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Rockbuster - 100 Ton Gun

Rockbuster - 100 Ton Guns placed at Gibraltar. They were the largest muzzle loading guns ever built, never fired a shot in anger and were obsolete within 5 years

By Nick Nutter | Updated 12 Jun 2023 | Gibraltar | Places To Go | Login to add to YOUR Favourites Favourites Icon or Read Later

This article has been visited 35,138 times 100 Ton Gun Gibraltar 100 Ton Gun Gibraltar

100 Ton Gun Gibraltar

On the 10th December 1882, the Steamship Stanley, five days out of Falmouth, arrived at the New Mole in Gibraltar. On board was the gun barrel of a 100 ton, rifled, muzzle loading gun, the largest RML gun in the world. Captain English of the Royal Engineers had the task of mounting the barrel at Napier of Magdala Battery about 400 yards from the Mole.

Arms Race between Britain, Germany, France and Italy

100 Ton Gun Gibraltar 100 Ton Gun Gibraltar

100 Ton Gun Gibraltar

The operation did not go well from the start. English had equipped himself with a specially built set of iron sheer legs with which he intended to lift the barrel off the ship and place it on a purpose-built sleigh alongside. Sixty men manned the capstan, round which was the wire that ran to the top of the sheer legs and from there to the trunnions on the barrel to which it was fixed. As the men turned the capstan, the barrel lifted from the deck of the Stanley. As the enormous weight was raised the Stanley lifted with it making it impossible to swing the gun outboard. Undeterred, Captain English filled the holds with 100 tons of sand, rocks, soldiers and water. Onlookers were treated to the unusual sight of the ship sinking beneath the gun that could then be swung over and lowered onto the sleigh. It took a further twenty-one days to drag the sleigh to the battery. To put the weight into perspective. The space shuttle Endeavour weighs 78 tons and can carry a payload of a further 22 tons making its total all up weight 100 tons.

The need for such a massive weapon was a consequence of the arms race between Britain, Germany, France and Italy. Each was trying to surpass the other regarding the size, speed and power of capital ships and armaments. The development of increasingly powerful weaponry tended to keep pace with the development of the defences they were designed to breach. From the middle of the 19th-century, iron-built ships were increasingly common in the fleets of the major powers in Europe. Cannon, basically unchanged since the 14th century, were not powerful enough to fire cannonballs that would penetrate the hulls of this new breed of ship. Only 100 years earlier the largest guns mounted on the Kings Bastion during the Great Siege (1789 – 1783) fired a round shot weighing 34 lbs and had an effective range of about 1,000 yards.

In the 1870’s France and Germany were edging in front of Britain in the race. The French built a 16.5ins, 76-ton gun for their naval forces in the early part of that decade. Then the German manufacturer Krupp started to make similar sized guns for the Turkish navy. Both were superior to the largest gun in the Royal Navy’s arsenal a 12.75ins, 38.6 ton, gun. The situation was unacceptable to the United Kingdom, and the Royal Navy asked the government to commission for an 81 ton gun.

In response, Sir W.C.Armstrong at Newcastle Upon Tyne, the owner of the Armstrong Whitworth manufacturing company and its armaments division the Elswick Ordnance Company, commenced a project to build a 100 ton gun. He believed that in the time it took to design and build such a massive gun, 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. The Royal Navy rejected the 100 ton gun as too heavy and too expensive.

Armstrong was not deterred, especially when, in 1874, the Italians commissioned twelve of his new design. They were to be fitted to three new battleships of the Duilio class. It would make them the most powerful ships in the world. As it transpired the Italians could only afford to build two of these monster ships, the Duilio launched in 1876, and Dandolo, launched in 1878.

The new guns immediately gave the Italian Navy superior firepower 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 guns on that island. Following the opening of the Suez Canal in 1869, Malta had occupied a key strategic position in the Mediterranean. The new Italian guns were 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 that Malta should be part of the now unified Italy.

The situation at Malta highlighted a problem all the naval powers had. Warships are at their most vulnerable when in harbour restocking on fuel, coal in those days, food, water and ammunition. It is therefore essential that the harbours are well protected. The Royal Navy responded to the potential Italian threat by asking British arms manufacturers for a gun capable of penetrating 36ins of steel at 1000 yards. Manufacturers submitted designs for guns weighing 163, 193 and 224 tons. 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.

Royal Commission

100 Ton Gun Gibraltar 100 Ton Gun Gibraltar

100 Ton Gun Gibraltar

In October 1877 General John Lintorn Arabin Simmons was invited to join a Royal Commission appointed to inquire into the condition and sufficiency of the means provided for the defence of the more important seaports within the Colonial Possessions.

After considering the defences at Malta, he asked for four guns identical to those on the Duilo and Dandolo, calculating that a shore battery was more stable and could achieve more accuracy and range when situated at a high elevation than guns mounted on naval ships. It was decided to use the four surplus guns that Armstrong had designed and built for the Italians, that being the fastest, simplest and least expensive option. (In 1884 Simmons was appointed Governor of Malta.)

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.

Delivery of the 100 Ton Guns

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.

One gun was placed at Victoria Battery, now the site of the Fire Station, the second at Napier Magdala battery covering Rosia Bay, strategically a better location.

First Firing of the 100 Ton Gun

First firings took place in 1884 but, due to problems with the hydraulic systems, the guns were not fully operational until 1889. The gun now at Napier is 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 more than 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.

Visitors to the 100 ton gun exhibition at Napier of Magdala Battery 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 sloped at an angle of 4 degrees. This design feature was to lessen further the recoil length which was 5.75 feet.


Each gun weighed 100.2 tons and had a barrel 32.65 feet long and a bore of 17.72ins. Of that length, 30.25 feet 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, and the charge was 450lbs of black prism gunpowder. The combination gave a muzzle velocity of 1,540 feet per second, which is just over 1,000 miles per hour, much faster than the speed of sound, and a range of 8 miles. When it reached its target the shell could penetrate 24.9ins 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. Each gun, to cope with the massive weights involved in loading and traversing, 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 while they are reloading, and they achieve a faster load time.

Optical Firing System

The gun was fitted with an optical system for aiming. 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 locally named Levante 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. On the gun platform, 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. The 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 long and contained a 32-pound explosive charge. It could penetrate 21ins of steel at 2,000 yards. The high explosive shell was 48.5ins long with an internal 78-pound charge while the shrapnel shell was 45ins long and contained a 5-pound charge and 920 bullets each of which weighed 4 ounces. Firing charges were polygonal in shape, 15.71ins wide and 14.5ins long and each contained 1cwt 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.

Obsolete after 5 years

The 100-ton guns never fired a shot in anger. Installed in 1883, by 1888 they were effectively obsolete as breech loaders replaced the muzzle-loading guns. 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.

100 Ton Gun misfires

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.

A story, probably apocryphal, started circulation soon after this event. 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 removed safely. The gunner was immediately promoted to the rank of Bombardier.

Since withdrawing a shell from the barrel was not an uncommon requirement a mechanical shell extractor had been invented years earlier. It was kept in the Battery Stores.

Last symbolic 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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