This was a First World War piece built in three different models. The Marks 3 & 5 survived the war & were placed into storage. They re-appeared in 1939 and a Mark 6 was approved to replace them but it is doubtful that any were made.
The Mark 3 was carried on a drop bed wagon with two 4 wheeled bogies. In action, the wagon was lowered by screw jacks until the side girders rested on the ends of the sleepers. It was then anchored by steel cables to stop it sliding when firing. There was no sideways bracing so it could only be fired within 20° of the track centre line. Therefore curved track was necessary to give a reasonable zone of fire.
To overcome this problem the Mark 5 was introduced in July 1917. It was ballistically the same as the Mark 3 but had a new design of recoil system and cradle. The mounting was higher and with a loading platform. Outriggers were provided for stabilizing the mounting when firing across the track.
A number of these guns went to France in 1939 but were left there in 1940. The few that remained in the UK were deployed for anti-invasion duties. They were declared obsolete in August 1945.
| Mk 3 | Elswick design. Continuous motion breech mechanism, Trunnions set well back. |
| Mk 3A | Approved 1940 as replacement for Mk3. Similar design with loose liner. Doubtful any were built |
| Mk 5 | Similar to Mk3 with less weight at breech end. |
| Mk 5A | Approved 1940 as replacement for Mk5. Loose liner. |
| Mk 6 | Approved 1940 as replacement for Mk3A. Simpler construction, lighter weight |
Mountings
| Mk 2 | 2 bogie rail truck with barbette mounting. Fired between 40° & 60° elevation only. All round traverse but only fired between 20° left & right. Loading angle 3½°. |
| Mk 3 | Same truck but higher mounting with loading platform. Fired between 0° & 45° (reduced charge used up to 20°). 2 speed elevating gear. Loading angle 0° |
Data
12 inch Howitzer Mk 3, on Mounting Mk 2, on Truck, Railway, Mk 2
| Weight of Gun & Breech Mechanism | 25,221 lbs |
| Total length | 225.3 inches |
| Length of bore | 207.6 inches (17.3 calibres) |
| Rifling | 60 grooves, uniform right hand 1/15 |
| Breech mechanism | Interrupted screw, continuous motion, percussion fired |
| Elevation | 0° to +65°. Minimum firing angle 40° |
| Traverse | 360° but only fired within 20° left & right of centre line |
| Recoil system | Hydropneumatic. Constant 30 inches |
| Weight in action | 136,080 lbs |
12 inch Howitzer Mk 5, on Mounting Mk 3, on Truck, Railway, Mk 3
| Weight of Gun & Breech Mechanism | 23,646 lbs |
| Total length | 225.3 inches |
| Length of bore | 207.6 inches (17.3 calibres) |
| Rifling | 60 grooves, uniform right hand 1/20 |
| Breech mechanism | Interrupted screw, continuous motion, percussion fired |
| Elevation | 0° to +45°. Minimum firing angle 20° |
| Traverse | 120° left & right |
| Recoil system | Hydropneumatic. Constant 60 inches |
| Weight in action | 170,143 lbs |
Performance
Firing standard 750 lb HE Shell
| Muzzle Velocity | 1,468 feet/second |
| Maximum Range | 14,350 yards |
Ammunition
Separate loading Bag Charge
| Shell, HE, Mk 10 | Nose fuzed, non streamlined. Used Fuze Percussion, No. 106 or 106E |
| Shell, Common Pointed, Mk 1A | Non streamlined, pointed shell. Base Percussion Fuze No. 16. For hard targets (buildings, dugouts etc). |
| Shell, Concrete Piercing, Mk 1 | Never entered service |
| Propelling Charge | This was divided into 2 sections. A short range portion with Charges 1 to 6 & a long range portion , charges 7 to 11. Each portion had a base charge (1 & 7) with increments to bring the weight of cordite up to the required weight. |