AHC/WI: Stronger IJN light cruiser line

[Kantai Kessen]

The IJN's four-strong Mogami-class are probably the most blatant example of naval treaty violation in human history:

Mogami-class cruiser - Wikipedia

en.wikipedia.org

Originally they were armed with fifteen 6.1-inch guns in five triple turrets, with a max RoF of 5 rounds a minute (the powder hoists could not supply charges faster: http://www.navweaps.com/Weapons/WNJAP_61-60_3ns.php). These were later swapped out for ten 8-inch guns in five dual turrets, with a max RoF of 4 rounds a minute, turning the Mogamis into heavy cruisers.

However, this left the IJN with, to put it bluntly, a terrible light cruiser line that failed consistently to match up to Allied counterparts over the course of the Pacific War. Nagaras and Sendais were no match for the likes of a Brooklyn or Cleveland, and I've no doubt that if a Town or Crown Colony rocked up it would tear the Japanese ships a new one. I think it would be worthwhile if the IJN wised up to the potential of massed 6-inch firepower and beefed up their light cruiser line.

Your challenge, therefore, is to give the IJN a reason to keep the Mogamis as light cruisers after 1939, perhaps with the addendum that the shell and powder hoists are upgraded to allow for the theoretical max RoF of 7 rounds a minute (close enough to the 8 rounds a minute average of the US and British ships). How can this be done?

Once that has been accomplished, the role of these ships is undoubtedly going to be different. How do you see them being used in the Pacific War, and what impact could they have on various engagements?

EDIT: upon consideration and discussion, I don't think changing up the Mogamis will do much.

Here, therefore, is your new, wider challenge: give the IJN a reason and the ability to build Town/Brooklyn equivalents and have them ready to fight by August 1942. What happens next? You're allowed to cancel the Yamato-class and build smaller BBs if you think that will be necessary.

 

[RamscoopRaider]

The Light/Heavy Cruiser divide is pretty artificial, and the Japanese Terms for cruisers were A, B, C and D type if I remember correctly. Nagaras and Sendais weren't meant to fight enemy cruisers, they were meant to provide space for DD flag facilities for leading destroyers. The ships that were to replace them were supposed to do that and provide floatplane scouting for DD and SS squadrons. Fighting cruisers was for the larger types, doctrinally the Brooklyn or Cleveland or Town or Crown Colony should be too busy tangling with a Takao, Tone, Mogami or Myoko, or dying under a Kongo's guns, to target the Nagara/Sendai/Agano leading the destroyers

The easiest way is just to have the shipyards more congested so they can't spare the yard time to refit them.

The role is going to be exactly the same and functionally no real difference, still going to be doing floatplane scouts for larger formations, still going to be torpedo platforms for the night battle and to tangle with enemy crusiers during that. Only real difference is probably a different cruiser squadron is picked for bombardment at Midway, and Mogami's oops that led to the loss of Mikuma won't happen

 

[tomo pauk]

What do you intend to do with Mogamis that didn't received 8in guns?

 

[jsb]

The IJN's four-strong Mogami-class are probably the most blatant example of naval treaty violation in human history:

Not really sure if they are that bad a violation the dates they got bulged and swapped to 8" is far too late to matter as by then the treaties are falling apart are they not?

How are they worse than some other violations like USN CV 2/3 never making weight in 20s or some of the earlier European ships?

 

[Kantai Kessen]

What do you intend to do with Mogamis that didn't received 8in guns?

I was thinking that, first of all, they wouldn't be chosen for the Midway bombardment. Thus all four ships would survive the 1st half of 1942 and be available for the Guadalcanal campaign. With their rapid-firing, high-power 6.1-inch guns, they would be great for the brawls that resulted in Ironbottom Sound. In such close quarters, volume of fire counts for more than shell weight and range, and the 6.1-inch guns fire heavy enough shells in those conditions anyway.

