Actually, I'm pretty sure thats a misconception. Both designs were filed as B65, just different variants (Like all the Yamatos were A140).
As for how they compare, the B65 in my opinion is definately the better of the two ships;
While exact details on the protective scheme are sparse for the B65, the belt would have been of almost equal thickness and inclined at 20*, and likely better overall than Kongo's. The deck is generally quoted as 125mm, which is superior to what the Kongo's had, though there are no details if this is in a single deck or in layers. The former would make it vastly better than Kongos arrangement.
The ship is also likely to benefit from better subdivision than the older Kongos, though depending on when they get built, they may end up suffering from the declining quality of Japanese steel later in the war.
The twin turrets on Kongo weigh around 650tons, some sources put the B65 turrets at 1000tons. While this includes the extra weight to support the wider turret and extra gun, it also points to there likely being more armour on the turrets too compared to Kongo.
The 31cm/50 is an interesting weapon, firing something of a Japanese 'superheavy' shell at 1265lbs. This is even heavier than the shell on the USN 12in/50, and almost as heavy as Kongos shell. Like all superheavy shell guns, it suffers from a loss in range and short range penetration, but will likely be vastly superior as a deck penetrator at 20k+ yards. Ill run these through NAaB and FaceHard later, I think they included projected data for this gun. The guns also had a reasonably higher maximum ROF than Kongo, but its debateable if this is of any use at longer ranges, or if the shell handling arrangements could have kept pace with it. In a night action this may have helped.
Unlike the Kongos they have a large uniform secondary battery of 10cm/65s, which means an overall better AA defence and likely superior against light ships like DDs. Kongos arrangement is however probably better against CA/CLs, as the small shell from the 10cm isnt going to go through much armour, whereas the 15cm secondaries on the Kongo despite also being HE only, probably will.
No idea why they put torpedo tubes on the thing. Maybe cause its a cruiser.
At 34knots the B65 can keep up with all the CAs and CVs when needed, whereas the 30knot Kongos could not. The large machinery is going to be more expensive, at some 35,000 more SHP than Kongo it is even more powerful than that fitted in Shokaku, and this might be a real problem. Unless I'm off, it would be the most powerful set of engines in the entire IJN!
Apart from this, B65 would likely benefit from superior firecontrol than Kongo, both HA and LA, as she could be designed from the start to make use of all the advances instead of being modernized like the Kongos.
Thats about all I can think of for now...
< Message edited by JuanG -- 12/22/2009 11:02:32 AM >