WWI Ended in 1917 when Germany forced Russia out of War and the Rest of the Allies sign a cease fire .
By 1920's the US pushes for the Washington Naval Treaty How would this treaty end up with Germany , A-H and the Ottoman Empires still around .
What would the German Fleet look like in the 1940's and how large would it be .
If there still would have been a sort of Washington Naval Treaty (which was very doubdtfull) the USA would not have participated in it, being a neutral, non combattant nation. Most likely her place would have been taken by Germany, who was not a looser by this scenario.
So even if the USA would eventually want to participate in the treaty, it would be playing the second violin, as she was not considered an equal of the traditional Great Powers, who would eventually be European, or, to a lesser sence, Japan. Simch the defeat of Russia by Japan in 1905, Japan was considered an equal to any European power, although still inferior to the West European ones (UK, France, Germany).
Since the economical and millitary situation in 1917 would have been different, opposed to the OTL, I can consider the participating States would formulate something like the following Naval power ballance:
UK = strongest
Germany = second
Japan = third
USA = forth
France & Italy = Fifth/sixth
In a ratio to capital ships only, (so far only Dreadnougth type battleships and battlecruisers) I can see a nummerical ballance of something like this:
5:4:3.25:2.5:1.75:1.75 (for: UK: Deutschland: Japan: USA: France: Italy)
I peace was to last for several years, the numerically strongest Navy, the Royal Navy would lead the numbers. If any reduction was agreed, mainly due to economical reasons and the competition between especially the USA and Japan in buildingprograms, the following seems reasonable:
Startingpoint 1921:
UK = 25 BB's/BC's (Five QE's, Five Royal Sovereigns, two Renown's, One Hood, Four Iron Duke's, one Tiger, three King George V's, four Orion's, last seven to be replaced by new construction of four G-3 Type and possibly a scaled down BB variant such as Nelson's.) All three light BC's of Glorious type to be rerbuilt as CV's
Germany = 20 BB's/BC's (Four Mackensen's, Four Bayern's, Five König's, Five Kaisar's, two Derfflinger's.) (Older BC's and BB's propably reduced to other functions, as with overcomplete British BB's.) (Special Allowance to reconstruct three Ersatz York Type BC's as CV's)
Japan = 16 BB's/BC's (Four Kongo's, Two Fuso's, Two Ise's, Two Nagato's, Two Kaga's, four Amagi's.) (Setsu reduced to other function) (Special allowance to reconstruct two building BC's as CV's and construct two additional BB's/BC's)
USA = 12 BB's/BC's (Proppably the newest only, already started to be completed.) (Two Collorado's, Two Tennessee's, Three New Mexico's, Two Pannsylvania's, Two Nevada's, One New York. Second New York and all 12 inch BB's reduced to other functions.) (Special Allowance for converting two Lexingtons to Aircraft Carriers as in OTL.)
France = 9 BB's (so far only four Courbet's and three Bretagne's. As stopgab Two Danton's retained.) Possibly Normandie canceled and replaced in mid twenties by new construction, replacing oldest BB's.
Italy = 9 BB's (Two Andrea Doria's, Two Conte di Cavour's, One Dante Alighieri, four Francesco Caracciolo Class.)
UK and Germany are allowed to built at least two, maximum seven (UK) and five (Deutschland) new ships with 16 inch guns, to counter the ones being built by USA and Japan. USA can replace USS New York/Texas by an additional 16 inch gunned ship.
Carriers are to be less considered, but appart from the reconstructionprogramm of surplus capital ships, the ballance in carriers is simmilar to the Capital Ship Ballance. The earliest Carriers, mainly smaller than 10,000 tons are not counted as active warships, but as experimental.
In numbers:
UK = 10 (Argus, Hermes and Eagle not counted)
Deutschland = 8
Japan = 7 (Hosho not counted)
USA = 5 (Langely not counted)
France = 3
Italy = 3
Cruisers are at first not limmited in numbers, but are in size and firepower. As in OTL the size is limmited to maximum 10,000 tons and 8 inch guns, according to the existin Hawkins Class of UK and building of IJN Furutaka class. Later the numbers were possibly to be restricted.
Destroyers are not limmited in numbers either, but in size, being a maximum of 1,825 tons and no guns bigger than 6 inch. (Some German DD's already shipped the 5.9 inch gun, as did some British ones.)
Submarines were allowed, given the situation, following the Armistrice.