 

[Kantai Kessen]

Not really sure if they are that bad a violation the dates they got bulged and swapped to 8" is far too late to matter as by then the treaties are falling apart are they not?

How are they worse than some other violations like USN CV 2/3 never making weight in 20s or some of the earlier European ships?

Saying that they were only 8500 tonnes at the time of construction was, IMO, a bit far. So much so that the British Director of Naval Construction, when he saw the reported figures alongside the reported performance, said that the IJN either had to be lying or building their ships out of cardboard.

Also, designing them from the start to switch out to 8-inch guns showed that the IJN intended to cheat from the start, even when the treaty system was still in effect.

 

[CV12Hornet]

I was thinking that, first of all, they wouldn't be chosen for the Midway bombardment. Thus all four ships would survive the 1st half of 1942 and be available for the Guadalcanal campaign. With their rapid-firing, high-power 6.1-inch guns, they would be great for the brawls that resulted in Ironbottom Sound. In such close quarters, volume of fire counts for more than shell weight and range, and the 6.1-inch guns fire heavy enough shells in those conditions anyway.

Okay, but when? Early on the Japanese are scrambling to get forces into the area and the 6-gun heavy cruisers have the great advantage of being already in the combat area. By the time November rolls around the job is mainly bombardment duties and just as with Midway that's going to be a task the Japanese select cruisers with 8" guns for.

I just don't see much of an opportunity for them to fight anything in Ironbottom Sound.

 

[Kantai Kessen]

Okay, but when? Early on the Japanese are scrambling to get forces into the area and the 6-gun heavy cruisers have the great advantage of being already in the combat area. By the time November rolls around the job is mainly bombardment duties and just as with Midway that's going to be a task the Japanese select cruisers with 8" guns for.

I just don't see much of an opportunity for them to fight anything in Ironbottom Sound.

I don't know if this is a good idea, but I was thinking that Mikawa's 8th Fleet, when first formed, could be assigned a pair of 6.1-inch Mogamis instead of the Chokai; the CA would be instead kept with her sisters in CruDiv4 to give 2nd Fleet a full-strength unit of heavy cruisers.

Going back to Midway, this is how the twelve 10-gun and two 8-gun CAs were disposed OTL:

• Tone, Chikuma (RAdm Abe): escorting Kido Butai
• Mogami, Mikuma, Suzuya, Kumano (VAdm Kurita): bombardment force
• Atago, Chokai (VAdm Kondo), Myoko, Haguro (VAdm Takagi): invasion force
• Nachi, Takao, Maya (VAdm Hosogaya): Operation AL
• Ashigara: refit in Japan

With the Mogami Lights, what I'd do is this:

• Tone, Chikuma (RAdm Abe): escorting Kido Butai
• Myoko, Haguro, Takao, Maya (VAdm Takagi): bombardment force
• Atago, Chokai (VAdm Kondo), Suzuya, Kumano (VAdm Kurita): invasion force
• Nachi, Mogami, Mikuma (VAdm Hosogaya): Operation AL
• Ashigara: refit in Japan

This would prevent Mogami and Mikuma getting murked in an air attack and thus make them available for late 1942. Give them to 8th Fleet in place of a more precious 8-inch cruiser that won't do well in the shallow and confined Solomons anyway. Hoisting his flag on Mikuma, Mikawa can then hand the US their defeat at Savo Island with 2 big light cruisers and 4 old heavy cruisers. In fact, the larger number of guns and torpedo tubes may do in Chicago as well.

Thoughts?

 

[CV12Hornet]

I don't know if this is a good idea, but I was thinking that Mikawa's 8th Fleet, when first formed, could be assigned a pair of 6.1-inch Mogamis instead of the Chokai; the CA would be instead kept with her sisters in CruDiv4 to give 2nd Fleet a full-strength unit of heavy cruisers.

