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100 Ton Gun in Gibraltar

By Nick Nutter | 24 Jan 2018

In the early 1870s the French built a 420mm (16.5ins) 76 tonne gun for their naval forces. This exceeded the largest gun in the Royal Navy’s arsenal a 320mm (12.75ins) 38.6 ton (39,219kg) gun. This was unacceptable and the Royal Navy asked for an 81 ton (82,299kg) gun.

In response Sir W.C.Armstrong at Newcastle Upon Tyne, owner of the Armstrong Whitworth manufacturing company and its armaments division the Elswick Ordnance Company, commenced a project to build a 100 ton (101,604kg) gun. He believed that in the time it took to design and build such massive guns other countries, particularly France, would build an even larger gun. He hoped to leapfrog ahead with a gun so large that it would take many years for other engineers to develop a better and larger design. At first this was rejected by the Royal Navy as too heavy and too expensive.

Armstrong was not deterred and eventually went on to build 12 guns in total to his new design. The first eight were sold to the Italian Navy in 1874 to arm their new battleships, Duilio and Dandolo. This immediately gave them superior fire power over the Royal Navy’s HMS Inflexible which was being built in 1874 and more worryingly, would allow the Italian ships to bombard Malta whilst staying out  of range of the 12.6ins (320mm) guns on that island. Since 1869 Malta had become a key strategic position in the Mediterranean following the opening of the Suez Canal. This was of concern to the Royal Navy because Francesco Crispi, an Italian statesman ranked at the time with Bismarck, Gladstone and Salisbury and a driving force in the Italian reunification of 1871 had called Malta ‘Italia irredenta’, ‘Unredeemed Italy’, in other words he considered Malta should be part of the now unified Italy.

The Royal Navy responded by asking British arms manufacturers for a gun capable of penetrating 36ins (91.44cm) of steel at 1000 yards (914.4 meters). Designs were tendered for guns weighing 163, 193 and 224 tons (165.615, 196,097 and 227,594 kilograms). Apart from the enormous expense, the time it would take to bring them into service would be many years. In 1877 the problem was considered crucial. Duilio was undergoing sea trials. The chief of Malta’s defences, Simmons, was called to London for consultation. He asked for four guns identical to those on the Duilo and Dandolo, reckoning that a shore battery was more stable and could achieve more accuracy and range, if situated at a high elevation, than guns mounted on naval ships. It was decided to use Armstrong’s design, that being the fastest, simplest and least expensive option. Armstrong’s decision was vindicated.

Meanwhile Gibraltar, equally strategically positioned controlling the entrance to the Mediterranean and hence all shipping that had left the Suez Canal bound for the Atlantic and shipping intending to use the canal bound for the Far East, asked for some big guns as well. Malta lost two of its weapons to Gibraltar.


Construction of the Gibraltar guns started in 1878. The first was delivered in December 1882 and was ready in July 1883 and the second was delivered in March 1883 and mounted by September the same year.

First firings took place in 1884 but, due to problems with the hydraulic systems, the guns were not fully operational until 1889.

One gun was placed at Victoria Battery, now the site of the Fire Station, the second at the better strategic position of Napier Magdala battery covering Rosia Bay. The gun now at Napier is actually the gun from Victoria, the original having split its barrel during a test firing. The overenthusiastic gunners had managed to achieve a firing every 2.5 minutes, far in excess of its designed one shot every 4 minutes. One can only imagine the angst of the civilian engineers from Elswicks’ as they saw their beloved gun so mistreated.

It is only when you stand on the battery next to the gun that its size is fully realised. Visitors will notice that in addition to two hydraulic pistons at the back of the platform designed to absorb the energy of the recoil, the gun platform is also sloped, the angle is actually 4 degrees. This design feature was to further lessen the recoil length which was 5.75 feet (175.26cm).


