12 pdr Coast Defence Gun

12 pdr coast gun

The 12 pdr Coast Defence Gun originated in 1894 as a naval gun for defence against fast, light craft. It remained in service, with minor modifications, until 1956. One aspect of the original cartridge was odd in that it had a protruding electric primer. It could be replaced by a similar adapter to take an electric or precussion tube. This resulted in the breech block being recessed to fit around this primer block. After firing, the case was extracted by a gun number using a forked hook on the rim of the primer to pull the cartridge case from the breech. This sytem was replaced in 1935 by conventional extractors engaging the cartridge rim, although some older guns remained in service.

The mounting was a simple pedestal and a shield. Early guns had gear driven elevation and traverse. Later this was changed to a free swinging traverse. The layer hooked his arm over an arm piece and swung the gun round. Virtually obsolescent by 1939, a large number were brought from store and emplaced around the coast in 1940. These were additional to those already in place in fixed defences.


Mark-1*Converted to Anti-Aircraft use in WW1. Re-converted to coast use later
Mark-1**Mark-1* converted to Mark-4 standard with automatic extraction
Mark-1***Mark-1* converted to Mark-4 standard
Mark-4New pattern extractor & breech carrier to allow automatic extraction.
Introduced in 1935
Marks-2, 3 & 5Naval service


Mark-1Shield & pedestal with 18 holding down bolts
Mark-2As Mark-1 but with shorter elevating arc, simpler shield & pedestal design.
Weight in action 6,328 lbs
Mark-3As Mark-2 but lighter and minus the geared traverse. Weight in action 5,432 lbs


Weight of gun & breech mechanism1,395 lbs
Total length123.6 inches
Length of bore120 inches (40 calibres)
(guns were brought up to new standards when going for periodic re-furbishing)
Originally increasing, right hand, 1/120 at breech – 1/28 at muzzle
Then straight grooves to 83.035 inches from muzzle & increasing to 1/30 at muzzle
Finally uniform, right hand, 1/30
Breech mechanismInterrupted screw, single motion, electric & percussion fired
Recoil systemHydro-spring 12 inches
Elevation-15° to +20°
Weight in action9,240 lbs
Rate of fire15 rounds per minute


Firing standard 12 lb 8 oz HE shell

Muzzle velocity2,257 feet/second
Maximum range10,100 yards


Shell QF 12 pdr HE Mark-5Forged steel shell with Fuze Percussion DA No.44 or 45
Shell QF 12 pdr CP Mark-5Pointed shell with Fuze Base No.12F Special for penetration of light structures
Shot QF 12 pdr Practice Mark-3Plain steel shot simulating the common pointed shell for practice
Cartridge QF 12 pdr 12 cwt Mark-3Brass case with igniter at the base. An adapter was screwed into the base taking a Tube Vent Electric. In the event of failure of the firing circuit a Tube Percussion could be fitted instead
The Royal Artillery 1939-45