Warship no. 300/301 Class A Cruiser "Ibuki"

[Azumazi]

Japan was to have during her 4th Replenishment Program up to the 6th newer cruisers to join with the carrier fleets as support ships. One of those that was in production was the Ibuki. During the thread of the Tone, someone mentioned the ship so I figured I would give a good background of what this ship is/was and what she was suppose to be.

 

The Ibuki, known as the W-103 Model, when she was in design, was to be a 13000 Ton Warship. She was being designed with modifications to the Mogami class to make her a true A class, taking issues of the past starting with the Myoko up to the Tone and correct design flaws and or improve upon features they felt were required. Unfortunately she was to be changed later in her design into a CV due to the events at Midway.

 

She was to be designed as based off the Suzuya class Mogami's, with stronger hull design, since she wasn't trying to stay within the 10000 ton limit, she didn't have nearly the issues the Mogami classes were having and it was in hindsight probably what they should have done for the Mogami class to begin with instead of what they did overall.

 

 

Her trial weight was to be 13890t with a full load of 14828 Tons, making her one of the heaviest A class Cruisers in the fleet. Her main guns were to be the same Type 3 50 cal no.2 20cm guns in twin turrets of E type Model turrets of the Tone Class, with one exception, they used vertical turret rings instead of conical ones due tot he winder 5.03m rollers. This allowed her to hold more armor should they want to and possibly allow a larger caliber gun, and by caliber I mean length of the 8 inch guns. Turrets 3 and 4 were to be equipped with Type 93 8m Duplex rangefinders.

 

 

Her armor was to be mostly like the Suzuya, Machinery spaces had belt protection of 100mm of NVNC Steel at a 20 degree inward angle, tapering to 30mm at the very low sections into the bottom hull to also double as an additional protection behind the bulge against torpedos. The lower 30mm was of CNC Steel. The Deck was 30mm of CNC steel in its flat locations to 60mm angled at the edges near the belt. The magazines were protected with 140mm of NVNC Steel at a slope of 20 degrees at the top to 30mm on the double bottom of the hull. It was protected by a 40mm armored deck angled with the turrets. The machinery spaces were enclosed by a reinforced bulkhead of 105mm of NVNC Steel to protect it from the bow and aft sections of the ships being unarmored.

 

The original turrets were to be 25mm of NVNC Steel with a 10 cm gap to the 2mm steel sheeting inside to provide an air buffer for tropical climate; however, the turrets and barberettes were designed to be able to hold up to 252 tons, which is 77 tons over the 175 tons of the original turrets (This section is where there is a lot of disagreements between some Japanese and English scholars).

 

In 1937, the Myoko was originally designed to have a much heavier turret with armor of 5.9 inches forward, 50mm sides and rear, and 100mm top, however the Myoko was already top heavy and the turrets when used would have caused the same issue the Mogami had with her turrets warping the hull on firing. The Ibuki with its reinforced bulkheads and redesigned internal hull was supposedly capable of holding these heavier turrets without fear of warping the deck/hull on use or issues with training the guns. During occupation of Japan, there were plans found of the turrets to be upgraded on the E types, and some work had been done, problem was there was no evidence found if they had been used or upgraded on the ships, some Japanese say the only ship to be tried with them was the Mogami herself on her 1944 third refit since the Ibuki was converted into a CV, and the loss of the 2 rear turrets afforded her the weight stress on the hull.

 

In the book Japanese Cruisers of WW2 by Lacroix and Wells-II, they excluded that data due to lack of overall evidence and the fact that they couldn't verify it. They admitted the plans for the Myoko were done and designed, but the upgraded turrets for the later A classes couldn't be verified.

