Norman Friedman says in "Modern Warship", that this configuration was chosen for length
reason, as the missiles were stowed in tandem rows and not parallel in the County class.
Perhaps the text gives a better description :
"Unlike Terrier and Talos, the British Seaslug employed a booster wrappe around
the missile propoer - in effect it traded length for diameter. Instead of a ring of
missile bodies, Seaslug stowage is a string of assembled missiles, eac on its own
trolley, leading up to the launcher rail.Ship-impact was tremendous: much of the
superstructure deck of a 'County' class missile destroyer conceals the Seaslug ready-
service stowage, one line of missiles for each side of the launcher. Other missiles, not
assembled, are held in a magazine."