The E class were based on the preceding Danae class, but had a very high ratio of length to beam, and only one more gun despite being much bigger and more expensive. Much was sacrificed to achieve 33 knots (61 km/h), the horsepower was doubled and the hull increased by 100 ft (30 m) in length, and a 50% increase in displacement. Only two ships were actually built, and completed in 1926. Four propellers were necessary for the increased power, and were driven from two engine rooms. There were four boiler rooms, nos. 2 and 3 being arranged side-by-side with the exhausts trunked into a common funnel. The magazines were between boiler rooms nos. 2 and 3 and the forward engine room, and between boiler room no. 4 and the after engine room. This led to a bizarre funnel arrangement, accentuated further when in 1935 a longer catapult required the mainmast to be stepped forward of the after funnel, and the funnels were heightened by 5 ft (1.5 m).

In the early 1930s Enterprise was fitted with a prototype twin 6" turret in place of her two forward single mounts; and with trials of the turret proving successful it was retained on Enterprise until rebuilt 1935-37. The turret design was later installed in the Leander, Amphion and Arethusa classes. The turret installation occupied less space than the superimposed 'A' and 'B' guns of Emerald, therefore the bridge was placed further forward. The bridge was of a new design, being a single block topped by a director tower, rather than the traditional platforms built around the foremast and wheelhouse topped with a spotting top. (Taken from Wikipedia) This design of bridge would appear in many cruiser classes in the future.

With the rebuilding of the ships and the resiting of the 6" magazines a more normal appearance could be acchieved, these two ships were still the fastest cruisers in the Royal Navy at the outbreak of World War II, Emerald exceeding 33 knots (59 km/h) in a full-power trial at full load in 1939.