Impact Fuses

[mhurst]

Watching a film recently showing the operation of the shrapnel shell fuse demonstrated how safe it was for the gunners, since it was basically clockwork operated. Provided that there wasn't an inordinate delay in getting it into the breech and firing it, all would have been well.

But what about the later impact fuses for high explosive shells? I'm not sure how these were armed, but it must have been done by hand and was therefore inherently a dangerous procedure. How sensitive were the fuses? If a gunner slipped in the mud after arming a fuse and the end of the shell hit the gun frame, was there a danger of it exploding, or would this only happen under the much greater pressure of the shell hitting the ground, even in the mud? In WW2 bombs were armed either in the bomb bay or while actually in flight, which made handling on the ground much safer, but are there any reports of tragic accidents happening with fused artillery shells?

[Terry_Reeves]

Melvin

They were armed in flight, and depending on the fuze, used the principles of "set back' or spin. In the former, the inertia associated with the accelerating projectile was (and is) used to unlock the safety features. Spin uses centrifugal force imparted by the spinning projectile to start the arming process. In both cases arming is completed outside the barrel.

TR

[TonyE]

There is a misconception here that shells were armed before they were fired. This was not the case.

British shrapnel shells were not fuzed with a clockwork mechanism but by a powder time fuze.

When a shell was fired, the impulse of the rapid acceleration of the shell "set back" a needle in the fuze which struck a percussion pellet and ignited the powder train. This burned and flashed through to the second powder ring (depending on the time set on the adjustable fuze ring) which in turn ignited the gaine and detonated the explosive content of the shell.

HE shells were fuzed "Time and Percussion" so could be set to burst either at a pre-set time (= range) or on striking the ground or other object. They were handling and bore safe until after they were fired. All fuzes have a safety mechanism to allow for handling, dropping or other accident up to hte point they are fired. This can be a shutter mechanism that covers the percussion pellet, a centifugal mechanism that keeps the firing pin and the pellet out of alignment or any number of other devices.

Regards

TonyE

oops, posts crossed!

[centurion]

Explosive shells have not been "pre armed" since sometime in the late 17th century. A major problem (and hence danger) was a misunderstanding as the optimum way to light the fuse on the shell. Originally one gunner would reach into the mouth of the mortar or howitzer with a lighted port fire and ignite the shell fuse. He would then step smartly back whilst his colleague fired the weapon. Of course if the weapon misfired (damp powder perhaps) the gun crew would be left with a large shell fizzing away on top of an unexploded charge and about to explode. This could be an embarrassment but probably not for long. It then became the practice to do away with the two stage ignition process. The shell would be loaded with the fuse facing the charge so that the flash from the charge would ignite the fuse as it sent it on its way. Unfortunately the force of the explosion could on occasion force the fuse deeper into the shell causing it to explode prematurely, sometimes just as it was leaving the muzzle. At this point it definitely became a weapon of self destruction. Around about 1700 it was discovered that none of this was necessary, the flash when the gun was fired sent a wash of flame right around the shell and would ignite the fuse even if loaded facing away from the charge. At the same time fuses were developed into box wood tubes (often tapered) containing slow burning powder. These were calibrated and marked with notches so that they could be cut to give the appropriate burning time before insertion into the shell. Fuse setting was born.

As artillery developed and reliable and relatively safe percussion components were introduced different mechanisms for igniting a fuse were introduced (in part of necessity with the introduction of breech loading and rifled guns which eliminated the windage and wash of flash that could ignite a fuse. The boxwood fuse evolved (initially often posthumously by pioneer French naval gunners) into the type of ring fuse that Tony has described (although like the BBC one has to say that other types of fuse were available). Fuse times usually had to be set before firing. this was in the main by turning a ring so that a particular hole in the fuse train faced an ignition hole. Mechanical fuse setters were devised to to do this just before the shell was loaded into the breech. However shells were never set in a way that they could explode until they had left the muzzle and were a long way away , gunners tended to be quite paranoid about that.

Clockwork was never used - it simply could not withstand the shock of firing. In the Far East ingenious clockwork fuses had been developed using as a basis clock mechanisms imported from the West. These have been claimed by China and Japan but probably were stolen from the Koreans (who seem to have been the major pioneers of military technology in the region) but these were only used in static devices such as land mines, petards and time bombs. It wasn't until late WW2 that shells were equipped with detonation devices that did not rely on either a chemical fuse or a percussive device (or both) when British scientists and technologists developed electronic systems that were small enough to fit in a shell and rugged enough to withstand firing and the Americans developed ways of mass producing them so that the radar proximity fuse came into being (and not just for AA use)

[mhurst]

My thanks to you all for your most informative replies. I stand well and truly corrected.

