Funny thing is, the American found out that a "Light" cruiser with 12 to 15 rapid fire 6 inch guns, can be absolute murder to other ships smaller than a battleship. That was one thing the Japanese lacked...rapid fire medium guns.
Of course they also found that you can do that with a "heavy" cruiser if you put enough weight and technology in the turrets and make a class of 8 inch gun cruisers that have three triple 8 inch rapid fire cannon turrets. See the Des Moines-class cruisers.
Funny thing is, the American found out that a "Light" cruiser with 12 to 15 rapid fire 6 inch guns, can be absolute murder to other ships smaller than a battleship. That was one thing the Japanese lacked...rapid fire medium guns.
Of course they also found that you can do that with a "heavy" cruiser if you put enough weight and technology in the turrets and make a class of 8 inch gun cruisers that have three triple 8 inch rapid fire cannon turrets. See the Des Moines-class cruisers.
As far as I know, the conversion from the 6.1 in/60 cal guns to the 8 in/50 cal guns did cause serious problems. This is what is stated from the Navweaps site (the first paragraph is about the Mogami class cruisers while the second paragraph is about the Tone class cruisers):
The original Naval General Staff requirements for the Mogami class as issued in 1930 called for the design to mount 15.5 cm guns in triple turrets but be able to have these replaced by 20 cm guns in twin turrets should the treaty be revoked or in case of emergency. However, the design of the triple 15.5 cm turret needed a larger roller race than the twin 20 cm mounting. As a result, when the Mogami cruisers were regunned in 1939/1940, their Modified E2 turrets needed a larger diameter roller path than the other E Models in order to fit the larger diameter roller path used for the 15.5 cm turrets. These turrets were also somewhat longer than the other Model E gunhouses in order to accommodate the larger roller path. As the 20 cm guns were longer than the 15.5 cm guns they replaced, the guns of No. 2 turret could not depress below +12 degrees when trained on the centerline as otherwise they would have struck No. 1 turret. These problems seem to indicate that little effort was expended during the initial design phase to meet the regunning requirement or that the designers were unable to come up with a solution that still met the very tight tonnage limits on this class.
The hull and barbettes of the Tone class had already been completed up above the armored deck when the main armament was changed from triple 15.5 cm turrets to twin 20 cm turrets. As described above (see Note 8), as the twin 20 cm turret needed a smaller diameter roller path than the triple 15.5 cm turret, this meant that the diameter of the completed portion of the barbettes was now too large to fit the standard turret races used for twin 20 cm turrets. To compensate, the design for the top of the barbettes was altered to a conical shape with a diameter of 18.7 feet (5.70 m) at the lower level and 16.4 feet (5.00 m) at the upper level. The follow-on Ibuki class were to use the same E3 turrets as the Tone class, but these later ships were designed from the start with 16.4 foot (5.00 m) diameter barbettes. However, the distance between the centerlines of No. 1 and No. 2 barbette on the Ibuki class was the same as for the Mogami class, which meant that the guns in No. 2 turret still needed to be raised in order to clear No. 1 turret.
Updated
Chikuma
2 ships in classMogami classTone classMikuma
Suzuya
Kumano
4 ships in classWhy am I a light cruiser?Well, because of (Washington) Treaty limitations...(Treaty)
Six heavy cruisers built as light cruisersTreaty -> Limited to 12 heavy cruisersLight cruiser155mm triple dual purpose gunLight cruiserThe treaty has been renounced. Quick, you two should change.After 1937...From now on I'm a heavy cruiser!Not my problem!Light Cruiser
-> Heavy CruiserBefore WWII:
(Japan) has 18 heavy cruisersLight cruiser
-> heavy cruiser