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This much important mission gave to this often small part of the ammunition one of the most important roles for the correct operation of all the giants, guns and projectiles, that are spoken about in the other pages of this website.
The fuzes that can still be found nowadays in the ploughings, embedded in earth or chalk and half destroyed, are remnants of precision mechanics and pyrotechnics systems... For a good understanding of the explanations and diagrams of the section 'WW1 fuzes', one might want to take some time to familiarize himself with some technical concepts of WW1 fuzes mechanics and pyrotechnics, one of the impressive examples of the creativity at the service of crime and horror...
Several types of fuzes were in use in 1914-1918. They can be roughly categorized on the basis of the timing needed for triggering the shell explosive charge :
'Percussion fuzes' were triggered by the impact shock at the arrival on the target, causing the explosion of the shell main charge.
'Delayed percussion fuzes' were percussion fuzes whose triggering at the impact was delayed by some fractions of a second, causing the explosion of the shell main charge after some penetration in the ground or target.
'Super quick (or instant effect) percussion fuzes' were percussion fuzes whose triggering at the impact was made as quick as possible before any penetration in the ground or target.
'Time fuzes' were triggered at a precise point of the projectile trajectory, by the ways of a pyrotechnic or clockwork time countdown system.
'Double effect fuzes' also named 'Time and percussion fuzes' combined the time fuze and percussion fuze behaviors, allowing to chose one or the other, and to ensure explosion at the impact if it happened before the end of the countdown or if this latter was defective. More generally, double effect fuzes could be the name of percussion fuzes with selectable optional delay.
'Multiple effects fuzes' were made by combining more than two different behaviors, including for instance in the same fuze a short delay, a long delay and a time system. The use of 'universal shells' at the beginning of the war gave way to very complex multiple effects fuzes.
These parts of the artillery ammunitions, designed to trigger the burst at a precise part of the shell trajectory or at impact despite severe conditions before the shell was fired (humidity, shocks, corrosion, ...) and during its shooting (huge accelerations and decelerations, high heat, rapid spin, violent shocks) were high precision mechanisms.
Of course, a fuze was also supposed to present all the safety guarantees for the gun crews : it had to be designed in order to sustain uncareful handling during transportation, uncontrolled storage conditions, and the violent acceleration of the shooting start in the tube without causing premature explosions, likely to destroy guns and crews... This additionnal specification added to the fuzes design complexity.
It is interesting to note that the trend of the pre-war was to develop more and more sophisticated fuzes, while the war experience, new types of shells and artillery techniques, and war economics induced at the contrary the use or more and more simple fuzes.
The embarked explosive charge of the fuze could be strong enough to trigger the explosion of the main charge of the projectile when filled with gun powder, but with the very powerful modern and more stable chemicals for high explosive shells (for example molten TNT or mélinite main charges), the fuze charge was only igniting a 'detonator' (also called 'intermediate charge' or 'primer') that had sufficient explosive energy to cause the shell detonation.
In these cases, French technology most often used to add a small separate primer at the base of the fuzes, and a bigger intermediate detonator inserted into the shell head.
Germans army engineers more often designed 'Detonators-fuzes' where the fuze body could be assembled (or was factory preassembled), with a large primer in a single part (often equipped with safety systems) before its mounting on the shell body.
French 24/31 Typical french high explosive shell pyrotechnic line : from the left to the right, the fuze itself, the adaptator screw ring, the small primer usually screwed on the fuze tail, and the bigger intermediate detonator often mounted into the shell body | |
German Dopp Z 96 fuze assembled on a HE shell, showing the primer attached to the tail before mounting on the shell top gaine |
The mecanics science principle of inertia was widely used in the WW1 fuzes design.
This pnenomenon is the same than the one that projects forward non immobilized objects in a car braking suddenly, or backwards when the same car accelerates violently, and is modelized by the famous Newton formula 'F = M x a'. It was equally applicable to any free moving object inside a fuze body attached to a shell violently accelerating in the gun tube at the departure, or decelerating even more violently when hitting its target.
