Why Royal Navy anti-aircraft standardisation lagged

Why did the Royal Navy enter the war without fully standardising its anti-aircraft armament?

Two earlier programmes failed at opposite extremes, and the practical 4.5-inch compromise was accepted only as war mobilization began. Existing stocks and the need to arm new ships then limited immediate conversion.

The Royal Navy did not simply ignore anti-aircraft standardisation. An early programme failed because it was not ambitious enough, while a later effort sought a single gun that would be an ideal answer to both aircraft and ships. The 4.5-inch weapon succeeded as a compromise rather than a perfect universal gun: it hit less hard than the 4.7-inch but reached well, and it fired less rapidly than the 4-inch while delivering a much heavier shell. The Navy took roughly fifteen years to accept that a seventy-five-to-eighty-percent solution to both missions was preferable to waiting for perfection. By the time the decision firmed around 1937, war preparation competed with the conversion programme. Existing guns and ammunition also remained useful, while new 4.5-inch production was urgently needed for new construction.