ORIGINAL: HMS Resolution
With the extra two 8-inch cruisers, will the British be building Surrey and Northumberland from the 1928 programme?
I've played around with different outcomes to the Washington Treaty myself, and it seems to me that, with more of the budget going to new battleships, the first effect would have been a slower buildup of the cruiser force, because there was no urgent need to modernize the older BB's yet, and the CA program was the biggest budget item after the new BB's post-WT. Either fewer ships in the Kent class, with the London class and later ships more stretched out, or maybe smaller ships like Exeter/York, maybe even ships armed with 7.5 in guns.
As to the new BB's: would the RN have stayed with 15", when the main rivals went for 16" in a big style? This was a matter of prestige and not to be taken lightly; the KGV's were massively vilified for having a smaller caliber than anyone else. The G.3 design could have been squeezed down to 41000 tons, by accepting slightly lesser armor thicknesses and other mods. The Nelson class came out 1500 tons underweight, so there would have been some leeway for the G.3 (mod). And they would still have been faster than most other ships. The J3 design seems hardly better protected than Hood, especially in regard to the deck; I don't think the RN would have gone for another "egg shell armed with sledge hammers" design for their new super ships.
Another wrinkle concerns the Hood. After Jutland, the classical battle cruiser concept was in the dog house. Hood only survived because the Admiralty knew Germany was building enlarged Mackensen class BC's with 15" guns. Hood's planned sisters were at first suspended and finally cancelled when it became clear Germany wouldn't be able to complete any of its new BC's. The Director of Naval Construction (I think it was still Sir Philip Watts) wanted to scrap Hood on the stocks to make way for something more worthwhile. I think he might have gotten his way if the Admiralty had realized a bit earlier what was happening to the German building program. Now what kind of clean-sheet design would the RN have come up with in 1917?
Concerning Japan: in 1922, nobody was certain about how carrier aviation would work out, so I think Japan would hardly have built dedicated carrier escorts at the time. They were still concentrating on the Decisive Battle, so I think they would have gone for a modified Nagato design with the max allowed displacement (and might have cheated about that) and used the rest of their allotment for some experimental design several years later.
As to cruisers: more Myoko/Takao class ships. Alternatively, the Mogami class might have been designed as 10K, 8" ships from the start, which would have put paid to the 155 mm guns. As to why the 155 mm wasn't used on the Agano class:
comparison of 140/150/155 mm guns
shell weight 38/45/56 kg (84/100/123 lbs)
barrel life 500-600/500-600/250-300 rounds
The CLs switched to 140 mm guns because it was felt that the 150 mm shells were too heavy for Japanese loaders in a prolonged fight. I think that they would have gone for a new design 140 mm gun for the Aganos if they could have freely chosen, using the 150 mm Vickers design was just for expediency. A design like Oyodo, but with a third 6" turret aft, sounds good, too, but I've always had a weakness for the French La Galissonnière class with a similar layout.
