The shift towards smaller cruisers in the late 1930s was driven mainly by the 1936 London Naval Treaty. The 'Town's were built under the regime of the 1930 London Treaty, which placed a maximum cruiser tonnage of 10,000 tons. The 1936 treaty lowered this limit to 8,000 tons for ships laid down after 31st December 1936. The 'Crown Colony's were, in essence, a scaling down of the 'Town's to meet this new limit; retaining the same armament and many of the same capabilities on a slightly smaller hull with less armour. Doing so meant many unsatisfactory compromises. Most 'Crown Colony's completed slightly overweight, making it harder to add extra anti-aircraft guns, radars and fire control equipment without removing extra topweight. They were also considerably more cramped than previous cruisers. The mess decks were more luxurious than previous ships - the 'Crown Colony's were the first ships to carry a laundry and to have hot and cold running water in the basins - but they were heavily overcrowded. They had a design complement of 710, but over the course of the war, this would rise to over 900. They did have several small advantages over the 'Town's. They used the same 'long stalk' 6in turrets as the two Edinburghs, which needed a smaller crew and were more reliable. The magazines for the 4in secondary armament were placed directly under the guns, reducing the number of crew eneded to work them. They had a flat transom stern, which was more hydrodynamically efficient. This made the 'Crown Colony's slightly faster and slightly more fuel efficient.

In May 1940, work on three 'Crown Colony's was suspended during the invasion crisis. They were completed to a slightly modified design, incorporating the lessons of the early war, becoming known as the Uganda class. The most drastic change was the loss of X turret. This was exchanged for extra anti-aircraft weaponry - at first two twin 4in dual-purpose mounts, but this was eventually reduced to a single quadruple mount for the 2pdr pom-pom, which was viewed as a more effective AA weapon. Most of the 'Town's and 'Crown Colony's would also have X turret removed and replaced with increased AA firepower, but this was an impromptu modification rather than being made in the design stage (Belfast was the only one to avoid this, having had buoyancy-increasing blisters added to strengthen the hull following serious mine damage in 1939). Another important change was the removal of the catapult and hangars for the seaplane - these had been found to have only limited utility and took up a lot of space. The hangars were converted into accommodation spaces, plus a cinema or chapel. Similar modifications would also be made to the older cruisers, but this was again an impromptu change. The accommodation spaces were better arranged, reducing the distance men had to travel to reach their action stations. The electrical system was set up to be immediately compatible with radar systems, unlike earlier cruisers. The bridges were heavily redesigned; an admiral's bridge was added below the main compass platform, weather protection was increased and views of the sky were improved. A Fighter Direction Office was added, allowing these ships to use their radars to direct combat air patrols.

The next class, the Minotaurs or Swiftsures, were a further development of the Ugandas. Ordered in late 1941, they added an extra foot of beam onto the base 'Crown Colony' design. In general, they retained many of the features of the Ugandas; they had only three 6in turrets, and no aviation facilities. The forecastle was extended back to close off the area that the catapult originally occupied, increasing space for accommodation. They had a considerably heavier AA armament than their predecessors, mounting five twin 4in turrets, four quadruple 'pom-pom's, another four pom-poms on powered single mounts, and twelve twin 20mm Oerlikon guns. They also had added fuel capacity, increasing the range by ~400 nm. In 1942, a further set of improved 'Crown Colony's was ordered; only one of these would be completed. Superb added a further foot of beam to the Swiftsures. She had further increases to her close-in AA armament, completing with four quadruple and two single pom-poms, eight single mounts for the 40mm Bofors gun, and ten Oerlikon guns (four twin mounts plus two singles). She was equipped with new model fire control directors capable of blind-fire, though the new fire control computers intended for them were delayed, and would not see service during the war.

The final class of cruisers ordered for the RN during the war were the three ships of the Tiger class. As originally conceived, these would have been similar to Superb (she had been ordered as the first of the new class). None were completed before the end of the war, and the designs were updated. The main change would have been new mounts for the 6in guns; the Mark XXIV mount, which could be controlled directly by the fire-control directors. There were also improvements to the infrastructure of the ships. An automatic telephone exchange, and a 'ring main' electrical and pump system were to be fitted. Some aft bulkheads were made more solid, and counter-flooding systems improved. These changes were heavily delayed due to a lack of skilled draughtsmen and the prioritisation of work on new carriers; by the time work restarted, priorities had changed. They would instead complete with two twin 6in turrets. These Mark XXVI mounts had an autoloader, allowing the guns to fire fully automatic at a rate of up to 20 rounds per minute. The secondary armament was three 3in mounts, again autoloading fully automatic weapons (with an astonishing fire rate of 90 rounds per minute). Two of the ships would later lose their after 6in mount, which would be replaced with a hangar and flight deck for Sea King helicopters.

It should also be noted that there were many changes to the equipment and armament of the RN's cruisers over the course of WWII. As noted above, by 1945, every 'Town' or 'Crown Colony' bar Belfast would have lost X turret, in return for an increased radar and AA armament fit. There was a considerable degree of convergent evolution, with similar changes made to both classes. All classes found themselves carrying out similar roles in combat, with general success.