 

Ibuki was also upgraded on her Torpedo armament. Instead of triple tubes in dual mounts on each side, she was to be upgraded to quads. With an armament of 16 torpedos with 8 reserve on rollers to reload the tubes for a second wave on each side. Also before she was to be launched, they debated removing the aircraft launchers to install 5, yes 5 quintuple torpedo tubes with 2 on each side and one in the centerline to allow 15 torpedos a broadside (Basically the Shimakaze's Torpedo turrets)

 

End Data

Weight: 13890 / 14828 Tons

Size:   Beam:  20.2m

Length: 198.35m

Draught: 6.07m (Estimated)

 

Speed: 35kt (10000nm at 13 knots) Estimated (Carrier got different speeds/range due to change in boilers)

 

Armament: 10 x 20cm Type 3 No.2 50-cal guns in dual turrets.

  8 x 127mm Type 89 40-cal High Angle guns in twin mounts

  8 x 25mm  Type 96 Machineguns in dual mounts

  4 x 13mm Type 93 Machineguns in dual mounts on the Bridge

  16 x Type 93 Long Lance torpedo launchers in quad mounts with 8 in reserve

 

 

References from Kyoto University Archives and Japanese Cruisers of World War 2 by Eric Lacroix and Linton Wells II

[Vladimir__Poutine]

Nice.

[anonym_s4TCbLNuhWyC]

A interesting Design... nice job :0 +1

[Crazy_Cossack]

I honestly don't read these. I just like looking at the pretty pictures.  :Smile_glasses:

[Jagdzeit]

looking at the picture... there appears to be a 5th turret between the forward 2... a very heavy broadside, methinks

[Daltron]

Jagdzeit, on 15 February 2013 - 04:39 AM, said:

looking at the picture... there appears to be a 5th turret between the forward 2... a very heavy broadside, methinks

Yeah... that's... that's the design.

Just like Mogami and Suzuya.

[wjmconfi]

Thanks，but I still want ask about the information about the Japan Paper CA Type A 1941,could you find some details about it?

[Azumazi]

wjmconfi, on 19 April 2013 - 12:06 PM, said:

Thanks，but I still want ask about the information about the Japan Paper CA Type A 1941,could you find some details about it?

Finding complete details about it is a bit hard. Quite a few of the Circle Five Program cruisers (Or the sixth, this part is in conflict) and designs are still in private archives and collectors. The data that is known, is that it was requested by the Naval General Staff in 1941 with a removal of limits of the Washington Treaty. They were to phase out their older Class A cruisers as they felt they were unable to meet the specified requirements they laid down. One of those major ones that was never able to be fulfilled was armored turrets. It actually proved to be a major weakness in their fights since they were easily knocked out by aircraft with bombs or rockets.

The only things that have been released to the public are the following.

Resistance to 500kg bombs on deck and turrets, resistance to 20cm rounds between 15000-25000m and resistance to 15cm shells in those same ranges down to 10000m and under the waterline. 35 knot speed, 3 float planes, and an armament of torpedo's (No number on amount listed). She was to be armed with 20cm guns same as the other Class A Cruisers.

Now here is where the conflicting data comes into effect.
Some claims that it was to be a 4 triple turret design, the issue with that is that they weren't any data to support that claim unless someone in a private archive has one with that design. In all reality she most likely would have been an enlarged Ibuki class ship with a longer hull and wider beam to hold more weight for armor and proper armored turrets, The extra hull size would also afford better AA protection with more guns. Those also are unknown. Many speculate 100mm AA guns but no amount or how they would be fitted.

An artist did an impression of the ship on shipbucket

http://www.shipbucke...Type A 1941.png

My only issues is that they never specify where they got their data on it from, and in many cases it could be just "Speculation".

Now a lot of people ask, how could you design a ship based on those numbers above? Easy actually, going off those requirements, many of those were the same for the Tone class in armor requirements excluding the turret portion. They have data on that so it wouldn't be hard to get numbers to resist those strikes. Much of the ship in my honest opinion would have been nothing more than an upgraded Ibuki in size, armament, with larger hull, better armored.

[anonym_s4TCbLNuhWyC]

A mighty fine looking ship :P interesting design overall :) +1

(i read more so i found more details and i found this design to be even more interesting :P)