QF 18-pounder gun

The Ordnance QF 18-pounder, or simply 18-pounder gun, was the standard British Empire field gun of the First World War era. It formed the backbone of the Royal Field Artillery during the war, and was produced in large numbers. It was used by British Forces in all the main theatres, and by British troops in Russia in 1919. Its calibre and shell weight were greater than those of the equivalent field guns in French and German service. It was generally horse drawn until mechanisation in the 1930s.
The first versions were introduced in 1904. Later versions remained in service with British forces until early 1942. During the interwar period, the 18-pounder was developed into the early versions of the Ordnance QF 25-pounder, which would form the basis of the British artillery forces during and after the Second World War in much the same fashion as the 18-pounder had during the First.

History

During the Second Boer War, the British government realised that its field artillery was being overtaken by the more modern "quick-firing" guns of other major powers, and investigated replacements for its existing field gun, the BL 15-pounder 7 cwt. In 1900, General Sir Henry Brackenbury, the then director-general of ordnance, sent officers to visit European gun makers. At Rheinische Metallwaren und Maschinenfabrik in Düsseldorf, they found a quick firing gun designed by Heinrich Ehrhardt with a recoil system that totally absorbed all the recoil of firing. 108 guns, and spare parts, were secretly purchased and entered service as the Ordnance QF 15-pounder in June 1901.
At the same time, the British Cabinet ordered Field Marshal Lord Roberts, the Commander-in-Chief in South Africa, to send home artillery brigade and battery commanders "selected for their eminence and experience" to form an Equipment Committee. The committee was chaired by General Sir George Marshall, who had been artillery commander in South Africa. It formed in January 1901 with a wide-ranging area of study from horse-drawn mobile guns and the larger more static field guns, to harness design, and even binoculars. They swiftly established the "conditions to be fulfilled by proposed new equipment"; the most important were the "weight behind the team", then ballistics, rapidity of fire, weight of shell, provision of shield and number of rounds carried.
British gun manufacturers were invited to propose designs. Of the many entries, five for the horse artillery gun and three for the field gun were selected and their makers invited to submit a "specimen". These were tested in 1902, but none was found suitable for service although they all had good features. The makers were called to a conference and agreed to collaborate to produce a composite design. This used the Armstrong gun, Vickers' recoil system, and Royal Ordnance Factory's sighting and elevating gear and ammunition carrying. Reduced wheel size from to was also accepted which saved weight. Four Artillery batteries of the composite design took part in trials of in 1903, and the new 18-pounder design was accepted.
The cost of rearmament was huge, and it took some pressure from the press for the War Office to follow through. Initially the British Indian Army was re-equipped first; however, the First Moroccan Crisis changed the priorities. In the end the weapon phase-in cost £4 million and became the biggest such undertaking to the date in British Army history.
The 18-pounder was used on all fronts during the First World War. It remained in service during the inter-war period. Starting in 1938, carriages Marks IV and V were converted to 25-pounder Ordnance QF Mark 1 on Carriage Mark 1. 18-pounder Guns served with the British Expeditionary Force in France in the Second World War and were used in other theatres as well as for training or beach defence.

Description

The 18-pounder was a quick-firing horse-drawn field gun designed to be towed behind a limber and six horses. The gun barrel was wire-wound nickel-steel with a single-motion screw breech with a cartridge extractor. It fired a fixed round of shell and cartridge fixed together, which was known as "quick firing" in British terminology. The lower carriage comprised a single hollow steel trail fixed to the centre of the axle-tree. The limited traverse saddle supported the elevating mass and a shield. Traverse controls were on the left and elevation on the right of the saddle. Recoil was by a hydraulic buffer with telescopic running-up springs to return the barrel to its firing position.
The Equipment Committee's conditions required tangent sights with the option of a telescope. However, the 18-pounder entered service with rocking bar sights – open sights with the option of a telescope on the left and a range scale on the right of the cradle. These arrangements also incorporated independent line of sight, meaning that the sights could remain laid on the target while the barrel was elevated or depressed. A clinometer was provided for indirect fire when the sight was aimed using a gun-arc and aiming posts in line horizontally with the target.
In 1906 indirect fire goniometric sights were adopted which consisted of an alidade mounted on a circular scale graduated in degrees that was mounted on the shield. In 1910, the Number 3 Dial Sight, a refined version with a telescope and compass, replaced the goniometer. The rocking bar and telescope were retained for direct fire, as was the range scale on the right in spite of a clinometer being part of the Dial Sight mount.
In 1910, after three years of trials, the Number 7 Dial Sight was adopted. This was a very heavily modified version of the German Goertz panoramic sight. This, with its sight mount that again included a sight clinometer, replaced the No 3. However, resolving various issues, notably with the sight and mount carrying case mounted on the shield, meant that the Number 7 sight did not enter service until early in 1914.
Unusually for a 20th-century British gun, the 18-pounder retained two-man laying throughout its life, elevation was set on a range scale on the righthand side of the cradle. The Equipment Committee had also insisted on better methods of fuze setting, important because until late in 1914 it only had time fuzed ammunition. A hand held mechanical fuze setter was developed, and in early 1914 a "fuze indicator" was introduced, this converted the range into a fuze setting.

