The 100-ton gun (also known as the Armstrong 100-ton gun) was a British coastal defense gun and is the world's largest black powder cannon. It is a rifled muzzle-loading (RML) gun made by Elswick Ordnance Company, the armaments division of the British manufacturing company Armstrong Whitworth, owned by William Armstrong. The 15 guns Armstrong made were used to arm two Italian battleships and, to counter these, British fortifications at Malta and Gibraltar.
Origins Around 1870, the largest gun made by UK firms was the 320 mm RML (rifled, muzzle-loading) gun, with a mass of 38 long tons (38.6 t), firing an projectile capable of piercing of mild steel at .,This weapon was adequate for the needs of the time, but the progress of gun technology was very rapid. French industries soon made a , gun. This led the Royal Navy to ask for an gun.
Armstrong, the main British artillery producer, began a project for creation of an even larger weapon, an gun, also called the '100 ton'. Armstrong offered it to the Royal Navy, which rejected the gun, deeming it too heavy and costly.
Description
General characteristics
The 100 ton gun was enormous for its time. The weight was comparable to that of the much later Iowa-class /50cal guns, even though their barrels were quite short. They were muzzle-loading guns, with a rifled tube and rigid mount. Each gun required a crew of 35 men, including 18 men to handle the ammunition.
First build The 100-ton gun was first built with a caliber of throughout the whole length of its bore. It was (L/23.5) long. The barrel's outer diameter was at the breech, which reduced to at the muzzle. The length of bore was long, or 21.5 calibers. The rifling consisted of 27 grooves of 1/8-inch depth and had a progressive twist rate of L/45 at the muzzle. The driving bands of the shells were attached gas-checks instead of the traditional studs. The weight of the gun was , or about 100 tons.
The gun was built up from an inner steel tube surrounded by multiple wrought iron coils. The inner tube itself consisted of two parts joined by a double ring. This was caused by the manufacturer being unable to make this in one piece.
The loading gear of the gun was hydraulic. In a fixed position, the barrel was declined to bring in the charge and a ram head then forced the shot up the bore to its seat against the charge. After firing, the gun was again brought back to this position. The ram, which had a sponge head, would then be brought in again. When it reached the back of the gun it would unleash a powerful jet of water to clean the barrel and make sure no fire was left. Once the ram had been withdrawn, a new charge and shot were brought up in turn and positioned before the barrel. The whole operation was handled by a man pulling levers.
Firing was mechanical or electrical, with an optical system for aiming.
The gun crews could fire a projectile once every six minutes. Muzzle velocity was and maximum elevation was 10° 30'. At maximum charge ?) and maximum elevation, a projectile could achieve a range of only , but at that distance the projectile could still pierce of steel (it is not clear if it was mild or hardened).
The weight of the mount was: (mobile mounts with 18 wheels), (platform) and (base). The platform was sloped at 4 degrees to slow the recoil. On the platform mount, hydraulic systems powered chains that traversed the guns through an arc of 150 degrees; another hydraulic system provided elevation.
Re-chambering After tests in Italy, the first gun was returned to the factory to get a caliber of and a powder chamber with a diameter of . Chambering was a recent innovation and gave this gun an about 35% larger charge chamber. In theory, a larger chamber allowed a higher charge without raising peak pressures. However, as boring up the chamber reduced the gun's strength, the gun was strengthened near the front of the chamber. This was done while retaining the same weight. Another innovation was the use of shallower polygonal rifling. All other guns were directly built to incorporate these changes.
Ammunition This was a second-generation RML gun, equipped with polygroove rifling and firing only studless ammunition with automatic gas-checks for rotation.
Projectiles were of three types, all weighing and having a diameter of 17.7 inches (450) mm: Armour-piercing (AP) Palliser, 44 inches (1.12 m) long, steel forward section, capable of piercing of steel at 2,000 yd (530 mm at 1,800 m). with a 32-pound (14.5 kg) explosive internal charge. High explosive (HE) Common, long, with thinner walls and a HE charge. Shrapnel shell: long, with a charge of only HE, but also 920 bullets of each.
Firing charges were polygonal in shape, with 399 x 368 mm maximum width and length. They were made of 1 cwt () 'Large Black Prism' propellant, and four or five were needed for every shell fired at maximum power. The recoil was as two hydraulic pistons in the rear part of platform absorbed the remaining energy.
Italian service
The Italian order
After the reunification of Italy, the Regia Marina began an innovative program to field the best and most powerful battleships of the time, the first being the Duilio-class, armed with 380 mm guns. They were already very powerful, but in February 1874 when the UK started to build HMS Inflexible, armed with guns, Italian admirals called for even more powerful guns, to hold the lead in battleship design.
On 21 July 1874, Armstrong signed a contract with Italy to deliver eight of its 100-ton guns, enough to arm Duilio and her sister-ship Dandolo.
Transport The order of the 100-ton gun is closely linked to the construction of the Swing Bridge over the River Tyne in Newcastle upon Tyne. This hydraulic swing bridge was also built by Armstrong and at the time, it was the largest of the world. On 17 July 1876, it was opened by the Italian Navy steamer Europa, which came to collect the first 100-ton gun.
