when you are looking at cruiser guns or bigger, it can pose an obstacle to 5" rounds or smaller that are not armor piercing. And the Naval versions of 5"or smaller rounds were almost never armor piercing.

One the other hand, when a 8" or bigger AP round hits 1" or less of steel, it well generally penetrate through the vessel before the fuse is set off.

You might be right though on the idea of the 5"/40. It's got a bit less range than the US 5"/38, and significantly less range than the 5"/50. The range does effect more than extreme range though, it effects all ranges other than point blank. As the descent angle of a shell increases, it's accuracy decreases. Of course the more extreme the range the more this effects a round, but it has an effect even at shorter ranges.

Though is this and greater penetration enough to make up for the shortcomings of the 5"/50 as an AA weapon? Perhaps not. The 5"/40 twin mount is about 4 tons lighter than the 5"50, so that is another thing to factor in.

One thing is for certain though, the Japanese were very much in love with the 5"/50. I would think because of it's excellent performance in the surface to surface role. And with the usual complement of 6 of these, they certainly outgunned about all US destroyers who were looking at usually 4-5 5"/38's.

They carried a few more guns, and had guns that performed better in the surface to surface role. Sounds like this was part of that Japanese strategy of outgunning their US opponents on a 1-1 basis, which indeed they did. And again, this showed Japan's lack of focus on vessels that were more multi-purpose.

A quick reason why I think the 3.9" was made only in an HE version, and the 5"/50 with the common round - I'd think the Japanese would want to do what they could to maximize the bursting charge of the smaller 3.9" shell to make it more effective in an AA role. The 5"/50 common round was probably deemed to have a sufficient charge for AA, OR the Japanese did not look at this weapon as a truly dual purpose weapon. Either could be correct.

And another reason why the Japanese likely really loved the 5"/50 - It could be a threat to a cruiser, where a lower velocity and/or hi explosive round would not be. Not to say the 5"/50 could with certainty penetrate a cruisers armor, as there are too many factors such as range, angle, and most importantly armor carried by the cruiser and exactly where the shell hits. I won't go into detail with various cruisers, armor carried and penetration ability of various weapons at range, but suffice to say it (the 5"/50) at least constitutes a threat to many cruisers.

Dupe entry

Hull plating is NOT armor. Armor does NOT have to be face-hardened. Destroyer hull plating was often not the same As cruiser, battleship, or merchant hull plating.
Some countries used high-tensile steel for destroyer hulls as it has a higher strength to weight ratio. But it is not armor. It resists stretching better but still has a bit of give. Even homogeneous armor can be too stiff for structural work and tend to crack. Hulls can do a fair amount of bending in a sea way. But even high tensile steel is much less resistant to penetration than real armor.

The U.S. had been reluctant to give up the 5"/51 used on some WW I destroyers and as battleship secondaries and go to the 5"/38. But even the French found they had trouble spotting the shell splashes of 5.5" guns with much heavier shells much past 13,000 meters from their super destroyers.
The extra range was pretty much an illusion unless you can find combat reports of destroyers actually hitting at 12,000 meters and above.