BL 4.7-inch 45-calibre naval gun

It was designed to counter a new generation of heavily armed German destroyers that were believed to be in development.

Mk I, of built-up wire-wound construction with a propellant charge in a cloth bag, went into service beginning in 1918 on destroyers of the new Admiralty type destroyer leader (Scott class) and Thornycroft type leader (Shakespeare class).

It was also mounted on : Mk II was a monobloc-barrel (i.e. single-piece, typical of small to medium World War II guns) gun of similar performance introduced in World War II to replace the worn-out Mk I guns on surviving ships.

These were the only BL-type 4.7-inch guns in British service; all others have been of the QF-type.

They were superseded on new destroyers from 1930 by the QF 4.7-inch Mk IX.

Gunners on destroyer HMS Broke , September 1940
On a Landing Craft Gun (L) , preparing for the Invasion of Normandy, 1944