In La Spezia, a special 160t crane had been built at the arsenal to handle the 100-ton gun. This was a steam driven hydraulic crane designed by George Wightwick Rendel, the first of Italy.
Tests at La Spezia
The Italian Navy tested the 100-ton gun at Muggiano near La Spezia. Here the 100-ton gun was mounted on a 26 by 16 m iron pontoon which stuck out 1 m above the waterline. The pontoon was docked in a basin close to shore. Elevation and declination of the gun was done by hydraulics, powered by a steam engine. The pontoon allowed the gun to turn in the absence of a turret.
The setup with the pontoon was inspected by George Rendel and Captain Noble, partners in the Armstrong firm. Noble was also a known expert on gas pressures in cannon. Some other British visitors were Col. Younghusband of the Woolwich arsenal and Col. Brakenbury of the London Times.
Some preliminary shot were fired on 20, 22, and 23 October 1876. On the third day, velocity measurements finally worked. With a charge of , a shot of got a velocity of .
The tests against armor targets drew international attention. The targets were indeed mock-ups of ship hulls placed on embankments in a ravine. The first target had two long and wide Creusot steel plates, placed one above the other. Each was thick and backed by two layers of teak collectively thick. Behind that was an iron skin and behind that, frames, representing those of a ship. These steel plates were reported to be of very soft steel, meaning that its ductility was supposed to keep it from fracturing.
The second target was similar in every respect. Above, it had a wrought iron front plate by Cammell of Sheffield, below that was a wrought iron plate by Marrell. The third target was of the same dimensions. However, the upper half was made up of two Cammell wrought iron plates of 12 and 10-inch, with 14-inch of timber in between. The lower half contained a 14-inch chilled cast iron plate in the back and an 8-inch wrought iron plate in front. The fourth target was like the third, but with plates made by Marrell and timber in between the wrought and chilled iron plates. The total thickness of all four targets was the same at .
The raft with the 100-ton gun was about 110 m from the targets. Other guns that participated in the test were a RML 11-inch 23-ton gun and two RML 10-inch 18-ton gun. As these were about 80 m from the target, the range of the guns was almost the same. The smaller guns were placed so that they could be moved sideways to allow the big gun to fire.
On 25 October, the 10-inch gun fired at the upper half of the steel target. The shot penetrated only into the first plate, but a few seconds later the plate 'began to sing' and cracks began to extend from the hole. The Cammell and Marrell wrought iron plates resisted the 10-inch gun. Later, the 10 and 11-inch guns defeated the steel target. The day ended with the 100-ton gun firing towards the sea. On the 26th, it fired against the untouched Creusot plate and completely destroyed it. However, the shot broke up and did not get through the target.
While experts concluded that steel was unsuitable for armor, they were puzzled by the cracks from the lighter shot. During the next days, the 100-ton gun fired at the iron targets. These plates were not reduced to pieces. However, the projectiles went straight through with a remaining velocity of about and made a very large rent in the iron plates. It meant that the iron vs. steel discussion was again open. In mid-November 1876, Nathaniel Barnsby, Director of Naval Construction to the Royal Navy was to go to La Spezia to study the results and the merits of using steel.
A detailed overview with illustrations of these tests was published. The 100-ton gun fired 39 shot from 20 October to 8 November 1876. The gunpowder used for most shot was the English government Waltham Abbey gunpowder of 1.5 inch cube, although some shots were done with less offensive Fossano gunpowder. The highest observed pressure was 20.8 ton per square inch or 3,170 atm with a charge of and a velocity of 443 m/s.
Pressures were quite irregular, with some higher charges yielding lower peak pressures. Overall, this led the representatives of Armstrong to propose a maximum charge of 145 kg or 300 lb. This gave a velocity of 434 m/s, which was well above the contracted velocity of 423 m/s with a pressure of 2,800 atm.
Test of the chambered gun After the first chambered guns had been made, one of these was tested in La Spezia in March and April 1878. This time 85 shot would be fired. There were three goals: First to collect ballistic data while firing with the British powder, and compare this with the data of the original gun; Secondly to test the Italian Fossano gunpowder and compare it with the English P2 powder; Thirdly, to determine the best form of cartridge and the best means to ignite it.
With the proper charges and a projectile of , the original gun had given a velocity of at a pressure of 18.3 tons per square inch. For the chambered gun, this was at a pressure of 17 tons per square inch. This meant that chambering had increased the energy of the gun by about 25%.
The Fossano gunpowder also seemed very effective. Three rounds were fired with an average charge of of English powder and of Fossano powder. On average, the Fossano gunpowder increased the energy of the gun by about three percent while it reduced pressure by about 4 tons per square inch. While the English gunpowder was best ignited in the center, the Fossano powder did not seem to suffer from ignition at the end of the charge.
Accident
During firing trials on 5 March 1880, one of Duilios guns cracked while firing at the maximum charge. At the suggestion of the British Army, it was officially established that the maximum practical charge was and not .
British Service
British response