I will soon make a thread about the RN's 6+" cruiser designs starting from 1938 when I finish the last drawing. But there were quite a few I can tell. I think the growth of tonnage was more dedicated to ammo and mounting weight as well as ( I suspect) underwater protection as the last two designs (17.500 and 18.500tons) had the same armament and surface armour and almost the same hull size
Apologies for thread necro but have you had a chance to do this Tzoli?
With regards to the post(s) about the RN's Cruiser Forces circa 1939 and their plans, I don't know the source(s) you used but my own take on that is that the RN essentially viewed Cruisers as being for two roles/of two types rather than three:
(1) "Fleet Cruiser" role, screening against destroyers, surface recce etc for which smaller, handier designs were preferrable for the greater manouevrability (or "nimbleness").
(2) "Trade Cruiser" role, the RN liked to term this Trade Protection but it is essentially the same as Commerce Raider in terms of requirements! These were larger and designed for longer range and more isolated operations.
Thus the RN would view their forces circa 1939 as being:
Fleet Cruisers ("Legacy") -
C, D, E, and 5.25in re-armed
Hawkins and
Frobisher with the
C, D, and quite possibly even
E class ships being progressively rearmed for AA with 4in twin, 4.5in twin or similar; this re-armament might well mean that at any future conference the British would try to get them de-classified as cruisers and re-classified as something else!
Fleet Cruisers ("1930 on") -
Arethusa and
Dido types; I can see a lot more of these being wanted, especially or even to replace the
C/D/E types if they end up with sub-5in gun armament; I can also see a case of reuse where some
Dido hulls would be used as mounts for the 6in two-gun turrets used for secondary armament on
Nelson and
Rodney with three per ship so giving something like 4 ships closer to
Arethusa in type probably also mounting a load of 4in twins
Trade Cruisers ("Legacy") -
County class (13 ships),
York/Exeter (2 ships),
Leander class (8 ships and seen as a bit weak for the role),
Effingham reequipped with 6in guns.
Trade Cruisers ("Modern") - 10
Town class and the 9
Crown Colony class ordered in 1937 and 1938 or so
The RN broadly had opted for 6in over 8in from about 1930 onwards as they reckoned the ranges cruisers would be fighting at would almost all be in the envelope covered by both types but the number and rate of fire offered by the 6in was preferrable to the individual shell damage offered by the 8in while the majority of ships being shot at would be as unhappy with a 6in hit as an 8in hit; the USN had a different opinion but they did not give their cruisers torpedoes so might like having 8in guns to punch through battleship armour at close range (see Naval Battles off Guadalcanal!). The RN would also need to get a completely new 8in gun developed which would take time so for now I would see them ordering 6in armed cruisers.
Thus my (preferred!) thought is that the RN is going to order either more 3rd generation
Town class (
Edinburgh/Belfast) or a 4th generation as the capabilities offered on an approximately 10000 ton standard displacement is better than that offered by the 8000 ton hull. The orders for these would not only continue while the Royal Navies aimed for lots of these to keep trade lanes open but might also seek to replace the
Leander class,
Effingham, and possibly even
York/Exeter although by the time they are getting into the numbers to be doing this, there is a chance that a modern 8in gun and mount would have been prepared and could be swapped into some of these.
The
County class had been cycling through some impressive refits from the mid 1930s although war intervened after the first of the second generation entered the shipyards for this (
London) stopping the process. While
London's refit was shown up as weakening the structure etc when she was used in the very harsh waters of the North Sea/North Atlantic/Arctic the class were more suited for distant stations in the Indian and Pacific Oceans where she might have survived a bit longer or better!