A Brief History of the Paris Guns
by Roger Todd

Paris Kanone 1 Without doubt among the most extraordinary pieces of artillery ever devised, the Paris Guns have long fascinated military historians and aficionados of the bizarre alike. They are as shrouded in mystery as the "super guns" the misguided artillery genius Gerald Bull designed and built for Saddam Hussein. Perhaps aptly, it is thanks to the late Dr Bull that many of the mysteries of the Paris Guns have been resolved. Much of the information in this article is based upon his collaborative book with Dr Charles Murphy, "Paris Kanonen – the Paris Guns (Wilhelmgeschutze) and Project HARP", in which Bull analysed past writings and used his formidable knowledge of gun design to great effect. Bull was also fortunate to have in his possession the unpublished papers of the Paris Guns’ chief designer, Prof Fritz Rausenberger.

Known by the Germans also as Wilhelmgeschütze (William’s Gun, after the Kaiser, but emphatically not Big Bertha), the operational history of the Paris Guns has been described in a variety of publications. There are, however, many aspects of the technical development and construction of the guns which have been glossed over, leading to the perpetuation of many myths, minor though they may be. Thus, although not claiming to be in any way definitive, this article will concentrate on the technology of the guns, with, perhaps, one or two surprises thrown in.

Prior developments in long range gunnery

For centuries, artillery ranges had barely increased beyond a few kilometres as crude, cast smoothbore muzzle-loading cannons used black powder to fire round shot (or grape). But the advent of the chemical and metallurgical industries in the nineteenth century, leading to new smokeless powders vastly more powerful than black powder and "built up" rifled cannons consisting of "hoops", or tubes, of iron (and, later, steel) shrunk over each other to produce much stronger stressed barrels, enabled far greater ranges to be achieved. Equally crucial to these developments was the advent of breech-loading, enabling a much longer barrel to be used.

The greatest impetus to the development of large guns was naval technology. Only battleships were large enough to provide mobile platforms for these guns, with land warfare mainly utilising light field pieces, with large, relatively short-range, guns only employed in sieges. Yet for some time, even naval tacticians only envisaged short ranges with battles being fought at close quarters, the huge size of the guns necessitated by the need to pierce ever thicker armour plate. It was the advent of efficient locomotive torpedoes that drove the increase in gunnery ranges at sea, which in turn led to the development of technological solutions for range-taking and sighting, and also resulted in the all-big-gun battleship, or "dreadnought".

Without doubt, the master gun makers in Europe, and thus the world, were Krupp of Essen. Already in 1914 they had astonished the world with the infamous Big Bertha, the 42cm Type M mortar. This monster siege gun was the brainchild of Prof Fritz Rausenberger, and was a light-weight, mobile version of the 42cm Gamma mortar, itself a development of coastal defence artillery. Firing at high angles, the plunging shells from such guns would easily penetrate the weakly armoured decks of approaching enemy battleships, something the Japanese had proven to devastating effect at Port Arthur in 1904. As the Great War dragged on and settled into the siege-like conditions of trench warfare, the German Army started to use large, long range guns to shell far behind enemy lines. And as the only guns capable of such work were naval, several 38cm barrels meant for superdreadnoughts ended up being mounted on land carriages, manned by sailors from the High Seas Fleet! Freed from the restrictions of turrets which limited elevation to 20 or 30 degrees, these guns, the Lange Max, could fulfil their potential, especially when equipped with the new, slender capped shells Krupp were developing.

The use of these guns had evolved from a German Naval Board request in 1914, when it appeared that German forces would sweep to the French coast, for a gun capable of shelling Dover from Calais. Experiments by Krupp with a 52.5 calibre (L52.5) 35.5cm gun achieved ranges of 49km, far exceeding the Navy request for 37km. Later, when the dash for the Channel had ground to a halt, the Army appropriated the 38cm barrels for use at Dunkerque, Nancy and Verdun.

These experiments uncovered what appeared at first sight to be a strange result: that maximum ranges are best achieved at elevations of around 50 to 55 degrees, not the 45 degrees that geometry (and ideal conditions in a vacuum) would suggest. The reason, Krupp’s technicians quickly appreciated, was that the earth’s atmosphere grows thinner the higher the altitude. Consequently, at the higher elevations, a long-range shell is travelling for a greater part of its trajectory through very thin air, increasing the range. This phenomenon would be significant for the Paris Gun project.

