I've been thinking about trying a 1920 start next, and I was wondering what size led to the most realistic legacy fleets. For 1900, it pretty much seems to me that very large is necessary to end up with fleets with numbers of dreadnaughts comparable to those in 1914. However, the 1920 starts that I've tried out seem to be a bit, well, large. And not well balanced either. Both times I looked at GB (on large and very large) there were enormous numbers of ships with 12" guns, and very few with anything larger. (Mostly 15").
Large probably works out best if you want approximately the WNT-mandated numbers and aggregate tonnage at game start; Very Large probably works out best if you assume that the ships scrapped in the early 1920s - whether in compliance with the WNT or before - are still in service at game start and the various powers have the rest of the 1920s to cut the fleet down to the treaty limits. Note that the computer fairly consistently scraps ships at ~20 years in service, so most of the old predreadnought and semidreadnought battleships in the 1920 legacy fleet will probably be gone by 1925 and the older dreadnoughts will likely follow c.1930.
As to the prevalence of ships armed with 12" guns, my feeling is that the fleet generator typically leans a bit too heavily towards the lighter calibers, but the legacy fleet generation can give fairly decent distributions of calibers in service. For example:
Other than the nine American and eight British pre-/semi-dreadnought battleships, which I consider irrelevant, these are the battle fleets of the various powers at the start of a 1920 France game that I recently began. If I haven't overlooked anything or miscounted, that's two 15", nine 14", six 13", two 12", and six 11" dreadnought/superdreadnought battleships and battlecruisers for the US (plus two 16" battlecruisers under construction); ten 15", four 14", seventeen 12", and four 11" dreadnought/superdreadnought battleships and battlecruisers for Britain (plus a 15" battleship and a 16" battlecruiser under construction); four 15", two 14", two 13", four 12", and seven 11" dreadnought/superdreadnought battleships and battlecruisers for Japan (plus a 12" battlecruiser under construction); thirteen 12" dreadnought/superdreadnought battleships and battlecruisers for Italy (plus a 16" battlecruiser under construction); and nine 13", ten 12", and four 11" dreadnought/superdreadnought battleships and battlecruisers for France (plus two 16" battleships under construction). Overall, a fairly reasonable distribution of calibers across the fleets of each power, though the dates in service are a bit odd and the choice of a 12" battlecruiser for Japan's new construction is a bit suspect.
Historically 15in weren't the norm for ships allowed to be retained under the WNT either. Large is usually my go to size for RTW, while very large allows for Jutland scale scenario, it does also bloat the size of other nations navy a bit, and is not super suitable for a post WNT world either. (Unless we can get AI to make proper ratio of escort/Cruiser to BB/BC/CV/CVL)
Historically 15in weren't the norm for ships allowed to be retained under the WNT either.
Not across all powers, true. On the other hand, for Britain specifically they were - 13 of the 22 ships Britain was allowed to retain until the completion of Nelson and Rodney were armed with 15" guns while the other nine were armed with 13.5" guns; once Nelson and Rodney completed, four of the ships armed with 13.5" guns were to be scrapped.
As to the other powers:
- Japan: Of ten ships, eight were armed with 356mm (14") and two with 410mm (16.1") guns.
- Italy: Of ten ships, ten were armed with 305mm (12") guns.
- France: Of ten ships, seven were armed with 305mm (12") and three with 340mm (13.4") guns.
- USA: Of eighteen ships, six were armed with 12", eleven with 14", and one with 16" guns; upon completion of two additional ships armed with 16" guns, the two smallest (and oldest) ships armed with 12" guns were to be scrapped, for four ships armed with 12", eleven with 14", and three with 16" guns.
Across all the powers, that'd be 23 (21) ships armed with 12", 12 (8) with 13.5", 19 with 14", 13 with 15", and 3 (7) with 16" guns. (Numbers in parenthesis are numbers after ships under construction are completed and older ships scrapped accordingly.) It should also be mentioned that of the 23 (21) ships armed with 12" guns, seven (three French and four Italian) were semidreadnought battleships, so if you're only counting dreadnought/superdreadnought battleships and battlecruisers it'd only be 16 (14) ships armed with 12" guns, of which only 6 (4) belonged to any of the top three powers (more specifically, to the USA).
I personally don't mind a bit of variation from historical numbers, but it's certainly a bit weird to see as great a preponderance of ships armed with 12" guns as is somewhat frequently the case in the 1920 start's legacy fleets even for the top three.