Twin 6 pdr Coast Gun

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. 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 1Basic model as described above
Mark 1/1Mk1 modified having breech ring mortise radiussed to prevent cracking
during sustained fire (post war)
Mark 2As Mk1 but monobloc instead of loose liner construction
Mark 2/1Mk2 modified having breech ring mortise radiussed to prevent cracking
during sustained fire (post war)

Mounting

Mark 1Basic model
Mark 1*Mk1 converted to approximate to Mk3
Mark 2Mk4 altered to be semi-mobile
Mark 3As Mk1* but new manufacture
Mark 4As Mk1 but fitted with 6pdr 6cwt guns

Data

Weight of Gun & Breech Mechanism1,060 lbs
Total Length109.72 inches
Length of Bore105.47 inches (47 calibres)
Rifling24 grooves, uniform right hand 1/30
Breech MechanismVerical sliding block, semi-automatic,
percussion fired
Elevation-10° to +7½°
Traverse360°
Recoil SystemHydro-spring, constant, 6 inches
Weight in Action22,132 lbs
Rate of Fire120 rounds per minute

Performance

Firing standard 6.25 lbs HE Shell

Muzzle Velocity2,360 feet/second
Maximum Range5,150 yards

Ammunition

Fixed, case charge

Cartridge, HE, Shell, 6pdr 10cwt Mark 8The cartridge comprised the Shell HE Mk10T,
Fuze Percussion No.244 & the propelling charge.