Artillery Question

[Robohn]

What is the difference between 105mm and 105mm VT? I see that VT costs more, but what is it? Why is it better? Thanks for any info.

Robohn :confused:

[Moriarty]

Originally posted by Robohn:

What is the difference between 105mm and 105mm VT? I see that VT costs more, but what is it? Why is it better? Thanks for any info.

Robohn :confused:

The variable-time fuse allows the shell to go off above the ground. It annoys the German infantry to death.

The arty grogs can fill you in on the details, if you're interested, but that's the Reader's Digest version.

[ June 17, 2002, 06:46 PM: Message edited by: Moriarty ]

[Redwolf]

It is not variable-time, VT is the stuff with a real radar device in it. Basically you get airbursts like in treebursts but without trees.

Extremly effective in CMBO, against infantry, but also open-top vehicles and apparently buildings, too.

[JonS]

Originally posted by redwolf:

It is not variable-time, VT is the stuff with a real radar device in it. Basically you get airbursts like in treebursts but without trees.

Actually, it is "variable time." Allow me to digress, then I'll come back to the point.

In the late 1800's a type of shell was developed to be very effective against troops in the open. This type of shell had numerous ball-bearings (or similar) in it, and a fuze that had a user settable timing element in it. The idea was to get the shell to explode in the air in front of the troops in the open, showering them with the ball-bearings, and decimating their ranks. These shells were called 'shrapnel' (and incidentally, this is the only strictly technically correct use of the word shrapnel - the bits that come off HE shells are 'fragments'). Manufacturing shrapnel was an expensive and fairly slow process, and making the fuzes even more so. On top of that, training the gunners to be able to properly use them was tricky and expensive in terms of $$$ and time. However, for the little wars of the late 19thC and early 20thC this was fine, and the effect against the fuzzy-wuzzies was always gratifying.

Then came WWI. Men went under ground, making shrapnel shells less effective. Even worse, armies expanded rapidly to huge proportions, and it was felt that these citizen armies were too thick to be able to comprehend the complexities of getting a round to explode in the air at the right distance from the enemy. Also, shell consumption went through the roof, and it was easier and quicker to make the quantities required if they were just HE with a point-detonating fuze. And thus it came to pass that the shrapnel shell passed into history.

But. Late in WWI, and during the 1930's, it was found that getting shells to explode in the air was a good thing after all, and actually, all these guys who had been clerks and bankers and run their own businesses and farms weren't that thick after all. So, a time fuze was developed (or re-developed if you like). This allowed such nifty things as getting AA rounds to go off at a set height increasing the chances of bringing down enemy aircraft, and popping smoke rounds in the air to get better spread of the canisters, and best of all they could be screwed into the front of an HE shell to make it explode in the air and function nearly as good as the old shrapnel shells.

The new time fuze (technically called Mechanical Time) had a screw on the side, and after the adjustment of the fire mission had been completed, all the guns in the battery set their time fuzes to the same time (via the screw) and proceeded to fire their rounds. And, exactly at the time that the fuze was set to, the round would go off. Now since the guns all have slightly different characteristics, as do the fuzes and the shells, some fired further and faster, others fired shorter and slower, but since they all had the same fixed time interval on their fuzes, the rounds all exploded at the same time. For some rounds this meant the fuze went off too early, causing the round to go off too high, and dissipating its effect. Others went off to late, and just exploded when they hit the ground - like a regular HE shell. But, in general, they went off at the right height and so were deemed worthwhile. Also, they could be used with regular HE shells thus simplifying ammo production and supply.

Then along came WWII, in which those nasty Germans tried to make us eat sauerkraut. Again. But this time the sneaky little monkeys got the Japanese to help them, and they both had the temerity to develop faster planes. The Blighters!