Associated with a pyrotechnic igniter that needed the penetration of a hard pin (named 'percussion pin', see an example at left) into a cap filled with a flammable solid (most of the time mercury fulminate, named 'percussion cap'), it allowed a pyrotrchnic activation under the effect of an acceleration or a shock.
The way the fuzes inertia mecanisms worked was most often comparable to the one exposed in the scheme at right :
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In this last case, the apparatus was turned upside down so that the mobile graze pellet was moving backwards.
Fuzes were (and still are...) dangerous pieces of equipment, designed to create a flame, an explosion or even a detonation on a shock or when ignited. Safety devices were necessary to ensure they would not act this way elsewhere than in enemy territory, just when they were wanted to do so. Springs and pins : the basic arming devices Stirrups and ramps : inertia arming systems : Pyrotechnic arming system Centrifugal force arming system The centrifugal force effects were used in numerous fuzes or detonators safety devices, as shown in the following examples :
Uncareful handling during transportation, accidental falls during manipulation, surrounding enemy shelling shockwaves were only examples of so many things that could frequently happen to the fuzes in an usual war environment before their use. Military engineers had to invent safety devices that would inert the fuzes before they were assembled to the shell and shot by the gun.
But another danger existed within the gun itself at the very first instants of the fuze active life : the brutal acceleration of the departure could also cause premature triggering of the fuze and shell explosions still in the barrel, often destroying both the material and its servants... This was another reason for designing safety and arming techniques that would avoid such catastrophies.
Removing the safeties of a fuze is called 'arming'. This could be done manually while the fuze was still attainable, but had to be done automatically from the time it disappeared into the gun breech hole. The corresponding devices are many, and the following list is just intended to give an idea of their varieties, using pins, springs, centrifugal force or pyrotechnics.
French fuzes often included an auto-arming device, designed to remove a mechanical safety under the action of the shock of departure. This additional safety gave more guarantees than the basic safety spring that was then just kept for providing the in-flight safety, and allowed to avoid safety pins that could be dangerous if accidently removed in the heat of the moment, and were detrimental to the rate of fire since it added an additional operation from the firing crew.
These inertia auto-arming systems all had the same goal of keeping the graze pellet and the percussion pin out of reach of each other before the shot.
French most famous ones were named 'Robin' system and 'Peuch' systems.
The Robin system has been widely used in French fuzes. One classical example is be the 24/31 Mle 1899/08 fuze
The wartime scheme at far left shows that fuze, using a Robin arming system for the percussion system in the tail and another kind of stirrup system in the top head mechanism ('Lejay' type) for an additional safety. The picture at left shows the remains of such a fuze that can be easily comparred with the scheme.
This mechanism was also used in other fuzes, including the time and percussion fuze 30/38 Mod 1884 and its numerous followers.
Below, a dismantled Budin fuze, ancestor of the Robin system, showing the percussion pin, the safety spring, and the starter-bearer equipped with a staple mechanism that had to be compressed by the departure shock energy in order to enter inside the inertia block.
Helicoïdal ramps ('Peuch') system
Another classical French auto-arming system was the helicoïdal ramps type invented by M. Peuch. In this system first implemented in 1914 in the fuze 24/31 Mle 1914, and later in the mine-throwers fuze 24/31 Mod 1916, the accidental meeting of the percussion pin and the detonator cap was prevented by an intermediate cylinder that could shorten itself thanks to an ingenieus system of helicoïdal ramps.
An alternative to the French inertia arming system was introduced by the German military engineers with the pyrotechnic safety. These devices were based on a blocking stem and gunpowder grain system.
This system was widely used in German percussion fuzes as well as in time fuzes. Its advantage was that it allowed to arm the fuze only after the full combustion of the compressed gunpowder grain, that is somewhere on the shell trajectory after leaving the gun barrel. On the other hand, combustion gasses needed some more machining in the fuze for the fumes vents and the necessary igniting system, adding to manufacturing complexity.
Wartime scheme of the KZ14 German percussion fuze, using the pyrotechnic safety system. One can see the system housed on the top of the fuze in two cylinders, one with the concutor, the other one with the compressed gunpowder grain and the stem, as well as the fume vent.
