In World War II the gun was employed on many small warships such as Flower-class corvettes and minesweepers, primarily for action against surfaced submarines.

This was the last BL 4 inch gun in British service: all subsequent guns have used charges in metal cartridges "QF".
 It was succeeded on new small warships built in World War II by the QF 4-inch Mk XIX gun which fired a slightly heavier shell at much lower velocity and had a high-angle mounting which added anti-aircraft capability.
In World War II the gun was employed on many small warships such as Flower-class corvettes and minesweepers, primarily for action against surfaced submarines.
This was the last BL 4 inch gun in British service: all subsequent guns have used charges in metal cartridges "QF".  It was succeeded on new small warships built in World War II by the QF 4-inch Mk XIX gun which fired a slightly heavier shell at much lower velocity and had a high-angle mounting which added anti-aircraft capability.
BL 4-inch Mk IX naval gun