Going back to Midway, this is how the twelve 10-gun and two 8-gun CAs were disposed OTL:

• Tone, Chikuma (RAdm Abe): escorting Kido Butai
• Mogami, Mikuma, Suzuya, Kumano (VAdm Kurita): bombardment force
• Atago, Chokai (VAdm Kondo), Myoko, Haguro (VAdm Takagi): invasion force
• Nachi, Takao, Maya (VAdm Hosogaya): Operation AL
• Ashigara: refit in Japan

With the Mogami Lights, what I'd do is this:

• Tone, Chikuma (RAdm Abe): escorting Kido Butai
• Myoko, Haguro, Takao, Maya (VAdm Takagi): bombardment force
• Atago, Chokai (VAdm Kondo), Suzuya, Kumano (VAdm Kurita): invasion force
• Nachi, Mogami, Mikuma (VAdm Hosogaya): Operation AL
• Ashigara: refit in Japan

This would prevent Mogami and Mikuma getting murked in an air attack and thus make them available for late 1942. Give them to 8th Fleet in place of a more precious 8-inch cruiser that won't do well in the shallow and confined Solomons anyway. Hoisting his flag on Mikuma, Mikawa can then hand the US their defeat at Savo Island with 2 big light cruisers and 4 old heavy cruisers. In fact, the larger number of guns and torpedo tubes may do in Chicago as well.

Thoughts?

Do you know why Chokai was assigned to Mikawa's Eighth Fleet? And in fact why the Takao-class had largely operated in company with other classes of heavy cruiser instead of each other?

They were flagships. Everywhere they went they were what the local admiral raised his flag in thanks to their massive bridge structures. Well, except for Midway, but that was an all-hands-on-deck situation.

The point being, with Japan's heavy cruisers scattering to the four winds again after Midway, they'll want to assign a Takao to Mikawa's force to act as a flag vessel.

I should also note that the Japanese won't consider the 155mm cruisers to be superior in confined night actions. After all, the heavy cruisers were designed precisely for such actions as part of the Night Battle phase of the Kantai Kessen plan. Even the US Navy didn't decide their 6" cruisers were the better option in that case until after the Guadalcanal campaign concluded, and after four cruiser-destroyer actions.

 

[Kantai Kessen]

Do you know why Chokai was assigned to Mikawa's Eighth Fleet? And in fact why the Takao-class had largely operated in company with other classes of heavy cruiser instead of each other?

They were flagships. Everywhere they went they were what the local admiral raised his flag in thanks to their massive bridge structures. Well, except for Midway, but that was an all-hands-on-deck situation.

The point being, with Japan's heavy cruisers scattering to the four winds again after Midway, they'll want to assign a Takao to Mikawa's force to act as a flag vessel.

I should also note that the Japanese won't consider the 155mm cruisers to be superior in confined night actions. After all, the heavy cruisers were designed precisely for such actions as part of the Night Battle phase of the Kantai Kessen plan. Even the US Navy didn't decide their 6" cruisers were the better option in that case until after the Guadalcanal campaign concluded, and after four cruiser-destroyer actions.

I thought the main weapon of the Night Battle was going to be the Long Lance, not the 8" gun? Worth noting that Mogamis have 12 Type 93 torpedo tubes; Chokai was never refitted fully like her sisters and so only had 8 for her entire career. Maya has not yet been refitted. However, point taken about flag capabilities. I hadn't considered that.

TBH, Chokai is my favourite CA of all time, so on 2nd thoughts I'd rather let her have her glory.

Do you think you could arrange it so that CruDiv6 (Goto - old CAs) and CruDiv7 (Kurita - big CLs) switch places? Technically, CruDiv6 is a CA unit, so they would higher up in prestige and thus potentially could be used in the positions that CruDiv7 filled OTL.

 

[Kantai Kessen]

They were flagships. Everywhere they went they were what the local admiral raised his flag in thanks to their massive bridge structures. Well, except for Midway, but that was an all-hands-on-deck situation.

