Krakatoa said " Once the 4.5" DP gun is available the destroyers armed with those become much more useful."
I assume you meant the single mount?
The 4.5in Mk V fitted in the Z and C classes was (apart from the barrel and its fittings) identical to the 4.7in Mk XXII fitted in the T to W classes; handworked, upper elevation limit 55 degrees, so better than the 4.7in Mk XVIII, but still hardly a genuine DP weapon.