IJN AA cruisers

[ceccherini]

Japanese Wikipedia entry on Akizuki class DD stated that IJN started in 1936 to study dedicated AA vessels following the example of Dido class. They contemplated anything from a 1000 ton torpedo boat armed with a single 10 cm or 12.7 cm AA gun to a quite large cruiser equipped with 12 double 10cm/65 mounts, with serious consideration on converting part of the existing 5500 ton type light cruisers rearming them with 12,7cm/40. Akizuki was the result of this requirement, it's size and gun number being considered the best choice for optimal distribution of the fleet's AA capabilities. By 1941 a new class of AA cruisers was being considered: this cruisers, no.815-818, were not intended to offer a complementary higher end AA capability but only to serve as sort of command ship for Akizuki class DD. Has anyone any more information and pictures of this various projects?

 

[Tzoli]

That one drawing is probably the first artist impression of the proposal of the AA cruiser

Oyodo's hull was capable to hold such large amount of guns as my drawing suggests:

The Anti Aircraft Oyodo by Tzoli on DeviantArt

www.deviantart.com

And in Japanese Cruisers of the Pacific war by Eric Lacroix states as follows:



Super Type A cruisers: The battlecruisers or large cruisers of the B-65 class intended to counter the USN's Alaska class which in fact intended to counter partly the German Deutschlands but mostly the fake Chichibu class big gun cruisers.
Type A cruisers: Heavy cruisers of 203mm Guns
Type B cruisers: Destroyer squadron leaders of the Agano and Kai-Agano class
Type C cruisers: Submarine squadron leaders of the Oyodo class

 

[Tzoli]

And the Japanese wiki article about the four CLAA:

815号型軽巡洋艦 - Wikipedia

ja.wikipedia.org

 

[JFC Fuller]

The V18 design AA cruisers were intended to be 5,800 tons standard with 4 x 2 10cm HA guns. I assume there would have been two Type 94 HA directors for fire control. Beyond that the only reason I can think for them getting to be so much larger than the Akizuki class is the addition of Agano style Torpedo (2 x 4 tubes) and catapult (1 x 26m) along with more protection and endurance. They were to have formed their own Sentai and were therefore not leaders for Akizuki DesRons.

The 24 x 10cm gun cruiser was a proposal for converting (during construction) Oyodo and Niyodo, made sometime around 1938-1939. IMO it would have made them much more useful ships but would have increased demand for the 10cm guns and mountings. It doesn't seem to have been an idea that was take particularly seriously though. Looking at the plans of Oyodo I think it would have been hard to convert the ship to the configuration shown above unless she had been in the very early stages of construction, her wing 10cm guns were open backed and had their own magazine space, additional magazine space could only have been found where the 15cm magazines were and in the bomb shed under the hangar. Also, that configuration shows no aviation facilities which would be unique for a Japanese cruiser design of this period.

 

[Tzoli]

Some time ago I made various layouts which I deem possible for the arrangement of the 12 twin mounts on the Oyodo hull:

 

[Foo Fighter]

Just a thought, how long could the stores of ammunition allow sustained fire in a saturation attack? Not that long imho.

 

[Hood]

Yes the internal layout would dictate the turret locations, not to mention the topweight.
I don't think its necessarily true that the centreline arrangements would be symmetrical fore and aft. Given the relative blank canvas the rear portion of the ship is once the aviation facilities are removed more guns may of been intended aft that forewards. Likewise two beam mounts per side feels the likely maximum.

I have some doubts about the drawing ceccherini posted, I think this was from a (1980s?) Japanese magazine in an article on the unbuilt cruisers. Some of the other drawings in that article have been deemed to be speculative at best.

 

[ceccherini]

Lacroix pretty much confirms what I wrote above but for added context:

The V18 design AA cruisers were intended to be 5,800 tons standard with 4 x 2 10cm HA guns. I assume there would have been two Type 94 HA directors for fire control. Beyond that the only reason I can think for them getting to be so much larger than the Akizuki class is the addition of Agano style Torpedo (2 x 4 tubes) and catapult (1 x 26m) along with more protection and endurance. They were to have formed their own Sentai and were therefore not leaders for Akizuki DesRons.

