Ordnance QF 18-pounder field gun Mk IV

The Ordnance QF 18-pounder field gun Mk.IV was a modernised version of the 18-pounder Mk.I, but didn’t enter service until late in the First World War.

The 18-pounder Mk.I used a pole trail, which limited its elevation and thus range, and a recoil system carried above the gun barrel. As the First World War went on, the range of only 5,966m became an increasing problem and the Mk.IV was developed to solve this.

Australian troops
training with
18pdr Mk IV

The most significant change was the use of a box trail, with a gap under the breach, allowing the gun to be elevated to a much higher angle (up to 37 degrees fron only 16), increasing its range from 5,966m to 10,150m. The recoil system was moved to a new position underneath the barrel and the hydro-pneumatic system used on later Mk Is was replaced with a ‘floating piston’ type. This used oil and compressed air and was smoother and more reliable than the older system. A new Asbury type breech was installed. The gun cradle was also modified to cope with the increased strains caused by the new features. The new version had a range of 9,300 yards, an impressive increase of 2,600 yards over the Mk.I.

The Mk.IV entered full production towards the end of 1918. One battery of Mk IVS saw service with the Fourth Army in the last two months of the First World War.

It became the main weapon of the Field Artillery in the inter-war periods, before being replaced by the famous 25-pounder. Around 1,000 18-pounder Mk IVs were used as the basis for the first 25-pounders, the Ordnance 25-pounder Mk I or 18/25 pounder, which had a new 25 pounder barrel on the 18 pounder carriage.

A number of 18-pounders were still in service at the start of the Second World War, and some remained in service with the Irish Army until the 1970s.

By 1940 there were three variants on the gun in service - the Mk IV, Mk IVA and Mk IVB and a wide range of carriages. Many 18-pounders went to France with the BEF, but most were lost during the retreat from Dunkirk and taken into German service.

The Carriage Mk III was the first version of a box trail. These became the 8.38cm FK 271(e) in German service.

The Carriage Mk IV used a hollow box trail. The Mk IVR was the same trail but with rubber wheels. Both types entered German service as the Fk 272(e).

The Carriage Mk V used a split trail, and had a wide range of traverse. The Mk VR was the same trail but with rubber wheels. These entered German service as the 8.38cm FK 273(e).

There was also a Carriage Mark 11PA, the Martin Parry conversion, which allowed old pole trail guns to be towed by motor vehicles. This version was used on home defence duties during the Second World War. 

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]

Books on the First World War | Subject Index: First World War

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