Thanks everyone! As Hood says the primary threat facing this destroyer class is air attack during their time of service so the lack of an aft turret is less of an issue, but the follow-on class of destroyers will once more have a 4.5" mount aft.
The 2-pdr and 40mm combination is kind of an oversight by me, but I figure as this is the lead ship of the class commissioned during the war the 40mm mounts could be in short supply...
@BCRenown - thanks for the images, you've given me some ideas for the follow-on class