CLAA Tenryu - Design

[PaxMondo]

Ok, we know what the IJN did historically: they replaced 14cm/50 3YT with their standard 12.7 cm/40 (5") Type 89. A good weapon, nothing exceptional. Middling rate of fire and altitude. I suspect know why they went that way, but that isn't really the question.

Was this the best choice? Should they have gone for the 100mm/65 Type 98? Better altitude and ROF at about the same twin mount weight as the 14cm/50 3YT. Or maybe the 8 cm/60? Same altitude as the 12.7 cm/40 (5"), but much lighter and smaller and double the ROF? (Do you really need higher than 30,000 ft for naval AA in this era?)

Granted a 5" shell makes a much bigger boom, but is that preferred over twice as many 8cm booms for AA?

Looking for some "Naval Nutjobs" to weigh in here. This is design philosophy, from both a ship and desired AA effectiveness. Looking to arrive at the most effective CLAA design for AA as a CV support. All other roles are subordinate to that.

[Terminus]

The IJN wanted to arm the Tenryus with the 10cm gun, but the Akizuki class was given priority.

[PaxMondo]

Thanks Termy for this insight as to why they did what they did.
 
 

[PaxMondo]

Looking into the game a bit, it appears that AA ratings that you see on the ship display are essentially the sum of the effect of the AA guns * 50%.  So, if you go to either the 100/65 or 80/60 you will show less AA "power" than the 127/40.  However, in the ship gun info display, ROF is backed out and displayed.  So while the "power" is lower the ROF is higher.
 
So back to my call for some Naval Design Engr opinion: what would be your ideal gun choice 100/65, 80/60, or 127/40 for the Tennryu if your primary goal was AA protection for a CV?
 
Appreciate the thoughts.

[Terminus]

I wouldn't bother with the old cruisers. Scrap them and construct additional Akizukis.

[PaxMondo]

ORIGINAL: Terminus

I wouldn't bother with the old cruisers. Scrap them and construct additional Akizukis.

Yes, but in war you rarely scrap any ship. I'm trying to think of some examples and nothing comes to mind. I'm sure it was done, but gotta be rare. Something too old and slow to keep up is put into the training fleet. Tennryu aren't too slow, so they would stay in service during a war emergency. I think.

Anyway, for discussions sake, how would you arm them? And I'm only using the Tennryu as the exemplar. In fact, it would apply to all of the IJN CL's if you wanted them converted to CLAA ...

I guess my real question is 100/65 or 80/60? I understand the Aki's using the 100/65 because it really is a DP gun for them. But if I say that this is going to be a CLAA, and surface action firepower is no longer a concern (or very secondary to AA), what armament would you go with? Again the 127/45 is what was used historically, but is that really the best choice?

As I examine the data, the 80/60 looks best. In this era, I cannot see needed higher than 30,000 ft AA for naval forces. Given the weight involved you get 2 80/60 for each 127/45 or 100/65. That a significant increase in batteries. They also have almost double the ROF. BUT, a 127 shell has a lot more boom. So, back to my OP ... appreciate any and all insights into this. THANKS!

[herwin]

The Tenryus were top-heavy. I'm not sure you'd want to put guns on it too far above the waterline. Less, larger guns on the main deck might be better.

[Terminus]

ORIGINAL: PaxMondo

ORIGINAL: Terminus

I wouldn't bother with the old cruisers. Scrap them and construct additional Akizukis.

Yes, but in war you rarely scrap any ship. I'm trying to think of some examples and nothing comes to mind. I'm sure it was done, but gotta be rare. Something too old and slow to keep up is put into the training fleet. Tennryu aren't too slow, so they would stay in service during a war emergency. I think.

Anyway, for discussions sake, how would you arm them? And I'm only using the Tennryu as the exemplar. In fact, it would apply to all of the IJN CL's if you wanted them converted to CLAA ...

I guess my real question is 100/65 or 80/60? I understand the Aki's using the 100/65 because it really is a DP gun for them. But if I say that this is going to be a CLAA, and surface action firepower is no longer a concern (or very secondary to AA), what armament would you go with? Again the 127/45 is what was used historically, but is that really the best choice?

As I examine the data, the 80/60 looks best. In this era, I cannot see needed higher than 30,000 ft AA for naval forces. Given the weight involved you get 2 80/60 for each 127/45 or 100/65. That a significant increase in batteries. They also have almost double the ROF. BUT, a 127 shell has a lot more boom. So, back to my OP ... appreciate any and all insights into this. THANKS!

I'd scrap them before the war. However, for the sake of discussion, I'd do what the IJN did in real life, and use the 12.7cm. It saves the 10cm for the Akizukis and it has more explosive power than the 8cm.

[herwin]

ORIGINAL: Terminus

ORIGINAL: PaxMondo

ORIGINAL: Terminus

I wouldn't bother with the old cruisers. Scrap them and construct additional Akizukis.

Yes, but in war you rarely scrap any ship. I'm trying to think of some examples and nothing comes to mind. I'm sure it was done, but gotta be rare. Something too old and slow to keep up is put into the training fleet. Tennryu aren't too slow, so they would stay in service during a war emergency. I think.

Anyway, for discussions sake, how would you arm them? And I'm only using the Tennryu as the exemplar. In fact, it would apply to all of the IJN CL's if you wanted them converted to CLAA ...

