Gun availability favored 4-inch escort armament

Would a 3-inch/50-calibre gun have been a good main battery for Flower-class corvettes and later River-class frigates?

It could have worked, but the Royal Navy had plentiful 4-inch guns, so there was little reason to substitute the 3-inch/50.

A 3-inch/50-calibre gun could have served as the main battery of Flower-class corvettes and later River-class frigates. British escorts received 4-inch guns instead. The Royal Navy already had large numbers of the larger weapon available. Wartime armament fits often follow supply and procurement realities as much as an ideal paper specification.