Also confirms that the 24 x 10cm gun cruiser was a proposal for converting (during construction) Oyodo and Niyodo, made sometime around 1938-1939. IMO it would have made them much more useful ships but would have increased demand for the 10cm guns and mountings. It doesn't seem to have been an idea that was take particularly seriously though. Looking at the plans of Oyodo I think it would have been hard to convert the ship to the configuration shown above unless she had been in the very early stages of construction, her wing 10cm guns were open backed and had their own magazine space, additional magazine space could only have been found where the 15cm magazines were and in the bomb shed under the hangar. Also, that configuration shows no aviation facilities which would be unique for a Japanese cruiser design of this period.

But Oyodo was finalized in late 1939 if I remember correctly. In late 1938 they were still undecided about building a light carrier, a cruiser-carrier or the Oyodo as actually built to satisfy the requirement. It's doubtfull they consider the convertion of a ship that was not even fully designed. If this was the case why not make a dedicated project from the ground up? Maybe they were contemplating a new project based on a hull derived by agano/oyodo, as the speculated Japanese "Atlanta" was always reported to be in the various publications that made mention of it.

 

[ceccherini]

That one drawing is probably the first artist impression of the proposal of the AA cruiser

Oyodo's hull was capable to hold such large amount of guns as my drawing suggests:

The Anti Aircraft Oyodo by Tzoli on DeviantArt

www.deviantart.com

And in Japanese Cruisers of the Pacific war by Eric Lacroix states as follows:
View attachment 619150
View attachment 619149
View attachment 619151
Super Type A cruisers: The battlecruisers or large cruisers of the B-65 class intended to counter the USN's Alaska class which in fact intended to counter partly the German Deutschlands but mostly the fake Chichibu class big gun cruisers.
Type A cruisers: Heavy cruisers of 203mm Guns
Type B cruisers: Destroyer squadron leaders of the Agano and Kai-Agano class
Type C cruisers: Submarine squadron leaders of the Oyodo class

Wonderful drawings, really actractive designs expecially the first and the second

 

[Tzoli]

Well oyodo ordered in 1939, laid down in 1941 February, launched 1942 April and finished in 1943 February so a project in 1941 to finish her as a CLAA wasn't out of practicality as in mid 1941 the hull might sufficiently incomplete to be finished to such a modified design.
And here is her internal layout:

 

[JFC Fuller]

But Oyodo was finalized in late 1939 if I remember correctly. In late 1938 they were still undecided about building a light carrier, a cruiser-carrier or the Oyodo as actually built to satisfy the requirement. It's doubtfull they consider the convertion of a ship that was not even fully designed. If this was the case why not make a dedicated project from the ground up? Maybe they were contemplating a new project based on a hull derived by agano/oyodo, as the speculated Japanese "Atlanta" was always reported to be in the various publications that made mention of it.

We can only speculate but I can imagine a scenario whereby the IJN had money for the ships approved, materials were about to be ordered and slots on slipways were identified when someone who was (rightly) unconvinced of the concept decided to see if those resources could be put to better use. Either way, it never seems to have been a very serious proposal.

Like Hood I have concerns about the image in the first post:

1) I see no reason why the fore-most and aft-most turrets are raised one deck above the flush-deck hull, if anything it would increase issues with top weight
2) The big gaps between the aft and foremost turrets and those directly behind them also make little sense - three closely located turrets like a Dido would be more logical
3) As mentioned previously, the absence of torpedo gear (especially) and aircraft facilities is also very unusual for a Japanese cruiser of this era
4) Director layouts, I see no reason for these to be all centreline, one on either beam (as in Oyodo as built) and one fore and one aft in the usual locations again seems more likely

I suspect @Tzoli layout I/1 above would have been the most likely configuration based on the existing internal layout of the Oyodo class and general Japanese practice - depending how far construction had advanced when the switch was considered. It may not be the most efficient arrangement from a gun direction perspective though.

 

[Tzoli]

For torpedoes and Aircraft:
For a dedicated AA cruiser, torpedoes would be not of much use as it's mission was fleet AA defence and not night torpedo attack on enemy fleet,s though that many 10cm guns would devastate any destroyer and would be a menace to cruiser if it could get in range.
For aircraft the facilities which the IJN adopted: The midship catapults would take up precious space for AA armament and again AA defence does not require scouting and spotting.