Mk I Gun on Mk I Carriage

The Ordnance Quick Firing 18-pounder Mark I gun barrel was wire-wound for one-third of its length, chosen as it was lighter, stronger and cheaper to manufacture than a fully built-up barrel. A jacket was shrunk over the wire and "A" tube. The Mk I gun and Mk I carriage were accepted into service on 30 June 1904.
The narrow single-pole trail design of the Carriages Mk I and II were suited to towing by teams of horses, but constrained downward motion of the breech, and thus limited the gun's range to 6525 yards in normal use. The range could be increased to 7800 yards by "digging in" the end of the pole trail to increase elevation. Its distinguishing feature was the barrel, significantly longer than the 13-pounder's and, unlike the 13-pounder, the barrel was significantly longer than the recuperator housing above it.

Mk II Gun on Mk I Carriage

The original gun design was quickly replaced in production from 1906 by the "rationalized" Mark II gun for ease of relining : the exterior of the inner "A" tube was slightly tapered, and was inserted into a matching tapered jacket by hydraulic pressure.
Mark I and II guns were still in use in the post-First World War era, and some saw combat in the Far East in Second World War.

Mk II Gun on High-angle Anti-aircraft mounting

In early 1915, a number of 18-pounder guns were mounted on pedestals, with the addition of a second recuperator and retaining catch for the cartridge case at high angle, in an attempt to come up with a workable anti-aircraft gun. The gun's relatively low muzzle velocity, and the unsatisfactory ballistic characteristics of its shrapnel shell at high angles, made it a marginal performer in such a role. However, by sleeving the barrel down to and mating the 18-pounder cartridge with the 13-pounder's shell, the successful QF 13-pounder 9 cwt anti-aircraft gun was produced with the necessary high muzzle velocity.
The early versions of 18-pounder anti-aircraft guns remained in service, apparently only in the home defense of Britain. 35 were in service in Britain in June 1916 and 56 at the end of the First World War. After the war, they were converted back to field gun use by removing the cartridge retaining catch.

Mk II Gun on Mk I Carriage with armoured oil reservoir on recuperator

Battlefield experience in 1914 and 1915 showed up the weakness of the original recuperator springs and loss of oil in the recuperator under intense firing. Poor quality of wartime manufacture of the springs was also a factor. Spring shortages due to breakages meant guns remained in the firing line and had to be "run up" – have the barrel moved forward into its firing position – by hand, hence slowing the rate of fire. A temporary preventive measure was the addition of a distinctive armoured box-shaped oil reservoir to the front end of the recuperator to maintain the oil supply and extend spring life. This modification is visible in many photographs of 18-pounders in action on the Western Front right up to the end of the war

Mk I* and II Carriage

The recuperator spring problem was rectified with the new Mk II carriage officially introduced in the field in November 1916 with a hydro-pneumatic recuperator design which replaced the recuperator springs with a system driven by air compression and could be fitted into the existing spring housing by battery officers in the field. It is identified by the torpedo-shaped extension on the recuperator, which made the recuperator assembly nearly as long as the barrel and hence altered the equipment profile. Converted existing carriages were designated Mk I*. The Mk II carriage also incorporated a longer cradle.
In about 1917, all 18-pounders began to be fitted with a new calibrating range scale. This allowed the gun's muzzle velocity to be set on it and automatically corrected the range for the difference between the actual muzzle velocity and the standard one.