12 inch Railway Howitzer

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 3Elswick design. Continuous motion breech mechanism, Trunnions set well back.
Mk 3AApproved 1940 as replacement for Mk3. Similar design with loose liner.
Doubtful any were built
Mk 5Similar to Mk3 with less weight at breech end.
Mk 5AApproved 1940 as replacement for Mk5. Loose liner.
Mk 6Approved 1940 as replacement for Mk3A. Simpler construction, lighter weight

Mountings

Mk 22 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 3Same 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 Mechanism25,221 lbs
Total length225.3 inches
Length of bore207.6 inches (17.3 calibres)
Rifling60 grooves, uniform right hand 1/15
Breech mechanismInterrupted screw, continuous motion,
percussion fired
Elevation0° to +65°. Minimum firing angle 40°
Traverse360° but only fired within 20° left & right of
centre line
Recoil systemHydropneumatic. Constant 30 inches
Weight in action136,080 lbs

12 inch Howitzer Mk 5, on Mounting Mk 3, on Truck, Railway, Mk 3

Weight of Gun & Breech Mechanism23,646 lbs
Total length225.3 inches
Length of bore207.6 inches (17.3 calibres)
Rifling60 grooves, uniform right hand 1/20
Breech mechanismInterrupted screw, continuous motion,
percussion fired
Elevation0° to +45°. Minimum firing angle 20°
Traverse120° left & right
Recoil systemHydropneumatic. Constant 60 inches
Weight in action170,143 lbs

Performance

Firing standard 750 lb HE Shell

Muzzle Velocity1,468 feet/second
Maximum Range14,350 yards

Ammunition

Separate loading Bag Charge

Shell, HE, Mk 10Nose fuzed, non streamlined. Used Fuze Percussion,
No. 106 or 106E
Shell, Common Pointed, Mk 1ANon streamlined, pointed shell. Base Percussion
Fuze No. 16. For hard targets (buildings, dugouts etc).
Shell, Concrete Piercing, Mk 1Never entered service
Propelling ChargeThis 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.