Ordnance BL 12-in Howitzer Mk II and IV

The Ordnance BL 12in Siege Howitzer Mk.II and Mk IV were road portable versions of a weapon based on the smaller 9.2in BL Siege Howitzer.

By 1915 it was clear that the Royal Artillery would need larger guns to deal with the problems of trench warfare. Two versions of a 12in siege howitzer were ordered, one to be used as a railway gun and the other as a road portable weapon. The design of the road portable version was carried out by Vickers, who responded by enlarging the 9.2in weapon, keeping most of its layout but at a larger scale.

The 9.2in howitzer came in three parts, but the 12in Mk.II, the first of the road portable versions of the new weapon, needed to be split into six to be transported. One consisted of just the barrel. The second was the cradle, complete with the recoil system. Third was the carriage, made up of two side plates, each roughly triangular in shape. When in use the cradle was carried between these side plates. Fourth was the bed plate. Fifth was a steel box that went in front of the bed plate and had to be filled with up to 20 tons of earth to keep the weapon stable. The sixth included all of the accessories required to service the complex weapon. A series of girder ramps, winches and jacks was designed to make it easier to construct the weapon, but it was still a slow process, and could take at least half a day. The 12in Mk II had a range of 10,370m, just over 1,000m better than the 9in Mk I, but not terribly impressive given the size and complexity of the weapon.

The much improved 12in Mk.IV appeared in 1917. This had a longer barrel, which improved range to 13,120m. An Asbury breech made it quicker to load the gun, as did a power rammer and the addition of more ammunition handling jibs. As a result the rate of fire improved, but the heavy earth box was retained so it still took some time and effort to move the gun. At first the Mk.IV was towed by steam traction engines, but in 1917 heavy trucks replaced them.

Neither type was built in large numbers, with only 14 Mk IIs and forty three Mk IVs being built.

A number of the surviving Mk.IVs went to France with the BEF in 1939, where they became known as the ’12 road hogs’ because of the amount of road space the convoy of six loads took up. When the fighting finally began in May-June 1940, the 12in siege howitzer was proved to be obsolete, too slow moving to cope with the rapid pace of the German attack. They could easily be avoided, and most were either destroyed or captured. A handful survived in Britain and were used on anti-invasion duties and then as training weapons.

In 1943 it was suggested that an anti-concrete shell could be developed form the 12in Howitzer, to allow it to be used against the concrete defences of Hitler’s Fortress Europe. However none of these shells were ever built, and instead air power and other sources of artillery would be used against the German defences. The 12 howitzer was declared obsolete in March 1945.

The Mk.I, Mk.III and Mk.V were all railway guns.

Name

12in BL Siege Howitzer Mk.IV

Calibre

305mm (12in)

Barrel Length

5.65m (18ft 6.5in)

Weight for transport

 

Weight in action

57,915kg (127,680lb) including earth box

Elevation

+20 to +65 degrees

Traverse

60 degrees

Shell Weight

340kg (750lb)

Muzzle Velocity

447ft (1,468m)/ sec

Maximum Range

13,120m (14,350 yards)

Rate of Fire

 

The Illustrated Encyclopedia of Weapons of World War I, general editor Chris Bishop. A useful collection of articles on the main weapons of the First World War, based on Orbis's War Machine of the 1980s. Still accurate despite its relative age, well illustrated and supported by some informative general articles, and provides a good overview of the military technology of the Great War. [read full review]
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How to cite this article: Rickard, J (6 January 2025), Ordnance BL 12-in Howitzer Mk II and IV , http://www.historyofwar.org/articles/weapons_ordnance_BL_12in_howitzer_II_IV.html

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