Chuck wrote:
That is undoubtedly attributable to the lack of industrial capacity or inadequate priority to produce enough new 6" barrels. The Japanese already has developed a superlative native 6"/60 gun, generally acknowledged to be the best 6" naval gun of WWII period, for the Mogami class. Guns of that design would seem to be easily the most obvious choice for the new CL had Japanese been able to deliver enough of them in time.
Which is interesting, because the 15.5cm mounts you refer to became surplus in precisely the time frame these ships were designed.
Who, by the way, besides a small number of Japanese officers would be able to evaluate or compare them with the properties of other 15cm guns? A gun, powder, and shell is a complex and dynamic combination. A few calculations on the back of an envelope are insufficient to qualify them in any way.
It appears there were 112 fully assembled guns and spares, only 30 of which were further employed aboard ships after rearmament; 24 were destined to swing uselessly at anchor for most of the war as secondary armament on the
Yamato and
Musashi.
The four
Mogamis alone provided 20 surplus turrets. Eight more were in various states of construction when the order changed
Tone & Chikuma from Class "B" to Class "A".
This strongly implies that the Japanese found some cardinal defect either in the gun or it's fire control system, and chose the Vickers 6-inch instead for these cruisers.
My suspicion is that these guns suffered from excessive barrel wear and projectile hammering, with a 3000 f/s muzzle velocity and 6 caliber head radius (a long) shell. It is also possible that these very long shells either tumbled in flight, or suffered severe dispersion. The USN had the latter problems for some time with the 8-inch/55 caliber guns until the shell head radius was modified and the muzzle velocity brought down.
In any event, the Japanese 15.5cm/60 only went to war on one cruiser, the "headquarters ship"
Oyodo (besides the two
Yamatos), and she at least never fired them in anger.