Section of the same fuze, showing the same mechanisms damaged by the explosion.
A completely different pyrotechnic safety system was integrated inside the medium and large minenwerfer fuze ZsumMW. In these devices, the combustion of compressed gunpowder grains ignited at shot departure was needed to allow the action of springs opening metallic jaws that were blocking the movements of the main percussion system at rest.
Another classical way of arming fuzes after the departure of the gun was to take the opportunity of the spin movement of the shell when fired with a rifle bore tube. This rapid movement gave way to very high centrifugal forces in the shell and fuze.
That effect was mainly used by German fuzes and some British or French ones. One of the specificities of such a phenomenon was that the centrifugal force remains applied to the shell during the whole trajectory, while the inertia needed for stirrup mechanisms was only available during the acceleration par of the trajectory, that is inside the gun barrel.
The centrifugal effect gave way to various systems, and was also used for detonator safety systems.
Traditional centrifugal safety system (with a single side stop) of the percussion system of the German HZ14 Fliehb. fuze
Centrifugal detonator safety of the German KZ11Gr fuze, with a sliding block interrupring the pyrotechnic line between the fuze and the detonator, moved away by the action of cenrifugal force created by the shell spin, and blocked at rest and while in the gun barrel by a pyrotechnic safety.
Centrifugal detonator safety of a HZ16 German fuze, evolution of the precedent KZ11. This safety was generalized to many German fuzes post 1916
Percussion fuzes were designed to trigger the burst of the shell when hitting the ground, an obstacle or the aimed target. Originally dedicated to siege guns and projectiles, they became more and more used during the war with all guns including the fieldguns, with the progressive replacement of the classical shrapnell shell for anti-personnal missions by HE shells, inspired by the trench war experience.
Depending on the type of target to be destroyed, it could be necessary to fine tune the precise moment of the explosion in relation with the moment the shell body itself would impact the target.
Yet at the beginning of the war, HE shells fuzes could be equipped with delay systems that would trigger the shell burst some hundredth or tenths of a second after the impact, allowing the shell to perforate a protective coating of concrete, wood or shielding before exploding. During the war, this kind of behavior proved very useful against trenches, deep dug-outs, tanks, or even to create large craters, or to let gaz shells liberate their poison slowly from the ground.
The war experience also induced the fighting armies from each side to feel the need for a percussion fuze that would act so quickly that it would trigger the explosion of the shell before the warhead really entered into the ground or the target. This is how superquick fuzes were invented and mounted on HE shells for anti-personnal, barbed wires destruction or gaz spreading missions.
Non delayed percussion fuzes
Delayed percussion fuzes
Classical direct action fuzes could prove inefficient when hitting a steel shield or a reinforced concrete surface. In both cases, the shell would burst before it could penetrate into the hard surface, and the shield would be left almost intact. Delaying the fuze action for less then a tenth of a second would let the shell enough time to pierce the shielding and explode behind it or into it, with much more damages. This result could be obtained by inserting a delay (a tiny compressed gunpowder grain) in the classical pyrotechnic line of a percussion fuze, between the graze pellet inertia system and the detonator. This kind of fuze was also found pretty useful with some kinds of gaz shells when the desired effect was that the projectiles digs himself into the ground and slowly liberates its poison for a zone interdiction, against fortresses with perforation shells (with specific fuzes inserted into the shell base to avoid their premature destruction on the concrete), or against tanks. |
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Zoom on the pyrotechnic line of a French 24/31 Mle 94/08 percussion fuze including a small 0.05 sec delay just before the detonator. |
Whereas French and British fuzes were most of the time originally built with or withour delay, or could be quickly adapted by inserting a delay into the tail, the German engineers wanted to create polyvalent fuzes with selectable delays. This behavior was obtained either by the use of :
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Wartime scheme of a theoretical selectable separate pecussion systems | Wartime scheme of the BdZ10 base fuze delay selection system, based on a single percussion system whose flame could be directed to different channels delayed or not, by the means of an external selector screw. |
Operation of the selectable separate percussion systems type :
