This class was based very much on the erlier vessels, but carried a heavier and more varied armament : the RN first group carried 4.7" LA guns and not the earlier 4" AA guns; controlled by a pedastal director on the bridge. The bridge was also moved farther back, to allow a shelter deck and 12pdr AA to be fitted, and a quad MG completed the armament, stuck behind the funnel.
Aberdeen carried the different armament of 4 inch guns in all positions plus on the quarterdeck and retained the machine guns, but only ever shipped two of these guns until early war, when the third was shipped on the shelter deck.
Fleetwood, however, was building when the new twin 4" AA mount evolved, and as this was obviously far more suitable for an escort, it was carried in "A" and "X" positions, "Y" gun was omitted and a second 0.5" mounting was placed on the quarterdeck - and a rudimentary HA control system was fitted, a rangefinder and a fuse setting clock. Grimsby and Deptford were similarly re-armed pre-war.
The war modifications were to first remove the mainmast, and add a second ( or third ) multiple 0.5" MG, later to add two single 20mm AA in the wings. SW type 271 was fitted in ships with 4.7" LA guns, and a HA.DCT with AR type 285 was fitted to those ships with 4" AA guns, and all ships carried AW type 286 or 291 at their masthead. Later, the multiple machine guns were replaced by two 20mm cannon in most ships, and a hedgehog was mounted on the shelterdeck, replacing either the 4", 12pdr or 0.5" gun.