I guess my real question is 100/65 or 80/60? I understand the Aki's using the 100/65 because it really is a DP gun for them. But if I say that this is going to be a CLAA, and surface action firepower is no longer a concern (or very secondary to AA), what armament would you go with? Again the 127/45 is what was used historically, but is that really the best choice?

As I examine the data, the 80/60 looks best. In this era, I cannot see needed higher than 30,000 ft AA for naval forces. Given the weight involved you get 2 80/60 for each 127/45 or 100/65. That a significant increase in batteries. They also have almost double the ROF. BUT, a 127 shell has a lot more boom. So, back to my OP ... appreciate any and all insights into this. THANKS!

I'd scrap them before the war. However, for the sake of discussion, I'd do what the IJN did in real life, and use the 12.7cm. It saves the 10cm for the Akizukis and it has more explosive power than the 8cm.

Did the 8cm have a timed fuse? That was needed for an effective barrage until the introduction of proximity fusing by the Americans.

[PaxMondo]

ORIGINAL: Terminus

I'd scrap them before the war. However, for the sake of discussion, I'd do what the IJN did in real life, and use the 12.7cm. It saves the 10cm for the Akizukis and it has more explosive power than the 8cm.

Interesting. Thanks for your insight. Much appreciated.

[PaxMondo]

ORIGINAL: herwin

The Tenryus were top-heavy. I'm not sure you'd want to put guns on it too far above the waterline. Less, larger guns on the main deck might be better.

Wasn't that a problem with several of the IJN designs?

[Terminus]

The Tenryus weren't top heavy.

[DBS]

The 8/60 Type 98 supposedly had a short barrel life of only around 600 rounds, compared to twice/thrice that for the 40 calibre models (and indeed the 127/40). That may have been a factor against it seeing wider service - a piddling number only were made after all. Maybe there were other issues of ease of manufacturing or cost-effectiveness?

EDIT - The real killer I am sure is that, looking at the Army's 8cm and 12cm AA weapons as approximate equivalents, the 12cm shell produced ten times the "volume of rupture" compared to the 8cm. So even allowing for the lower ROF, potentially five to six times more effective.

[herwin]

ORIGINAL: Terminus

The Tenryus weren't top heavy.

I stand corrected. Which was the light cruiser class that had to be reconstructed for this reason in the 1920s?

[PaxMondo]

ORIGINAL: DBS

The 8/60 Type 98 supposedly had a short barrel life of only around 600 rounds, compared to twice/thrice that for the 40 calibre models (and indeed the 127/40). That may have been a factor against it seeing wider service - a piddling number only were made after all. Maybe there were other issues of ease of manufacturing or cost-effectiveness?

EDIT - The real killer I am sure is that, looking at the Army's 8cm and 12cm AA weapons as approximate equivalents, the 12cm shell produced ten times the "volume of rupture" compared to the 8cm. So even allowing for the lower ROF, potentially five to six times more effective.

Thanks ... I was curious about that aspect.

[JWE]

ORIGINAL: herwin
Did the 8cm have a timed fuse? That was needed for an effective barrage until the introduction of proximity fusing by the Americans.

Yes. A settable time fuse is a necessary component of an AA round. Known for ages and everybody had them. One sticky point is that many nations called their ordinary settable time fuses ‘variable time’ fuses. So you will see hundreds of references to ‘VT’ fuses that were not the same thing as the radar proximity VT fuses we all know and love so well. [;)]

ORIGINAL: herwin
Which was the light cruiser class that had to be reconstructed for this reason in the 1920s?

None actually, Harry. They were all designed in the ‘teens and all laid down by 1922 – long before the insanity of the 1930 design plan. Some were reconstructed, but for other reasons (Kitikami, Oi, etc.).

[herwin]

ORIGINAL: JWE

ORIGINAL: herwin
Did the 8cm have a timed fuse? That was needed for an effective barrage until the introduction of proximity fusing by the Americans.

Yes. A settable time fuse is a necessary component of an AA round. Known for ages and everybody had them. One sticky point is that many nations called their ordinary settable time fuses ‘variable time’ fuses. So you will see hundreds of references to ‘VT’ fuses that were not the same thing as the radar proximity VT fuses we all know and love so well. [;)]

ORIGINAL: herwin
Which was the light cruiser class that had to be reconstructed for this reason in the 1920s?

None actually, Harry. They were all designed in the ‘teens and all laid down by 1922 – long before the insanity of the 1930 design plan. Some were reconstructed, but for other reasons (Kitikami, Oi, etc.).

Thanks.

The smaller calibre AA (40 mm on down) had percussion fuses. No touch; no bang.

[PaxMondo]

ORIGINAL: DBS

The 8/60 Type 98 supposedly had a short barrel life of only around 600 rounds, compared to twice/thrice that for the 40 calibre models (and indeed the 127/40). That may have been a factor against it seeing wider service - a piddling number only were made after all. Maybe there were other issues of ease of manufacturing or cost-effectiveness?

EDIT - The real killer I am sure is that, looking at the Army's 8cm and 12cm AA weapons as approximate equivalents, the 12cm shell produced ten times the "volume of rupture" compared to the 8cm. So even allowing for the lower ROF, potentially five to six times more effective.

Inspecting the device file, this is consistent. The 127/40 appears to be a far better weapon, roughly 6x better or even more, due to effect. I think I have my answer here now.

Thanks for the contributions!