British 4.7-inch gun anti-aircraft limits

Why was the British 4.7-inch gun a poor anti-aircraft weapon compared with the US 5-inch/38?

The British 4.7-inch was a low-angle weapon shaped by expectations about level bombing and destroyer roles. Moving to 4.5 inches made a general-purpose mount easier.

The 4.7-inch gun's weakness came from its low-angle design assumptions. British planners expected destroyers to face different air threats and assumed heavier attacks would fall on capital ships. Later general-purpose needs made the 4.7-inch mount unwieldy. Moving to 4.5 inches eased space, balance, and handling problems inside the mount.