With the Yamato class being in their final years of building, new large ship construction could be contemplated. The priority was aircraft carriers, then cruiser escorts. These ships would not need to be as big as the preceding Takao class which had been designed to destroy the 'Treaty' cruisers built by other 'enemy' nations. Having gone to a triple turret aboard the Takao I can now stick with triples for the next Mogami class. This dramatically shortens the overall length of the hull by approximately 60 feet. Deepen the lower hull and freeboard, widen the hull for fitting the triple turret, and you have a hull that will not make 36 knots, more like 32 or 33. In my Japanese Navy that is all that is required and the hull stability is far superior to its real life namesake. War time additions centered on more and more 25mm AA guns and radar on those ships that make it that far.
I have always been intrigued by the Japanese Navies obsession with speed. In real life these ships made 35-36 knots. But like most of their peers they were inherently unstable. To add anything to the ships required bulges being fitted, which reduced the speed of the ships anyway. Speed gives two options. One, approach your enemy very fast, or two, run away from your enemy very fast. I can not see why the Japanese would need either. For use as destroyer leaders? Does not wash either. The smaller the ship the slower they go in moderate to rough seas. A destroyer with a speed of 36-39 knots in a flat calm may only make 30-32 knots in moderate to rough seas. Cruisers being much bigger are able to sustain better speeds in moderate to rough seas, where destroyers would have trouble keeping up with them. Having the Long Lance torpedoes, the Japanese did not have to rush their ships into torpedo range under large amounts of gun fire. Their Long Lance torpedoes fired further than the cruisers and destroyers guns. High speed for running away goes against all things Japanese, so I never considered that as a reason.
Twins versus triples. A twin turret should fire faster than a triple turret. The interference in loading guns is what makes the difference between the twins and triple. Less working space around the guns in a triple turret. The only instance I can think of where the triple turret would work as well as a twin is the German triple 11", the gun housing is huge for the size of the guns. Very little interference. The worst I can think of is the early US triple turrets on the Pensacola ten 8" gunned ships. The space between the guns in those triple turrets is minimal.
This class takes the Japanese cruisers up to the outbreak of war. War built ships will concentrate on smaller 6.1" cruisers with triple turrets in nine and twelve gunned ships, and the hybrid Akizuki type AA cruiser/destroyers.