Genesis of the Paris Gun

Paris Kanone 2

It was Prof Rausenberger who, as Krupp’s technical manager, proposed to the German High Command an ultra-long range 100 km system firing 21cm 100kg shells. Employing his friend Col Bauer, an Army High Command section chief, as intermediary, Generals Hindenburg and Ludendorff were approached. Their approval was immediate, and Rausenberger set his team to work. With a development time laid down of only fourteen months, and conventional artillery systems (never mind one such as this!) taking at least five years to develop, Rausenberger had to devise a novel solution. Dr Otto von Eberhard, Rausenberger’s assistant and technical director of the project, however, proposed a method that was too radical even for Rausenberger. This he rejected, and it will be discussed later in this article.

First, Rausenberger determined that to achieve the desired range, an unprecedented muzzle velocity of 1500m/s was required (the experimental 49km range gun had a muzzle velocity of 940m/s). This, it appeared, could only be achieved with a very long barrel. To expedite matters, Rausenberger proposed using 35cm naval guns intended for the "Ersatz Freya" (a "Mackensen" class battlecruiser), construction of which had been suspended in autumn 1916 after the lessons of Jutland had sunk in. There were nine of these barrels, and they had not yet received their rifled sleeves. Instead, they would have a 21m long 21cm calibre rifled liner inserted, and the chamber would be modified to accept the standard naval 28cm cartridge case. In order to permit rapid turnaround when replacing worn liners, they would be rebored first to 224mm, then 238mm. And if the Navy decided to complete the battlecruisers (which, in the end, they never did), the barrels could be easily converted back to their original form. Later, a few 38cm gun barrels were also pressed in to service.

At this point, with development still in its early stages, the German High Command suddenly in early 1917 requested a 20km increase in range (due to a planned withdrawal of the front line). Rausenberger’s team had to perform the calculations all over again, increasing muzzle velocity to 1610m/s to achieve the now incredible range of 120km.

Paris Kanone 3
A new problem presented itself. To achieve the necessary muzzle velocity, an in-bore shot travel length of at least 24m was required, but Krupp’s largest rifling machine could only handle 18m. Rausenberger then decided to extend the rifled barrel with a smoothbore tube, which would be bolted on to a flange attached to the muzzle. There were, in fact, three lengths of extension tube, depending on the maximum range desired: a 3m tube; 6m; and 12m. The resulting barrel measured overall up to 34m in length: one metre of breech-ring assembly behind the barrel proper; a 3m chamber; the 18m rifled section; and a maximum 12m smoothbore extension.

Another problem was barrel droop, from which, to an extent, many long heavy guns suffered. British heavy naval guns, which were "wire-wound" rather than using shrunk-on tubes, were especially prone to droop, but would straighten out momentarily upon firing, and accuracy was not affected. But the Paris Guns’ extraordinarily long and slender barrels would droop badly under their own weight, by perhaps as much as 9cm at the muzzle. Hence the distinctive, suspension-bridge-like truss which was equipped with screw-jacks to apply tension to the barrel and straighten it out, after taking sightings with a temporary breech-mounted telescope and a frosted glass disc with central cross-hairs fitted in the muzzle.

Paris Kanone 4


Paris Kanone 5
It has already been mentioned that the Paris Guns needed smoothbore extensions to the rifled barrels. This presented a dramatic problem: how to seal the barrel behind the shell when the projectile moved from the rifled to the smoothbore section. Conventional shells of the period had copper driving bands around the base. When rammed hard into the chamber of a gun barrel, the steel "lands" (the raised areas between the rifling grooves) bit into the relatively soft copper, so that when fired, as well as following the rifling to impart spin to the shell, the copper also expanded under pressure to fit the grooves and create a seal. But in moving from the rifled to the smoothbore section of a Paris Gun, a conventional shell would allow propellant gases to rush through the gaps between the raised lands of the driving band, causing a drop in pressure (and thus muzzle velocity) and setting up turbulence ahead of the shell, causing instability as the projectile left the muzzle.

In any case, conventional copper driving bands could not be used. The enormous pressures and velocities inside the barrel would strip the copper off, leading to the first step of Rausenberger’s solution: pre-machined grooves cut into raised "waistbands" cast integral with the steel shell bodies themselves, forming ribs which fitted the barrel rifling precisely. But this still did not resolve the rifled-to-smoothbore transition.

