After World War 1 it became obvious that the speed of naval attacks had increased, so there was now a need for a light, fast firing gun to defend harbours. After looking at the naval 2 pdr pom-pom, the committee decided that the shell was too light but the rapid fire solution was correct. In 1925, a design for a twin barrelled 6 pdr was put forward as the Twin 6 pdr Coast Gun. The mounting had 2 guns side by side controlled by 2 layers, taking their data from dials fed by an off mount Director & Range Finder. The guns were loaded & fired independently by 2 teams. Using semi-automatic breeches it could reach a rate of 40 rounds per minute for each gun.
Laying was continuous so, having loaded, the gun could be fired as soon as the breech closed. The barrells were normally parallel but the gun captain could converge the fire once a hit had been achieved from one barrell.
The first guns were proved in 1928 and full trials then took place. Manufacture did not start until 1933. The first equipments were formally approved in February 1934. The design remained in service until 1956.
The gun was known as the 6 pdr 10 cwt to distinguish it from the Anti-Aircraft 6 pdr 6 cwt and the Anti-Tank 6 pdr 7 cwt.
Gun
| Mark 1 | Basic model as described above |
| Mark 1/1 | Mk1 modified having breech ring mortise radiussed to prevent cracking during sustained fire (post war) |
| Mark 2 | As Mk1 but monobloc instead of loose liner construction |
| Mark 2/1 | Mk2 modified having breech ring mortise radiussed to prevent cracking during sustained fire (post war) |
Mounting
| Mark 1 | Basic model |
| Mark 1* | Mk1 converted to approximate to Mk3 |
| Mark 2 | Mk4 altered to be semi-mobile |
| Mark 3 | As Mk1* but new manufacture |
| Mark 4 | As Mk1 but fitted with 6pdr 6cwt guns |
Data
| Weight of Gun & Breech Mechanism | 1,060 lbs |
| Total Length | 109.72 inches |
| Length of Bore | 105.47 inches (47 calibres) |
| Rifling | 24 grooves, uniform right hand 1/30 |
| Breech Mechanism | Verical sliding block, semi-automatic, percussion fired |
| Elevation | -10° to +7½° |
| Traverse | 360° |
| Recoil System | Hydro-spring, constant, 6 inches |
| Weight in Action | 22,132 lbs |
| Rate of Fire | 120 rounds per minute |
Performance
Firing standard 6.25 lbs HE Shell
| Muzzle Velocity | 2,360 feet/second |
| Maximum Range | 5,150 yards |
Ammunition
Fixed, case charge
| Cartridge, HE, Shell, 6pdr 10cwt Mark 8 | The cartridge comprised the Shell HE Mk10T, Fuze Percussion No.244 & the propelling charge. |