| Ordnance QF 12-pounder 18 cwt | |
|---|---|
 Deployed as anti-aircraft gun on HMS Agamemnon off Salonika, 1916 | |
| Type | Naval gun, Coastal defence |
| Place of origin | United Kingdom |
| Service history | |
| In service | 1906–1921? |
| Used by | Royal Navy |
| Wars | World War I |
| Production history | |
| Designer | Elswick Ordnance Company |
| Designed | 189? |
| Specifications | |
| Mass | Gun & breech: 2,016 lb (914 kg) |
| Barrel length | Bore: 150-inch (3.81 m) (50 calibres) |
| Shell | Separate QF 12.5 lb (5.66 kg) |
| Calibre | 3 in (76 mm) |
| Rate of fire | 20 rd/min[1] |
| Muzzle velocity | 2,600 ft/s (790 m/s)[2] |
| Effective firing range | 9,300 yards @ +20° (8,500 m @ +20°) |
The QF 12 pounder 18 cwt gun (Quick-Firing) was a 3-inch high-velocity naval gun used to equip larger British warships such as battleships for defence against torpedo boats. 18 cwt referred to the weight of gun and breech (18 × 112 lb = 2,016 lb or 914 kg), to differentiate the gun from others that also fired the "12 pound" (actually 12.5 lb or 5.7 kg) shell.
- ^ 20 rounds per minute is quoted in Elswick gun tables of 1901, and may be considered optimistic
- ^ 2600 ft/s: Range Tables for His Majesty's Fleet, 1910 February 1911 with 2 lb 12 oz (1.25 kg) cordite MD propellant. The gun first appears in Elswick gun Tables as quoted in Brasseys Naval Annual 1901 with a maximum muzzle velocity 2800 ft/s with "battering" charge of 3 lb cordite (Mk I), but this is not the charge adopted for British service.