 

[JFC Fuller]

For torpedoes and Aircraft:
For a dedicated AA cruiser, torpedoes would be not of much use as it's mission was fleet AA defence and not night torpedo attack on enemy fleet,s though that many 10cm guns would devastate any destroyer and would be a menace to cruiser if it could get in range.
For aircraft the facilities which the IJN adopted: The midship catapults would take up precious space for AA armament and again AA defence does not require scouting and spotting.

I don't buy this. The Akizukis were designed to provide AA defence to carrier groups and ended up with torpedos, the Japanese generally put them on everything. Similarly Japanese doctrine emphasised the use floatplanes for reconnaissance - even if not for the ship actually carrying them. I am less concerned by the lack of aircraft but the lack of torpedos and some of the other design features are quite suspect.

 

[Tzoli]

A different artist's interpretation (When Google Sketchup was a thing)

https://www.pixiv.net/member_illust.php?mode=medium&illust_id=39618007

https://www.pixiv.net/member_illust.php?mode=medium&illust_id=65092926

from a different artist:

https://www.pixiv.net/member_illust.php?mode=medium&illust_id=30596178

Other artists interpretations:

https://www.pixiv.net/member_illust.php?mode=medium&illust_id=70796330

https://www.pixiv.net/member_illust.php?mode=medium&illust_id=71574814

https://www.pixiv.net/member_illust.php?mode=medium&illust_id=46695434

https://www.pixiv.net/member_illust.php?mode=medium&illust_id=33539866

And the most likely interpretation of the 815 class of the Agano sized CLAA:

https://www.pixiv.net/member_illust.php?mode=medium&illust_id=7111140

 

[ceccherini]

But Oyodo was finalized in late 1939 if I remember correctly. In late 1938 they were still undecided about building a light carrier, a cruiser-carrier or the Oyodo as actually built to satisfy the requirement. It's doubtfull they consider the convertion of a ship that was not even fully designed. If this was the case why not make a dedicated project from the ground up? Maybe they were contemplating a new project based on a hull derived by agano/oyodo, as the speculated Japanese "Atlanta" was always reported to be in the various publications that made mention of it.

We can only speculate but I can imagine a scenario whereby the IJN had money for the ships approved, materials were about to be ordered and slots on slipways were identified when someone who was (rightly) unconvinced of the concept decided to see if those resources could be put to better use. Either way, it never seems to have been a very serious proposal.

Like Hood I have concerns about the image in the first post:

1) I see no reason why the fore-most and aft-most turrets are raised one deck above the flush-deck hull, if anything it would increase issues with top weight
2) The big gaps between the aft and foremost turrets and those directly behind them also make little sense - three closely located turrets like a Dido would be more logical
3) As mentioned previously, the absence of torpedo gear (especially) and aircraft facilities is also very unusual for a Japanese cruiser of this era
4) Director layouts, I see no reason for these to be all centreline, one on either beam (as in Oyodo as built) and one fore and one aft in the usual locations again seems more likely

Clearly it is a speculative drawing, still the turrets raising make sense to me: splashes interferences are reduced without the displacement penalties of an equivalent increase of the freeboard. Also distancing the turrets improve the firing arc, Worcester was similar but with much longer guns, so I didn't see a problem with it even in a shorter hull. Also Mogami had a similar disposition, so it is historically plausible. But yes, the absence of a floatplane carrying capability seems not very plausible. For torpedos: the actual Oyodo hadn't them while intended as a surface combatant, I would be surprised if they put them in an AA conversion or in an AA derivate.

 

[JFC Fuller]

Clearly it is a speculative drawing, still the turrets raising make sense to me: splashes interferences are reduced without the displacement penalties of an equivalent increase of the freeboard. Also distancing the turrets improve the firing arc, Worcester was similar but with much longer guns, so I didn't see a problem with it even in a shorter hull. Also Mogami had a similar disposition, so it is historically plausible. But yes, the absence of a floatplane carrying capability seems not very plausible. For torpedos: the actual Oyodo hadn't them while intended as a surface combatant, I would be surprised if they put them in an AA conversion or in an AA derivate.

