Obviously we have the benefit of hindsight and could say something like "build loads of carriers and corvettes to best the uboats" but, with the many roles of the royal navy taken into account, what changes could be made to the Royal Navy immediately post WNT to make it a better fighting force for its many tasks. I would include a slightly more conventional Nelson class, possibly with 15' guns and a bit more speed, along with trade protection carriers, maybe have the counties with three triple turrets ins yes do four twins and, although opening a can of worms here, not extending the battleship holiday with the LNT.
https://history.state.gov/milestones/1921-1936/naval-conferencehttps://history.state.gov/milestones/1921-1936/naval-conference
Hindsight but with the facts in hand that the Treaty regime was signed in 1922, effective in 1923, and in place until the end of 1936, and that Japan was the only likely major enemy for at least 10 years, but a European challenger would be likely after that point:
Capital ships:
1. Complete the two new-builds as balanced 35,000-ton designs, capable of 30 knots and with 3x3 15/42 main battery and 4.7 inch DP secondaries;
2. Plan on modernizing the three battlecruisers in the mid-1930s, with the
Queen Elizabeths to follow, if necessary;
3. Maintain all the existing 15/42 guns, turrets, etc., whether aboard the existing ships or stored;
4. Preserve and maintain all the existing 13.5 inch ordnance as the older ships are scrapped.
Aircraft carriers:
1. Convert the three light battlecruisers to a single standard design equivalent to
Glorious with a full-length flight deck, so perhaps 60 aircraft, divided between fighters and torpedo bombers;
2. Group the two new fast battleships, the three battlecruisers, and the three large carriers, as they complete, into a fast "scouting force" type organization with cruisers, destroyers, and replenishment ships to match and train and exercise along those lines;
3. Commission
Eagle and
Hermes (they're too far along not to) and assign them to serve as the carrier support for the battlefleet (
QE and
R types);
4. Buy enough aircraft to fill and sustain five operational air groups;
5. Keep
Argus as a training carrier and wartime trade protection;
6. Design work in peacetime for fleet and trade carriers; eyes on likely conversions.
Cruisers
1. Build the County class ships as large, long-range, well-protected ships, but with 3x3 6 inch main battery turrets and twin 4 inch DP secondaries;
2. Convert the
Effingham and
Emerald class ships with 3x2 6 inch main battery turrets;
3. Maintain the
Danae class ships as the backbone of the cruiser force to support the battlefleet;
4. Convert the Ceres class ships as AA cruisers with twin 4 inch DP turrets;
5. Don't build
Adventure; use the tonnage for conventional cruisers or sloops, if possible;
6. Design work in peacetime for large light cruisers (4x3 6 inch turrets, 12,000 tons).
Escorts:
1. Build the A-I, but with 3 DP 4.7 or 4 DP 4 inch, rather than SP;
2. Maintain all the late-war Leader and V&Ws possible;
3. Build all the large sloops possible under the Treaty limit of 2,000 tons, with 4.7 or 4 inch DP main batteries;
4. Prepare small sloop and coastal minesweeper/escort designs, but don't build them in peacetime, other than for yard needs and limited training duties;
5. Design work in peacetime for fleet destroyers and sloops (large and small).
Submarines:
1. Prepare a series of small "coastal" designs for inshore and the Med, and "large" ocean-going designs for the Pacific;
2. Build a small number of each to keep the yards going, but limit the numbers to reduce peacetime costs;
Transports, amphibious forces, and landing craft:
1. Build enough to sustain and land two infantry brigade groups in peacetime;
2. Prepare designs for series production in wartime;
3. Sustain two mixed brigade groups, RMs and army, in the UK, and train them for opposed landings using the ships above; deploy RM battalion combat teams to the Med and Pacific in peacetime for training;
4. Work with the aviation services toward a CAS doctrine.
Auxiliaries:
1. Build or convert the basic types for a fast replenishment force and fleet train for the Pacific;
2. Design, train, and study trade conversions, emergency merchant shipbuilding plans, naval control of the merchant fleet, convoy and routing, mine warfare, and harbor defense for wartime needs;
Aviation:
1. Beg, borrow, or steal the equivalent of the RNAS back from the RAF, and equip whatever units they can get with modern aircraft capable of operating from realistically extemporized bases in Pacific theater conditions.
2. Plan for war.
Allies:
1. Build up the Commonwealth navies as much as is possible under the Treaty regime and with realistic budgets, with as much standardization, exchanges, and training as possible;
2. Do as much as is diplomatically realistic with the US, French, Dutch, Greeks, Portuguese, South Americans, Italians (if possible), etc.
In a lot of ways, it's an RN that looks more like the USN during the interwar period, but since the IJN is the only likely enemy for at least 10-15 years, that makes sense; by the mid-to-late 1930s, focus will shift back to European waters, but the legacy "Pacific" force should be large enough to have some positive impact on Japanese strategic thinking, even in the 1940s, and the "Pacific War" training and capabilities will all be useful in the Med or eastern Atlantic.
Otherwise, the RN will face a three-ocean war with a 2-ocean navy designed for Europe - as it did, historically.