Melvin

[mhurst]

Clockwork was never used - it simply could not withstand the shock of firing. In the Far East ingenious clockwork fuses had been developed using as a basis clock mechanisms imported from the West. These have been claimed by China and Japan but probably were stolen from the Koreans (who seem to have been the major pioneers of military technology in the region) but these were only used in static devices such as land mines, petards and time bombs. It wasn't until late WW2 that shells were equipped with detonation devices that did not rely on either a chemical fuse or a percussive device (or both) when British scientists and technologists developed electronic systems that were small enough to fit in a shell and rugged enough to withstand firing and the Americans developed ways of mass producing them so that the radar proximity fuse came into being (and not just for AA use)

A search of Wikipedia for artillery fuses has thrown up the British Thiel pattern clockwork fuse, produced between the wars, but based on a pre-1914 Krupp design (there were Swiss and American designs as well). It was extremely complicated, and must have been costly to produce but, presumably, must have been able to withstand the shock of firing.

Melvin

[Ogilwy]

Time mechanical fuzes are both hard to manufacture and have a much greater failure rate than either Time Combustion or more modern Electronic Time Fuzes (ETF). They also have the added problem for us of being the single most dangerous type of blind you can get. A single piece of grit can stop the mechanism and movement of any type can restart it (which is a bad thing)!! Another reason why the disturbing of shell whilst on the battlefields is not advised.

Fortunately the manufacture of them especially during the wartime conditions was so difficult that they were not in great use but enough still exist that they do crop up occasionally. Talking to the de-mineur these are one of the only items that they 'Blow in Situ' without exception.

As centurion says the AA use of ETF or Proximity fuzes came about at the end of WW2. The British had a Top Secret project at the time called Green Archer which was the protection of London using radar controlled guns and Prox Fuzes.

The modern criteria is that at least three separate safety arrangements are in place in the fuze up to the point of firing. During WW1 at least two were in place even for such dangerous fuzes as the Hotchkiss base fuze (6 Pdr tank gun) (a lead shear strip and a creep spring). The usual set back, centrafugal force, set forwards and mechanical safety (such as clockwork) were all used and actually the fuzes were very safe, (for the period), with any mk's or Models that proved problematic being withdrawn and replaced in short order.

Regards,

Rod

P.S. Time mechanical scares the Cr*p out of me, I hate dealing with them !! Oh and Hotchkiss have the same effect !!!!!

[nigelfe]

Correct, Germany had developed a mechanical time fuze pre-WW1. UK basically adopted this, first used in the No 208 that entered service about 1939 for the 3.7 AA gun. One of the problems in the Battle of Britain was that there were still lots of igniferious fuzes and with the high (relativey speaking) target height and range the error in the fuze burning time made Height of Burst accuracy somewhat less than needed.

Safe Arm mechanisms for fuzes use various mechanisms that exploit inertial and centripetal forces to unlock as the shell accelerates and starts spinning. In WW1 safety pins in the fuze nose that were removed just before loading were also used.

Shrapnel used T&P fuses, HE did not.

[nigelfe]

As centurion says the AA use of ETF or Proximity fuzes came about at the end of WW2. The British had a Top Secret project at the time called Green Archer which was the protection of London using radar controlled guns and Prox Fuzes.

Not entirely correct (today's understatement). ETFs weren't invented untill the 1970s, the first UK one was the L132 that is still in use (until all the Electronic Fuze Setters finally die). Proximity (AKA 'VT') fuzes are a totally different technology. For starters ETF are passive (like time fuzes), Prox is active (it has a little TX/RX).

Green Archer? Double used of a colour codeword doesn't seem likely, colours weren't used for operational nicknames (which were single word anyway. Green Archer was 'Radar, Field Artillery No 8' that entered service c. 1959 for mortar locating. Radar controlled guns were used from 1939 onwards by RA regiments with continuous improvements. The V1 defence operation (which was in SE England not around London) and relied on radar FC and VT fuzes was called DIVER.

[Ogilwy]

Just spent the last 30 minutes discussing L132's and arrive back to more ! Remember that modern Prox has a time element to turn it on at the correct time. A highly reliable source gave me the Green archer for the post war Prox / VT used in conjunction with a Radar Net for SE England so I'll email him later and ask for verification. It was during a discussion on the use of 6" Naval barrals and ammunition for HAA around London.

We also found a 3" Gun site on Shooters Hill with the holdfast still in place. Unfortunately no ammunition except some .303 Mk VI SAA but that was interesting and a whole different story.

i have PM'd you separately.

Rod

[centurion]

Correct, Germany had developed a mechanical time fuze pre-WW1. UK basically adopted this, first used in the No 208 that entered service about 1939 for the 3.7 AA gun. One of the problems in the Battle of Britain was that there were still lots of igniferious fuzes and with the high (relativey speaking) target height and range the error in the fuze burning time made Height of Burst accuracy somewhat less than needed.

Safe Arm mechanisms for fuzes use various mechanisms that exploit inertial and centripetal forces to unlock as the shell accelerates and starts spinning. In WW1 safety pins in the fuze nose that were removed just before loading were also used.

Shrapnel used T&P fuses, HE did not.