Well, even there too. Kondo hoisted his flag on Atago, as he had done for the entire war until then and would do so until he got Kimmeled after Guadalcanal.

 

[CV12Hornet]

I thought the main weapon of the Night Battle was going to be the Long Lance, not the 8" gun? Worth noting that Mogamis have 12 Type 93 torpedo tubes; Chokai was never refitted fully like her sisters and so only had 8 for her entire career. Maya has not yet been refitted. However, point taken about flag capabilities. I hadn't considered that.

TBH, Chokai is my favourite CA of all time, so on 2nd thoughts I'd rather let her have her glory.

Do you think you could arrange it so that CruDiv6 (Goto - old CAs) and CruDiv7 (Kurita - big CLs) switch places? Technically, CruDiv6 is a CA unit, so they would higher up in prestige and thus potentially could be used in the positions that CruDiv7 filled OTL.

Long Lances were the main weapon, but the CAs were aimed at the American cruiser screen, not the battleships, and even at their most optimistic about long-range torpedo salvoes the Japanese expected their cruisers to have to close into gun range to finish the job. Savo Island is a pretty good demonstration that they were probably right about that. Regardless, even if Long Lances were the sole weapon that just emphasizes that any real difference in effectiveness between 8" and 155mm main batteries is fairly academic for the Japanese.

Doubt it. CruDiv 6's ships are small, old, and armed with only 6 guns. They were kept largely to secondary duties through the first half of 1942, and even with the Mogamis rocking 155mm guns I don't think that'll change. As an example, I think the Japanese would much prefer to take the 155mm Mogamis on the Indian Ocean raid over the Furutakas and Aobas.

 

[Jellico]

Your challenge, therefore, is to give the IJN a reason to keep the Mogamis as light cruisers after 1939, perhaps with the addendum that the shell and powder hoists are upgraded to allow for the theoretical max RoF of 7 rounds a minute (close enough to the 8 rounds a minute average of the US and British ships). How can this be done?

There is your problem. Slow rate of fire compared to the Allied ships.


You need to remember why the 8" gun was chosen. In the Pacific you can see a long way and the 8" is a superior gunnery weapon to the 6". No one really saw gun fights at short range as a thing. That was what torpedoes were for. Does a 6" machinegun even work as a weapons platform without radar?

 

[Kantai Kessen]

There is your problem. Slow rate of fire compared to the Allied ships.


You need to remember why the 8" gun was chosen. In the Pacific you can see a long way and the 8" is a superior gunnery weapon to the 6". No one really saw gun fights at short range as a thing. That was what torpedoes were for. Does a 6" machinegun even work as a weapons platform without radar?

I see the issue. OK.

I think I'm gonna have to rename the thread.

 

[Kantai Kessen]

Thread has been renamed and has a new purpose: see post 1.

 

[CalBear]

I was thinking that, first of all, they wouldn't be chosen for the Midway bombardment. Thus all four ships would survive the 1st half of 1942 and be available for the Guadalcanal campaign. With their rapid-firing, high-power 6.1-inch guns, they would be great for the brawls that resulted in Ironbottom Sound. In such close quarters, volume of fire counts for more than shell weight and range, and the 6.1-inch guns fire heavy enough shells in those conditions anyway.

They might all survive, however, all that means is that they are replaced, probably by the Takao class* ships of CruDiv 4. Same scenario, just different ship names.

Rapid firce shell weight is more important if it is actually rapid. 10 rounds/min, which the American 6"/47 could maintain for the length of a battle, is able to saturate a target (especially when the "super-heavt" AP round performs at close to regular 8"AP round penetration levels). That calculation, however, changes dramatically when the conversation is between 4-5 rounds/min for 15.5cm and 3-4 rounds/min for 20cm. In this case the superior throw weight and much better armor penetration/heavier bursting charge more than compensates for the lower rate of fire.

