THE MAIN TYPES OF WW1 FUZES AND THEIR MECHANISM

Version francophone


German time fuse Dopp Z 92, scheme
Introduction

Main categories of WW1 fuses

The use of primers with modern HE shells

Inertia mechanisms and percussion pins

Safety and arming mechanisms
Springs and pins : basic arming systems
Stirrups and ramps : inertia arming system
Pyrotechnic arming systems
Centrifugal force arming systems

Percussion fuzes systems
Percussion fuzes systems without delay
Delayed percussion fuzes systems
Super-quick fuzes systems

Time fuze systems
Tubular time fuzes
Revolving discs time fuzes
Clockwork time fuzes systems


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Introduction : creativity at the service of horror...

N° 80 British fuse (1916), with time mechanism graduated from 0 to 22 seconds
An artillery fuse is a device intended to trigger the deflagration of the inner charge of the projectiles, at a specific moment during flight or at the impact.

This much important mission gave to this tiny part of the shell one of the most important roles for the good operation of all the giants, guns and projectiles, that are spoken about in y spoke about in the other pages of this website.

The fuzes that can still be found nowadays in the ploughings, embedded in the earth or chalk and half destroyed are therefore 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 familirize 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...


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Main categories of WW1 fuzes

Several kinds 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 :

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 shot (humidity, shocks, corrosion, ...) and during its use (huge accelerations and decelerations, hugh 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.


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The use of primers with High Explosive shells

Détonator (or 'relay charge') screwed onto the fuse tail and  introduced in the shell in order to help the detonation of the main chargeThe 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 charge 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 fuze pyrotechnic line : from the left to the right, the fuze itself, the adaptator screw ring, the small sarter usually screwed on the fuze tail, and the bigger intermediate primer 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

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Inertia mecanism principle

German destroyed discs time fuse, the percussion pin is easily seen in the center of the pieceThe 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 'detonator 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 :
  • a small free-sliding inertia block (or 'graze pellet'), maintained at rest pressed against its chamber rear wall by a 'safety spring' (or 'safety creep spring'), beared a 'detonator cap' (or 'starter') containing mercury fulminate.


  • At impact time against the target, the graze pellet was violently propelled forward by an inertia force sufficient to compress the safety spring, allowing the contact between the detonator and a fixed 'percussion pin' attached to the chamber front wall, igniting a flame.
Bacic principle of the fuzes inertia mecanisms
Igniting system of a 30/55 T&P French fuze This same principle was applied both for :
  • the percussion mechanisms (called 'percussion systems') that were supposed to be activated by the shock of the arrival of the shell on its target, triggering the shell explosion


  • the arming mecanisms of the fuzes safety systems, or the igniting systems of the time ring powder tracks of the pyrotechnic fuzes (then called 'time pellet'), that had to be activated at the shot departure inside the gun barrel under the action of the violent initial acceleration. These systems are sometimes called 'concutor'.

Time pellet system of a French 30/55 time and percussion fuze. On the picture, from the left to the right : the percussion pin, the safety spring, and the detonator cap.

In this last case, the apparatus was turned upside down so that the mobile graze pellet was moving backwards.



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Safety and Arming mechanisms

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.

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.

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Percussion fuzes systems

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.

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Time fuzes systems

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 :

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