| BL 4.7-inch (120 mm), 45-calibre naval gun | |
| Type: | Naval gun |
| Is Ranged: | yes |
| Is Artillery: | yes |
| Is Uk: | yes |
| Service: | 1919–1948 |
| Used By: | United Kingdom |
| Wars: | World War II |
| Design Date: | Mk I: 1918 Mk II: 1940[1] |
| Production Date: | Mk I: 1919 Mk II: 1940[2] |
| Number: | Mk I: 187 Mk II: 32[3] |
| Variants: | Mk I, Mk II[4] |
| Weight: | Mk I: 7000lb Mk II: 7028lb[5] |
| Part Length: | 5.4sigfig=3NaNsigfig=3 bore (45 calibres) |
| Cartridge: | 50lb[6] |
| Caliber: | 4.724inches |
| Rate: | 5-6 RPM[7] |
| Velocity: | 814m/s[8] |
| Max Range: | 14450m (47,410feet) at 30°[9] |
| Breech: | Welin breech block |
| Elevation: | -9.5° to +30°[10] |
| Traverse: | -120° to +120°[11] |
The BL 4.7-inch, 45-calibre gun (actually a metric 120 mm gun) was a British medium-velocity naval gun introduced in 1918 for destroyers, intended to counter a new generation of heavily armed destroyers that Germany was believed to be developing.
Mk I, of built-up wire-wound construction with 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). Some saw service in World War I, but most entered service after the war ended.
It was also mounted on :
Mk II was a monobloc-barrel (i.e. single-piece, typical of small-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 They were superseded on new destroyers from 1930 by the QF 4.7-inch Mk IX.