Why Tribals did not simply receive 4.5-inch dual-purpose guns

Why were Tribal-class destroyers not simply fitted with 4.5-inch dual-purpose guns?

The suitable destroyer-scale dual-purpose mounting was not yet mature, while the available capital-ship-style mount was difficult to integrate into the class.

Fitting 4.5-inch dual-purpose guns would have improved the Tribal-class destroyers, especially in air defence. The obstacle was not simply gun weight but the state of the mounting: the suitable destroyer-scale design was still being worked out and had persistent problems. The Royal Navy therefore used a capital-ship-style dual-purpose mount rather than the more compact design that would have fitted these destroyers more readily. A desirable weapon cannot be treated as available until its mounting and integration are mature.