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The Mogami Variants

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Alpha Tester
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357 battles

As the title says:




These variants are:

- Mogami class light cruisers as designed and laid down.
- Mogami class light cruisers (IJN Mogami and Mikuma) as finished
- Mogami class heavy cruisers (IJN Mogami and Mikuma) as refitted
- Mogami class heavy cruiser IJN Suzuya as proposed for anti aircraft heavy cruiser conversion
- Mogami class heavy cruiser IJN Kumano as proposed for anti aircraft cruiser conversion
- Mogami class heavy cruiser IJN Mogami as rebuilt to aviation cruiser
- Mogami class heavy cruisers as proposed to be rebuilt into light aircraft carriers

Note how the aircrafts which was carried changed over time.

More detailed info on the variants:

First variant:
After the sign of the First London Naval Treaty of 1930 Japan reached it's maximum allowed heavy cruiser tonnage by the completion of the 4 units of the Takao class and thus it had to cancel the following improved Takao class heavy cruisers. The tonnage limit for light cruisers too were very close to the set limit but by scrapping 4 pre-WW1 era protected crusiers of the Tone and Chikuma classes (3 ships), and replacement of the Tenryu class (2 ships) and the Kuma class (5 ships) by 1934 and 1937 allowed Japan to build 6 new light cruisers which then became the Mogami and Tone classes.
Originally the Mogami class would displace only 8500tons standard but the requirements of the navy was so similar that of the 10.000ton Takaos that standard displacement risen to 9500tons and different weight saving measures had to be taken to reach this goal and thus Design C-37 was born.
As the drawing illustrates the Mogami class as born was quite different from the ones actually finished. A bridge very similar to the Takao was adopted despite it's large mass resulting top heavy problems, large surface area for enemy fire and wind resistance counterweighted the positive points of centralised placements of fire-control, communications and navigational stations, the quadrupedal foremast was also taken from the Takao class. By reducing the boilers from 12 to 10 a single funnel could be adopted as well. A protected hanger was provided for the seaplanes which was almost identical to that of use on the Takaos. Main armament was chosen to be 15x 155mm guns in 5 triple turrets from the very beginning and because they are designed to provide AA fire, the secondary armament was chosen to be only 4 single guns but of new type (12,7cm Type 89). Torpedo armament and placement too was very similarly arranged that of the Takaos.

Second variant:
This is how Mogami and Mikuma was commissioned. After the Tomozoru incident of 14th of March, 1934 plans were created to fix the stability issues of the Mogami class (among other ships of the fleet as well). These plans (unofficially known as the first efficiency or stability improvement works) were completed in June of that year but the first two units were already launched while he other two just laid down. The plan included the strengthening of the transverse bulkheads, replacing the large Takao style bridge with a much smaller one cutting it's weight by 2/3rds, removal of the seaplane hanger and rework of the aft superstructure, reducing their weight by half. Various deck height reductions were included, as well as moving the torpedo tubes further aft, increase the AA guns to 4 twin from 4 single mounts, and reducing the number of boilers from 10 to 8 in the last two units: IJN Suzuya and IJN Kumano.

Third variant:
In 1937, following the denunciation of the 2nd London Naval Treaty of 1936 in the IJN decided to construct new ships and continue to modernize or refit the existing units, including the battlecruiser Hiei and light cruisers of the Mogami and Tone classes. While the barbette diameter of the Tone class was changed during construction there were no problems for them to fit the 20cm twin gun turrets used on the other cruisers but Mogamis was already finished by this time so construction new turrets postponed their refit. This refit (unofficially known as the third efficiency improvement or main gun replacement works) included the change of the 15,5cm triple turret to the 20cm twin ones, replacing the older Type 90 torpedoes with the newer Type 93 ones also known as Long Lances, replacing the seaplane catapult with a heavier and stronger one as well as torpedo-firing command station on top of the mainmast.

Fourth variant:
After the battle of Midway in which Mikuma sunk and Mogami was heavily damaged only 3 operational Mogami class cruisers remained in service. Between late 1942 and early 1943, while Mogami was underwent repair and conversion into an aviation cruiser to increase the fleet's scouting capability, plans were drawn up to convert both Suzuya and Kumano into Anti-aircraft cruisers. The plans included the replacement of all the main 20cm twin turrets to twin 12,7cm DP-AA mounts as well as increase of light AA gun armament. Though original plans included to convert both of the two fully operational cruisers to Anti-aircraft ships, most likely to wartime shortage of 12,7cm guns as well as suitable dockyard capacity, Suzuya would only got her aft guns replaced by the mentioned AA weaponry while still able to provide the same firepower as the Furutaka and Aoba classes.
Sidenote: I've taken the liberty to add more MG director towers knowing the ship's changed purpose to AA instead of surface combat.

Fifth variant:
While IJN Suzuya would only got half the AA gun replacement that was proposed, IJN Kumano could had received the full conversion creating a potent AA platform rivalling even that of the USN's Atlanta class Anti-aircraft light cruisers. Other changes likely would be included the replacement of the main gun rangefinder with High-angle one as well as more Machine-gun director towers for controlled AA fire.

Sixth variant:
After the battle of Midway Mogami was heavily damaged and between late 1942 and early 1943, she underwent repair and conversion into an aviation cruiser to increase the fleet's scouting capability. This time the entire aft section of the ship rebuilt removing the both turrets (one was heavily damaged) and their ammo storage rooms was modified to hold gasoline, bombs and other ammunition. The aircraft deck extended to the stern with a rail system to move the designed complement of 11 Aichi E16A Zuiun floatplanes though at first she carried a mix of Mitsubishi F1M Pete and Aichi E13A Jake floatplanes. Her light AA armament also increased with associated directors as well. After the conversion was finished her main role as frontline combatant changed to a more supportive role to provide reconnaissance and scouting for the fleet with the ability to launch all her planes in roughly half an hour.

Seventh variant:
Shortly after the battle of Midway at the end of June 1942 proposals were made to quickly replace the carrier losses of this devastating battle. As no new fleet aircraft carrier to be excepted operational at least until 1944, conversion plans were made for all the cruisers and battleships of the Imperial Japanese Navy. Soon the Furutakas and Aobas were ruled out as considered too small and the Yamatos were not just new but too important for conversion. 
The conversion of the battleships (4 Kongo, 2 Ise, Fuso and Nagato) would take 18 months and would result in vessels with around 210-220m x 34m flight deck and an aircraft capacity of roughly 54 planes. In the end the Kongos were ruled out because with their high speed they could escort the carriers, while the Nagato's 410mm cannons were still considered a powerful armament, this lead to the decision of the Fuso and Ise classes with Hyuga's aft turret damaged this made the decision straight: Ise, Hyuga followed by Fuso and Yamashiro.
As for the cruisers (4 Myoko, 4 Takao, 3 Mogami and 2 Tone), the conversions would took around 8 months to finish and would result in light carriers with 195-200m x 23,5m flight deck and an aircraft capacity of roughly 30 planes. In the end only the partially completed Ibuki was chosen to be finished as such a carrier, but even her was not finished in time.
My drawing represent the Mogami class conversion into CVL, though I do not have any drawings of the plans I do have access to the Tone's similar conversion and the Ibuki from which I've created this.

For those who are interested in the Tone class (IJN Chikuma to be precise) original sketch drawing showing her converted form, you can find it here:


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