| Ordnance QF 12 pounder 12 cwt anti-aircraft gun | |
| Origin: | United Kingdom |
| Is Ranged: | yes |
| Is Artillery: | yes |
| Is Uk: | yes |
| Service: | 1914–1918 (as land AA gun) |
| Design Date: | 1893 |
| Variants: | Mk I, Mk II |
| Caliber: | 3 inch (76.2 mm) |
| Cartridge: | Fixed or separate QF |
| Max Range: | [1] |
| Breech: | single-motion screw |
| Recoil: | Hydro-spring, constant, |
| Elevation: | 0° - 85° |
| Traverse: | 360° |
The 12 pounder 12 cwt anti-aircraft gun was a British anti-aircraft gun of the First World War, The guns were QF 12 pounder 12 cwt naval guns taken from coast defence positions with the addition of a modified cradle for higher elevation, a retaining catch for the cartridge, and an additional spring recuperator above the barrel and high-angle sights. Writers commonly refer to it simply as "12 pounder anti-aircraft gun". 12 cwt referred to the weight of the barrel and breech - - to differentiate it from other 12-pounder guns.
When World War I began Britain had no anti-aircraft artillery and had given little thought to it. Hence in 1914 when Germany occupied parts of Belgium and northern France, it faced the risk of air attack, and various medium caliber guns were adapted to high-angle mountings, including the 12 pdr 12 cwt. All QF 12 pounder ammunition at the time was "Separate loading QF" i.e. the propellant came in a brass cartridge case with primer ready installed, but the shell was loaded separately. For anti-aircraft firing, Fixed QF rounds were quickly developed i.e. with the shell already attached to the cartridge case. This allowed slightly faster loading.
For home air defence the gun was typically mounted on a high-angle mounting with an additional spring recuperator above the barrel, on a 2-wheel towed travelling platform, × The 4 stabilizing arms at the corners were swung out, rods at the ends screwed down to lift the platform off the wheels which were then removed and the platform lowered to the ground.[2] It was also deployed on static mountings to defend prominent targets such as dockyards.
While the gun was much lighter than the QF 3 inch 20 cwt AA gun, for anti-aircraft use it lacked its range and shell weight. Hence the 3 inch 20 cwt gun became the preferred heavy AA gun on land and ships from 1914 to 1937. The 12 pdr 12 cwt also proved only marginally superior to the much lighter QF 13 pounder 9 cwt as a light AA gun. Comparison:[3] -
| Gun | Muzzle velocity | Shell weight | Time to at 25° (seconds) | Time to at 40° (seconds) | Time to at 55° (seconds) | Max. height[4] | |
| 13-pdr 9 cwt | 10.1 | 15.5 | 22.1 | ||||
| 12-pdr 12 cwt | 9.1 | 14.1 | 19.1 | ||||
| 3-inch 20 cwt 1914 | 8.3 | 12.6 | 16.3 | ||||
| 3-inch 20 cwt 1916 | 9.2 | 13.7 | 18.8 | [5] |