Paris Kanone 6
Months of experiments with dozens of different shell designs were carried out to produce a solution under-appreciated to this day. In their final form, the shells were cast with two sets of rifling ribs, one towards the front of the main body (that is, minus the pointed aerodynamic cap) and another towards the rear. Then, behind each set of rifling ribs, a series of small ribs were machined at right angles to the longitudinal axis, going all the way around the shell body. Onto these were fitted copper bands with pre-machined rifling ribs on the outside, and grooves on the inside which engaged with the raised ribs in such a way that the copper band could rotate only so far as to allow the raised areas (or "lands") to block the hollows between the corresponding lands cut into the steel shell body in front. The ribs on the steel shell were strong enough to withstand the stresses of firing and impart the requisite spin, while the copper bands still functioned as they did on conventional shells by expanding and sealing (or obturating) the barrel.

Paris Kanone 7
As the shell moves from the rifled to smoothbore section, the forward copper band, through friction with the barrel wall, fails to rotate as fast as the rest of the shell, thus moving a fraction in the opposite direction to the shell proper and blocking the hollows between the lands of the shell body in front, forming an obturating seal. As the rear part of the shell passes the transition point, propellant gasses leak past before the copper band has had time to fully rotate in its turn, but as the front band has already formed a seal, any gas leakage ahead of the projectile is prevented.

This dual rotating band configuration was only achieved after much trial and error. Earlier shells had a single rotating band, leading to gas leakage and in-barrel "torching" as gases leaked past the band during the fraction of a second it took to rotate and close the gaps.

Barrel wear

With the system operating at such high pressures and temperatures compared with conventional guns, barrel wear was expected to be considerable. An unmodified naval gun could fire up to 800 rounds before wear affected accuracy. The Paris Guns wore out after around 60 to 70 rounds, at which point they went back to the Krupp works to be bored out and have larger calibre replacement liners fitted (range was reduced by around 25km). Each time the gun was fired, the front of the chamber advanced forward around seven centimetres, and around an extra ten kilograms of propellant were needed to maintain range. The calibre of the gun also increased fractionally with each round fired, so that successive shells had wider driving bands to seat them.

Mountings and carriages

Paris Kanone 8

In photographs of the Paris Guns, it can be seen that there were two types of gun carriage employed. For the tests in Germany, a box-like coastal-emplacement carriage was used, with a turntable at the front, allowing limited traverse on wheels along a circular arc of rail at the rear. Operational guns used the railway type mounting as seen on the Long Max, which were lowered onto, and then bolted to, a circular turntable on a concrete emplacement [figure: artist impression of operational mounting]. This allowed full traverse. However, one intriguing photograph shows what appears to be an operational gun in a forest on a naval type mounting.

Paris Kanone 9 Paris Kanone 10

The carriages were, as far as can be ascertained, hardly modified. All operations, such as traversing the carriage and depressing and elevating the barrel were done by hand, dozens of men operating windlasses and like mechanisms. The barrels themselves had to have large counterweights of iron ballast bolted above the breech to balance the whole assembly about the trunnions. Despite the much larger propellant charges used, the light weight of the shell meant that recoil was actually less than on 38cm guns, and the sound and shockwave on the ground considerably reduced, owing to the muzzle being so much farther away.

Planned developments

In his papers, Rausenberger states that more 38cm barrels were to have been converted which would have allowed two guns to shell Paris continuously for a year. His team was also planning to fit a 15m smoothbore extension and use reduced drag shells which would have extended the range to 142km, which, as Rausenberger states, "would have been sufficient to bombard London from Calais". Most ambitious of all, fully aware that the use of 21cm shells could only ever achieve psychological effects, in May 1918 the Krupp team was already designing a 30.5cm system firing 300kg shells to a range of 170km (105 miles). Of course, the armistice of November 1918 dashed any hopes of ever developing such a weapon.

Paris in ruins?

Paris Kanone 12
Finally, an intriguing detail emerges when reading Rausenberger’s own account of the early stages of the Paris Gun design process. Earlier, it was remarked that when Rausenberger was trying to decide how to achieve the requisite muzzle velocity, his assistant, Dr von Eberhard, had made a very radical proposal. Simply, von Eberhard speculated that if the unmodified L52.5 35.5cm gun, which fired a conventional shell of 535kgs, were to use a 90kg 21cm shell slotted into a 120kg 35.5cm calibre short cylindrical "carrier", the combination weighing 210kg, a muzzle velocity of 1500m/s was easily attainable. As the assembly left the muzzle of the barrel, aerodynamic drag on the flat-fronted cylinder would rapidly decelerate it, causing drag separation of the slender 21cm shell and allowing it to continue at the same velocity and reach 100km range.

