The C, D, and E classes are presented as successive answers to changing cruiser requirements. The D class had considerable room for wartime improvement in principle. Time prevented the Royal Navy from carrying out those upgrades during World War II. The E class already incorporated part of the development that the older cruisers might otherwise have received.
Notable Point · 4:41-5:18
C, D, and E cruisers as successive design answers
The introduction places the E class in a design sequence after the C and D classes, arguing that the D ships had unrealized upgrade potential while the E ships already embodied part of the next development.