This kind of selectable delay systems gave way to very complex material, as it can be seen on this German percussion fuze with optional delay GrZ04. The left picture shows the inner scheme with the two separate percussion systems, while the right one is a tail view of the same fuze showing the complex inner organization with the holes of the two percussion systems and different safety systems. This complexity was a real handicap in wartime economy, and the new fuzes designed during war were much simplified. |
Super-quick percussion fuzes
The basics of such a 'push-back fuze' (more often called 'superquick fuze' or 'intantaneous fuze' can be seen on the very simple French mine-thrower fuze on the left, and schematized on the right. In this example, the only safety mechanism is a safety pin that was sheared by the rod when hiiting the target. It is intersting to notice on the left tha a variant existed for this superquick fuze with an additional delay !!! One must remember that in the case of trench artillery the use of sensitive superquick fuzes was dictated by the nature of the grounds and low projectile speeds and not by the need to maximize surface effects. In the other example top left (French I.A. fuze), the long rod has been replaced by a short one, the whole percussion mechanism and pyrotechnics being located on the top of the long fuze, and linked to the shell body via an explosive wire. |
Varitaions of the French superquick fuzes | Theoretical scheme of a typical German superquick fuze, that usually kept an ogival shape, sometimes elongated. | 1917 version of the German Fieldgun superquick fuze 'EKZ17' |
Shrapnel shells were in 1914 the main ammunition in use by the fieldguns of all the fighting nations. Just as with the older fragmentation shells, the efficacity of their anti-personnal effects was dependant of the position they bursted just in front of their target, in order to sprinkle steel fragments and lead balls on it. Since there is no impact of the shell with the target to give the signal for the burst, the fuze had to be a precise mechanism integrating a count down.
The role of the 'time fuzes' devices was to trigger the explosion at the end of a given lapse of projectile flight time (generally from some seconds to almost a minute), corresponding to the distance needed, given the knowledge of the projectile speed.
Pure time fuzes were generally limited to the use of Anti-Aircraft artillery, where one wants the shell to burst around the flying target but where it is important that an unexploded shell does not explode when landing back on friendly land. Most of the time, these systems were associated with a percussion mechanism, making these fuzes 'Time an Percussion' fuzes.
Three main types of time fuzes, were in use during WW1. Two of them were based on the slow and regular combustion of 'pulverine' (compressed gunpowder) track with an approximate speed of 1 cm a second, and the third one appeare lately and was based on clockwork mechanics :
Tubular time fuzes
This kind of time fuze was exclusively used by the French artillery, for instance with their famous fuzes '22/31 mod. 1897' (whose wartime scheme is shown at left, and a surviving example at right), or the '30/55 mod.1889'. The following explanation is made for the first model, that was equiped of an additional classic percussion fuze device in its tail. This particular fuze thus was a 'double-effect' (or 'time and percussion') one. |
Operation of the tubular time fuzes :
This system, called 'French Time System', was derivated into several fuses models until WW2.
Fusing spiral groove of a French 25/38 Mle 1880. The lead inner barrel has been pierced at the place of a graduated cap hole | Family picture of several French fuzes derivated from the French Time System, including some pre-WW2 fuzes. | Fusing spiral groove of a 30/55 Mle 1884 French fuze |
Revolving discs time fuzes
Operation of the revolving discs time fuzes :
The setup of these fuzes operation was always made by a preliminary rotation of the graduated mobile disc, placing the wanted duration of flight (in seconds or in hectometers) in front of an index engraved on the fixed disc. Specific devices existed to fix the disc to the set rotation before shooting, so that it did not turn during flight under the effect of the shell spin.
The maximum set-up time could be increased for long range guns in specific fuzes by using a slower burning composition for the gunpowder track, or by increasing the number of discs.
The combustion of all these gunpowder tracks and elements generated fumes, so that multiple windows were machined in those fuzes in order to let the gasses escape.
Superb section made by Alain Dubois of a British n°80 time and percussion fuze. See the communicating channels between the discs | Revolving discs German HZ05 time and percussion fuze : the destroyed model shows the sliding grooves of the disappeared mobile disc | Opened British n°80 time and percussion fuze, nice view on the central housing where the time pellet was located. |
Clockwork time fuses