Armstrong gun

British artillery piece

An Armstrong gun was a uniquely designed type of rifled breech loading field and heavy gun designed by Sir William Armstrong and manufactured in England beginning in 1855 by the Elswick Ordnance Company and the Royal Arsenal at Woolwich. Such guns involved a built up gun construction system of a wrought iron (later of mild steel) tube surrounded by a number of wrought iron strengthening coils shrunk over the inner tube to keep it under compression.

In 1854, Armstrong approached the Secretary of State for War, proposing that he construct a rifled breech loading 3 pounder gun for trial. Later increased in bore to 5 pounder, the design performed successfully with respect to both range and accuracy. Over the next three years he developed his system of construction and adapted it to guns of heavier calibre. Armstrong's system was adopted in 1858, initially for "special service in the field" and initially he only produced smaller artillery pieces, 6 pounder (2.5 in/64 mm) mountain or light field guns, 9 pounder (3 in/76 mm) guns for horse artillery, and 12 pounder (3 inches /76 mm) field guns. Armstrong did not consider his system suited to heavier guns but higher authorities had him develop a 20 pounder (3.75 inches /95 mm) field & naval gun, a 40 pounder siege gun, and a 110 pounder (7 inches /180 mm) heavy gun. The Royal Navy used all these guns and all except the 20 pounder saw service in New Zealand.

The British used Armstrong guns extensively to great effect in the Second Opium War. As reported by the translator Robert Swinhoe, after the British attack on the Chinese fort at Pehtang:

Numbers of dead Chinese lay about the guns, some most fearfully lacerated. The wall afforded very little protection to the Tartar gunners, and it was astonishing how they managed to stand so long against the destructive fire that our Armstrongs poured on them; but I observed, in more instances than one, that the unfortunate creatures had been tied to the guns by the legs. The Armstrong gun—mainly the 12 pounder—was used extensively in the 1863 conflict in New Zealand between British troops and Maori in the Waikato. A well preserved 12 pounder which was used in the battle of Rangiriri is at the Te Awamutu museum. The barrel can traverse 6 degrees left or right without moving the gun carriage. The wheels are wooden with a 75 mm wide steel band. The wheel diameter is 1.7 m. The track width is 1.8 m. Barrel width at the muzzle is 140 mm. Such was the confidence of the army in the accuracy of the gun that at the battle of Hairini Ridge the artillery was fired over the heads of the advancing infantry as they stormed the ridge. The infantry took cover in a slight depression in the ground in front of the Maori trenches and then stormed the trenches when the shelling stopped. On July 4, 1868, Armstrong guns were used at the Battle of Ueno by forces supporting the Imperial government of Japan. Armstrong guns were used against British and Indian troops during the Second Anglo Afghan War in the Battle of Charasiab, in which Howard Hensman describes six being captured by a combined Anglo Indian expedition under the command of Brigadier General Baker.

In 1863 an Ordnance Select committee met to consider the merits of muzzle loading and breech loading guns. In 1864, even before they had concluded their investigations, the Government stopped the manufacture of Armstrong breech loaders. When the Committee finally reported, in August 1865, they announced that:

The many grooved system of rifling with its lead coated projectiles and complicated breech loading arrangements is far inferior for the general purpose of war to the muzzle loading system and has the disadvantage of being more expensive in both original cost and ammunition. Muzzle loading guns are far superior to breech loaders in simplicity of construction and efficiency in this respect for active service; they can be loaded and worked with perfect ease and abundant rapidity. Their report did admit that Armstrong's guns, while more expensive, were undoubtedly safer in that while it was not uncommon for cast iron muzzle loaders to burst, not one Armstrong gun had ever done so. (Furthermore, gunners could clear a misfire from the breech; when the RML 17.72 inch gun at Napier of Magdala Battery at Gibraltar misfired, a gunner had to be lowered head first down the bore to attach an extractor to the shell.) Despite a further report which remarked on the advantages of breech loaders, cost dominated the proceedings and the Committee finally announced that "The balance of advantages is in favour of muzzle loading field guns", and in 1865 Britain reverted from breech loading ordnance to muzzle loading. Tests conducted in 1859 with the Armstrong 40 pounder, and again in 1869 with the Armstrong rifled 100 pounder had demonstrated that neither rifled cannon was capable of penetrating 4 inches of armour, even at as little as 50 yards. This was crucial because Britain, as a maritime power, relied for its security on the ability of its naval ordnance to defeat any new armour protected warships being developed by potential enemy powers. Armstrong developed an alternative horizontal sliding wedge version of his breechloader, for 40 pounder and 64 pounder guns, in an attempt to address the limitations of the screw breech, but the Government had already decided to return to muzzle loading guns. To allow rifling to be used with muzzle loaders, Armstrong proposed in 1866 a new system whereby the shells had studs on the outside, which aligned with grooves in the barrel of the cannon. This was adopted by the Government for the first generation of rifled muzzle loaders, termed "RML", together with Armstrong's built up wrought iron construction method, which was considered sound.

Armstrong returned to the manufacture of breechloaders in the 1880s, using an interrupted thread breech with its own "Armstrong cup" and later the de Bange methods of sealing the bore which relied upon the power of the gun's firing to effect the gas seal ("obturation") rather than the manual labour in the 1858 design. It was a major supplier of modern "BL" guns to the Royal Navy, British Army and the world export market until the 1920s. However, it is its earlier generations of "RBL" guns that are typically referred to as "Armstrong guns".