*When talking about cheating tonnages, the Takao are right near the top of the contender list. While the Mogamis, in 20 cm form, came in at ~13,400 tons (34.4% over Treaty limits), the Takaos weighed in at ~15,800 tons (58% over Treaty cap) with the Myoko class also ahead of the Mogamis at ~15,000 tons (nice even 50% over cap). In the "if you ain't cheatin' you ain't tryin'" comparison the Mogami class comes in a distant 3rd.

The Takao and Myoko classes both came in at tonnages over the KM's Deutschland class panzerschiffe (14,290 tons)

All IJN tonnages from Combined Fleet.com

 

[RamscoopRaider]

Different LNT, instead of a Heavy/Light cruiser divide, there is a small and large, a limited number of cruisers over say 6,000 tons are allowed, but an unlimited number under that are. As a result instead of 9 10,000 ton CLs, the US builds ~15 4,000 ton scout cruisers/super destroyers, while the Japanese move up some of their late 30's smaller cruiser construction to replace the Mogamis in the que. Come the Japanese exit of the treaty system and in addition to the US heavies to worry about, there are a bunch of smaller ships too large for the destroyers to deal with. As such the *Mogami's are built with the intention of being armed with 15 rapid firing 155mm guns, the option of replacing them with larger guns is still designed into them in case the situation changes, but they are needed to counter US scout cruisers at first

They might all survive, however, all that means is that they are replaced, probably by the Takao class* ships of CruDiv 4. Same scenario, just different ship names

The argument is without Mogami's horrible shiphandling causing that collision, their equivalents would be able to escape Midway without being bombed as they can withdraw at full speed

 

[Kantai Kessen]

Different LNT, instead of a Heavy/Light cruiser divide, there is a small and large, a limited number of cruisers over say 6,000 tons are allowed, but an unlimited number under that are. As a result instead of 9 10,000 ton CLs, the US builds ~15 4,000 ton scout cruisers/super destroyers, while the Japanese move up some of their late 30's smaller cruiser construction to replace the Mogamis in the que. Come the Japanese exit of the treaty system and in addition to the US heavies to worry about, there are a bunch of smaller ships too large for the destroyers to deal with. As such the *Mogami's are built with the intention of being armed with 15 rapid firing 155mm guns, the option of replacing them with larger guns is still designed into them in case the situation changes, but they are needed to counter US scout cruisers at first

The argument is without Mogami's horrible shiphandling causing that collision, their equivalents would be able to escape Midway without being bombed as they can withdraw at full speed

I think 6,000 tons is a bit low. The US already had the 7,600-tonne standard Omaha-class which were already scout cruisers, and which were very unsatisfactory. The British Arethusa-class came in around 4800 tonnes standard, but they were mainly for trade protection and the DesRon flagship role. The IJN's later and similar Agano-class came in at 6700 tonnes standard.

Interesting idea though. Will consider.

 

[tomo pauk]

@Kantai Kessen - do we still have IJN cheating on tonnage here? Answer to that has a lot of bearing on how the alternative cruiser line looks like.

 

[RamscoopRaider]

I think 6,000 tons is a bit low. The US already had the 7,600-tonne standard Omaha-class which were already scout cruisers, and which were very unsatisfactory. The British Arethusa-class came in around 4800 tonnes standard, but they were mainly for trade protection and the DesRon flagship role. The IJN's later and similar Agano-class came in at 6700 tonnes standard.

Interesting idea though. Will consider.

Yes the US has the Omaha, but the Omaha is a large scout cruiser and the forerunner of the 10,000 8" Treaty cruisers

The Arethusa being under 6,000 tons is why I chose that number, the British want to build A LOT of those type of ships and don't want a lot of ships that can overpower them around. The 1st Gen Condotierri class cruiser are under 6,000 tons, as is Emile Bertin and all the then current Japanese small cruisers. That said maybe 6500 tons to fit Jean d'Arc in or 7,000 so the Italians can cheat less on the latter examples