This class of cruiser was designed for use as Anti Aircraft cruisers in the fleet role, in response to demands for better Anti Aircraft defence against the growing capabilities of the aircraft of the day. The special Dual Purpose main armament was designed in the 1930`s and fired an 80 pound projectile and had a maximum range at full elevation of 70 degrees of 46,500 feet. It was mounted in twin turrets. Three of the turrets were in tiers forward of the bridge, which necessitated a high bridge and even higher funnels to prevent smoke problems on the command positions.

Scylla and Charybdis had 8 4.5" AA guns in four twin mounts instead of the designed 5.25" guns duo to shortages.