Von Eberhard had essentially invented the sub-calibre discarding-sabot shell. Rausenberger’s objections to it appear odd, in retrospect. First, he decried the light weight of the shell, only 90kgs. Yet the Paris Gun as built fired shells weighing, on average, only around 100kgs. Further, because von Eberhard’s solution offered a gun firing the sabotted ammunition at normal barrel pressures, his 90kg shell could have relatively thin walls and contain around 18kgs of explosive, as opposed to the Paris Guns’ projectiles with their thick walls (to resist the enormous barrel pressures) and consequent light explosive payload of only around 7kgs. Even better, with the guns operating at normal pressures, barrel lives of 800 rounds could have been confidently expected, as opposed to the Paris Guns’ ephemeral barrel lives of around 65 rounds. More justifiably, perhaps, Rausenberger was also unsure about testing such a novel system in the short time available, and criticised the possibility of the discarded sabots falling on German troops.

Had von Eberhard’s solution been adopted, it can be seen quite easily that the effects of the bombardment would have been an order of magnitude greater. Unmodified naval guns could have been used, the sub-calibre sabotted ammunition system being the sole key to achieving ultra-long ranges. By rejecting von Eberhard’s idea, Rausenberger had inadvertently saved Paris from massively greater destruction than occurred.

What did the Paris Guns achieve?

Apart from the deaths of some 256 Parisians, and around 620 wounded, what did the guns actually achieve? What was their purpose? And in military terms, were they worth the immense effort that appears to have gone into them?

Rausenberger was under no illusions that the guns could only ever have been used for the bombardment of a city, not specific installations, given their inaccuracy, although even he dissembled at one point, writing that "the only possible use of such a 100km range gun would be the bombardment of the Paris fortifications, an area target some 20km in width and breadth" (emphasis added). With such a light weight explosive payload, the small number of shells that hit Paris did relatively little damage, apart from the "lucky hit" on the church of St Gervais, especially when compared with the bombings of the next world war.

The Germans appear to have seen the guns as a psychological, or terror, weapon. Combined with their big offensive on the Western front, they must have hoped to sap the morale of Parisians, disrupting business and government activities. On the whole, however, in this they appear to have failed, Parisians quickly getting used to the shelling, and only being really shaken after the St Gervais incident. The guns were also intended to demonstrate to the world the power of German science and technology, though whether such a tenuous aim really justified such a dramatic project is open to question. Certainly Rausenberger thought it was worth it, but as a technician, he probably relished the technical challenge as much as anything else.

On the other hand, did the effort that went into the development of the guns disrupt normal war production? It would appear not. Virtually all of the materials used were already in existence and surplus to requirements. No other project or normal war production was recorded to have been disrupted, and there is little reason, even in retrospect, to believe that this was the case.

Certainly, the guns were a technological tour de force. They had their genesis in the belief that the sheer shock value of such a novel weapon would in itself produce widespread fear and panic, albeit in combination with the Western front offensive. But given that this was at a time when the aerial bombing of cities far behind enemy lines was still in its infancy, the guns’ designers and sponsors can be forgiven for their excessive optimism in its potential effects. Ultimately, for all of their undeniable glamour, the guns were a failure as a strategic weapon. That role had to await the advent of the rocket during the next world war. - Roger Todd

Paris Gun Photo Gallery

Paris Kanone 13 Paris Kanone 14 Paris Kanone 15
Paris Kanone 16 Paris Kanone 17 Paris Kanone 18 Paris Kanone 19 Paris Kanone 26
Paris Kanone 20 Paris Kanone 21 Paris Kanone 22 Paris Kanone 23 Paris Kanone 24 Paris Kanone 25

The pictures below show a very nice model of the Paris Gun, shown in the impressive Technical Museum of the Bundeswehr in Koblenz. You will get additional info, and even inspiration, from these:

Paris Kanone 27 Paris Kanone 28 Paris Kanone 29 Paris Kanone 30 Paris Kanone 31

Additional Information

Do you want to know more? Then get hold of "The Paris Gun" by Henry W Miller. Admittedly, it is a bit dated, as it was published in 1930, but is good, even riveting reading on the operational history of the guns, and it contains a lot of maps and other illustrations. (This book was previously very rare and hard to get, but has recently been re-published in soft cover by The Naval & Miiltary Press Ltd.)