I assume you are referring to the Thiel mechanical fuse, used by Germany in WW2 although essentially a pre WW1 design. I've never really considered this clockwork (although it could certainly be classed as such) as it's much more akin to the basic kitchen timer (or a self timer on an old camera). These had a maximum setting of 30 seconds but even with their basic simplicity the shock of firing could cause jamming. They didn't start ticking until after firing. Setting was by turning a ring much as on the chemical fuses. I believe that the 208 fuse was not used operationally until quite late in the WW2 when it replaced the 199 Fuse.

I've always believed that Green Archer was a Radar guided Automatic AA gun of which development was abandoned post WW2. Hogg has a write up (and photo) in one of his books. It was intended to be part of a secret project intended to protect London against V2 ballistic missiles. The theory was that once its engine had ceased firing the trajectory of a V2 was entirely predictable so that provided that it could be detected and the calculations done quickly enough AA guns could be selected and directed to fire on an intercepting vector. Initial calculations suggested a hit rate of between 30 to 50 % which was deemed good enough to make the thing worthwhile. An early electronic computer (Turing wasn't the only pioneer in this field) was developed to do the calculating. However the scheme was abandoned when someone pointed out that a V2 on its downward trajectory consisted very largely of empty fuel tanks and whilst hitting these might deflect the missile it wouldn't stop the warhead hitting London somewhere. Hitting the warhead was much more problematic and success rate in single figure percentages was the best that could be predicted. The scheme was put on the back burner and although development of the gun system continued as a defence against jet bombers it was abandoned post war in favour of missile systems. I learned about this when a graduate apprentice at Rolls Royce which at that time had the largest computer set up in Europe and agreed, with government backing, to make a short film on the history of computers in Britain - I landed (got lumbered with) the job and unearthed the details of the computer developed for the project. At this point a voice of authority said stop as parts of the project were still regarded as secret even in the late 1960s

[mhurst]

I learned about this when a graduate apprentice at Rolls Royce which at that time had the largest computer set up in Europe and agreed, with government backing, to make a short film on the history of computers in Britain - I landed (got lumbered with) the job and unearthed the details of the computer developed for the project. At this point a voice of authority said stop as parts of the project were still regarded as secret even in the late 1960s

That's another story, but it sounds fascinating. Were details of the early computer ever published?

[Ogilwy]

Centurion,

My information is the same - Green Archer was the whole system and incorporated the newly developed Prox fuzes and I believe Time fuzes as well. I wonder if it had an automatic setter?

The Thiel Time Mechanical Fuse is one of those that really scares people in my line of work. They were very well made but still suffered from quite a failure rate. There's not much that I'd rather deal with less than a Time Mech fuzed shell!

Regards,

Rod

[centurion]

I learned about this when a graduate apprentice at Rolls Royce which at that time had the largest computer set up in Europe and agreed, with government backing, to make a short film on the history of computers in Britain - I landed (got lumbered with) the job and unearthed the details of the computer developed for the project. At this point a voice of authority said stop as parts of the project were still regarded as secret even in the late 1960s

That's another story, but it sounds fascinating. Were details of the early computer ever published?

No I could only pick up odd references. At the same time in Germany Telefunken developed a computer as part of the Wasserfal ground to air missile system to allow continuous course adjustments to be made to the missile's flight as the target moved, changed speed, altitude etc etc. This was the first computer to use a CRT screen to display its results. The last record of this machine was it being packed into a Soviet Lorry and shipped East along with the German technicians involved. All was silence after that - Stalin didn't believe in computers.

[nigelfe]

Seems extremely unlikely that the same colour nickname would be used for two different things within 15 years, having used them I can say confidence that Green Archer was Rdr FA No 8 used for mortar locating, Wikipedia has a good entry (I would say that because I wrote most of it). The only Green AA system that leaps to mind is Green Mace, a highly automated HAA gun developed in the 1950s.

The authoritative source on UK AA history is Brig NW Routledge 'Anti-Aircraft Artillery 1914-55'. He doesn't miss anything major and makes no mention of 'Green Archer'.

Both Fze 209 (used with 4.5) and 207 (with 3.7) were mechanical time. MT fzes were developed by the outbreak of war, mass production was an issue, then in late 1940 No 207 had to be withdrawn for modification because worn barrels (and lack of spare barrels) resulted in fze malfunctions and muzzle prematures (similar thing happened in 1916).

Machine Fze Setter No 11 entered service in 1943 as part of the fully automated 3.7 Mk IIC.

Technically speaking VT with a mechanical timer was called Controlled VT (CVT) and appeared in the 1950s. The timer was a safety device to prevent early bursts and later a bit of simple ECCM, not a backup airburst function. The fze length was designed to switch-on the radar TX/RX 5 secs before the predicted Time of Flight end, it wasn't a precision timer.

[Ogilwy]

We are however straying well off target in date. So back to the 101 and 106 not forgetting the lovely GR Z 92!!