BL 4-inch Mk IX naval gun
| Ordnance BL 4-inch Mk IX gun | |
|---|---|
On Flower-class corvette HMCS Calgary in World War II | |
| Type | Naval gun |
| Service history | |
| In service | 1917–1945 |
| Used by | Royal Navy Royal Canadian Navy Free French Navy |
| Wars | World War I World War II |
| Production history | |
| No. built | 2,382 |
| Specifications | |
| Mass | 2 tons barrel & breech |
| Barrel length | 180 inches (4.572 m) bore (45 calibres) |
| Shell | 31 pounds (14.1 kg) |
| Calibre | 4 inches (101.6 mm) |
| Breech | Welin interrupted screw |
| Elevation | -10 degrees to +30 degrees |
| Rate of fire | 10-12 rpm |
| Muzzle velocity | 800 metres per second (2,600 ft/s) |
| Maximum firing range | 12,660 metres (13,850 yd) |
The BL 4-inch Mk IX naval gun was a British medium-velocity naval gun introduced in 1917 as secondary armament on the Renown-class battlecruisers and Glorious-class "large light cruisers", but which served most notably as the main armament on Flower-class corvettes throughout World War II.