Each weighed 100.2 tons (101,807kg) and had a barrel 32.65 feet (995.17cm) long and a bore of 17.72ins (45cms). Of that length 30.25 feet (922cm) was rifled which greatly increased the accuracy of the gun. Guns of this design were called RMLs, Rifled Muzzle Loaders. The shot fired weighed 2000lbs (907kg) and the charge was 450lbs (204kg) of black prism gunpowder. This gave a muzzle velocity of 1,540 feet per second, (46,939cm per second) which is just over 1,000 miles per hour (1609kph), well in excess of the speed of sound and a range of 8 miles (12.87km). When it reached its target the shell could penetrate 24.9ins (63.25cm) of iron. The gun could fire one round every four minutes and required 35 men to serve it, 18 of whom were required to handle the ammunition.

To cope with the massive weights involved in loading and traversing, each gun had a steam engine that fed high-pressure steam to a hydraulic accumulator. It took 3 hours to generate the required head of steam. Not surprisingly the gun at Gibraltar was nicknamed ‘The Rockbuster’. They were the largest muzzle loading guns ever built but were soon obsolete due to the introduction of breech loading systems. The main benefits of a breech loading system are that the gunners are protected behind the gun shield and fortifications whilst they are reloading and a faster load time.

The gun was fitted with an optical system for aiming and firing could be either mechanical or in later years electrical. In the early days of service Depression Range Finders were mounted on each flank of the gun. Instructions to the gun layers were transmitted by megaphone. This system had the disadvantage of requiring visual sight of the target, not always possible on Gibraltar due to sea mists and the Levanter cloud that often obscured the Rock. After firing, the smoke from the discharge also had a habit of obscuring the view. The Position Finder, developed after the DRF, could calculate both range and bearing. With the advent of electricity the systems were adapted so that the DRF and PF could be situated high on the Rock and connected to the gun batteries by cable. There dials displayed the elevation and bearing information as calculated by the DRF and PF. This information was called out to the gun layers who then aimed the gun. The information was updated regularly so that the gun ‘tracked’ the target. Firing was initiated electronically by the Battery Commander high up in his Command Post who would then observe where the shot fell and make adjustments accordingly.

Shells could be one of three types. The armour piercing shell was 44ins (112cm) long and contained a 32 pound (14.5kg) explosive charge. It could penetrate 21ins (53.34cm) of steel at 2,000 yards (1828.8kms). The high explosive shell was 48.5ins (123.19cm) long with an internal 78 pound (35.38kg) charge whilst the shrapnel shell was 45ins (114.3cm) long and contained a 5 pound (2.3kg) charge and 920 bullets each of which weighed 4 ounces (11gm).

Firing charges were polygonal in shape, 15.71ins (40cm) wide and 14.5ins (36.8cm) long and each contained 1cwt (50.8kg) of ‘Large Black Prism’ propellant. Four or five charges were used to achieve maximum range.

Beneath the battery a system of passageways led to magazines that could hold 87 shells and 107 charges. A mini railway transported the shells to the twin pneumatic hoists which were used to load the guns as well as elevate and rotate the guns on their mountings.

In Operation

The 100 ton guns never fired a shot in anger. Installed in 1883, by 1888 they were effectively obsolete as muzzle loading guns were replaced by breech loaders. In that year Generals William Howley Goodenough and the governor, Sir Lothian Nicholson recommended reducing and standardising the guns on Gibraltar to make them easier to maintain and supply. There also initiated a move to locate heavy guns higher up the rock where they had better visibility and greater range.


In 1902 the Inspector General of Artillery visited the battery to see the gun fired. Unfortunately only the tube, the small charge used to fire the main charge, exploded. The misfire drill was carried out to no avail. The only option left was to draw the shot. After waiting thirty minutes, just in case the main charge did fire, the call went out for volunteers to be lowered down the barrel to fasten the shell extractor to the nose of the shell some 25 feet inside. A small, thin gunner was volunteered and duly lowered into the barrel. He successfully attached the extractor and both he and the shell were safely removed. He was immediately promoted to the rank of bombardier.

Last Firing

The last symbolic firing of the ‘Rockbuster’ took place in 2002 to mark the Calpe 2002 Conference between Gibraltar and Malta. Today visitors to the interpretation centre and the gun marvel at this monument to Victorian steel and steam engineering from an era when Britain really did Rule the Waves.

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