The issue for me is the contradiction; if the design objective is to reduce the length of the armoured box then closely spaced/all superfiring turrets make sense, but they come with the downside of added top weight (CoG problems). If top weight is going to be a problem (e.g. on a ship with heavy turrets like the Worcester class) then the Mogami/Ibuki layout makes sense. The picture in the first post combines the worst of both layouts, a long armoured magazine length but with the entire armament pushed up a deck and therefore negatively impacting top weight (and increasing the amount of armour needed to cover the additional vertical surfaces). Furthermore, there never seems to have been an issue with the Oyodo or the Akizuki's having spray impact their foremost turrets thus rendering this suggested layout seemingly unnecessary.

 

[MJBurmaster]

Also, JFC, I seriously doubt having the heavy AA mounts on the beam ends given the impact on handling, especially with inclination. At best single rifle mounts with open backs. At least with midships alignment the effect on the ship's handling is lessened once you lose weuight deep down when you deplete the magazines.

 

[ptdockyard]

Skokatu Escort cruisers no.815-818 (V18 design): Apparently intended as leaders for Akizuki groups with additional flag facilities and some seaplanes and catapult

Does anyone have a drawing for this one? I have never heard of it before.

Dave G

 

[Tzoli]

That is the true CLAA design from start. Think of it as mixing the Akizuki with the Agano:
4x2 10cm, Catapult for seaplanes, probably torpedoes and probably optional DC. Hull most likely the same size as Agano

 

[able]

 

[Tzoli]

The turrets look too spherical for the 10cm Type 98 Guns, otherwise nice models

 

[able]

The turrets look too spherical for the 10cm Type 98 Guns, otherwise nice models

One is 10cm Type 98 Guns, the other is 12.7cm Type 89 Guns

 

[Dilandu]

Well oyodo ordered in 1939, laid down in 1941 February, launched 1942 April and finished in 1943 February so a project in 1941 to finish her as a CLAA wasn't out of practicality as in mid 1941 the hull might sufficiently incomplete to be finished to such a modified design.
And here is her internal layout:

Thank you for the plan! I'm toying with the idea of AU-Oyodo refitted as a missile cruiser for adapted Funryu-2 SAM system -



- and those blueprints are very helpful.

 

[Torsionbar]

This is "New type of AA ship". Ship No.815 has no pictures ，with eight 10cm guns.

 

[Tzoli]

This is "New type of AA ship". Ship No.815 has no pictures ，with eight 10cm guns.

Not exactly. The No.815-818 ships were to be CLAA Destroyer leaders to lead Akizuki class destroyer squadrons. These would had 4 twin 10cm turrets, catapult(s) extensive flag facillities and likely torpedo tubes. Sort of AA Oriented Aganos.
The drawing you posted is a different sketch for the conversion of the then under construction IJN Oyodo into a heavy AA ship as evident with the large number of 10cm twin turrets.

 

[Torsionbar]

不完全是。815-818号舰艇将成为CLAA号驱逐舰的领导者，领导Akizuki级驱逐舰中队。这些将有4个双10厘米炮塔，弹射器，广泛的旗帜设施和可能的鱼雷发射管。有点像AA制的Aganos。
你张贴的图纸是一个不同的草图，用于将当时正在建造的IJN奥约多号改造成重型AA船，这一点从大量的10厘米双炮塔可以明显看出。

This design is ealier than Akizuki class, the hull size is different to Oyodo, the view in 《Japanese Cruisers of the Pacific War》 is inaccurate.

 

[Torsionbar]

Not exactly. The No.815-818 ships were to be CLAA Destroyer leaders to lead Akizuki class destroyer squadrons. These would had 4 twin 10cm turrets, catapult(s) extensive flag facillities and likely torpedo tubes. Sort of AA Oriented Aganos.
The drawing you posted is a different sketch for the conversion of the then under construction IJN Oyodo into a heavy AA ship as evident with the large number of 10cm twin turrets.

The description of Shizuo Fukui is that the hull form of "New type of AA ship" is similar to Oyodo, rather than being modified by Oyodo.