Anyway, this meant that the old method - shooting a metric buttload of HE with the mechanical time fuze at passing aircraft - wasn't as successful as the salesman had said it would be. But since he'd nipped off to retire in Bermuda, there was no-one to whine to. So, choosing Plan B, the Western Allies (and it really was an inter-Allied development involving the UK, Canada, and America each making important contributions. But even so, they weren't prepared to share with those uncultured Soviets) produced an new type of fuze, and had it ready in 1943 or 1944 (I forget which). This one had a radar thingamy in the nose, which sent out regular pulses, and when it detected that it was within a preset distance of something solid it detonated. This "pre-set distance" was that calculated to be within the lethal envelope of the expanding cloud of fragments from the HE shell to which the fuze had been attached, thus greatly increasing the chances of damaging or destroying the aircraft it was aimed at. Since the gunners didn't have to calculate how long the round was going to be in the air before it came close enough to damage an aircraft, because each fuze went of when it felt like going off, the fuzes each ran for a different - or variable - length of time. Which was quickly reduced to "Variable Time", or the even more user friendly "VT". {Edit to add: just in case you miss it, this was the bit where I got back to the point.}

This came as a bit of a shock to the Japanese in the Pacific who were hell bent on bringing America to her knees by forcing her to shoot metric buttload after metric buttload of HE shells with the regular-old, fixed time, Mechanical Time fuzes. This was working just dandy until those uncouth, under handed 'Mericuns started using VT fuzes. Then, instead of metric buttloads of shells being used, it was metric buttloads of Japanese pilots who were being shot down.

Then, some bright spark had a bit of an insight and noticed that the ground was just as hard as an aircraft. Or perhaps even harder - ever seen a plane hit the ground? Which came off worse? Using this blinding insight into the physical world he reasoned that a VT fuze, attached to the front of an HE shell, 'should' go off at the optimum height of exactly 40m above the ground. Every time, every round.

So he tried it. And it didn't work . Bah! just kidding. It worked great . So, fuzes were developed to fit all the common rounds used by the Allies - 105mm, 155mm, and 25-pr. But then someone else had a thought: what if we use these, and one doesn't work? And, what if those sneaky Germans find the one that didn't go off? And what if, with their well know disregard for copyright laws (you thought the Chinese were bad? You should have seen these guys in action!), they copied it! Without paying royalties!

So, with the fear of lost royalties before them, the Allied Combined Chiefs of Staff wouldn't allow the VT fuzes to be used except in cases where it could be guaranteed that the sneaky Germans couldn't get their copyright-infringing mitts on one. This pretty much restricted use of the VT to behind friendly lines, or over the open sea. The former was tried a few times, but each time it caused a high level of user complaints, and the effects on the enemy were negligible. Since Operation Sealion had been called off in 1940 there wasn't much call for the latter.

Then late in 1944, the Germans - warm hearted guys that they are - gave the Western Allies a Christmas present. This involved relieving them of responsibility of looking after those weird mountain people from the Ardennes. But, since it was a bunch of Hillbilly 'Okies from the US looking after that bit of Europe they felt quite at home among all the six-fingered folk, and really didn't want to go back and hang out with all those fancy city-folk in Brussels and Amsterdam. So, they decided to stay. But it was touch and go for a bit, until Eisenhower (or someone) said

Oh, to hell with the royalties - let's see how good these things are!

As an aside, its a shame that this quote has largely slipped out of memory as it is, in my opinion, easily as rousing and inspiring as other more famous quotes like "We shall fight them on the beaches!", or "This was their finest hour", or "I shall return". Certainly it was more literate than "Nuts!"

Anyway, that about wrapped things up - so to speak - for the Germans' Christmas party. After the Western Allies started using VT they sulked, taking their toys over to Hungary to play with the Soviets who, as we already know, were too uncultured to have VT.

There you have it. A brief history of VT.

Any questions?

Regards

JonS

Edit: Ok, ok, there were a few spelling mistakes too ...

[ June 17, 2002, 09:57 PM: Message edited by: JonS ]

[Pak40]

what Jons said

[PiggDogg]

Jon,

Thanks for the informative and entertaining history lesson on VT.

Cheers, Richard

[Moriarty]

don't say I didn't warn ya.

Seriously, though, thanks for the info Jon.

[ June 18, 2002, 12:25 AM: Message edited by: Moriarty ]

[JonS]

Glad you liked it.

Links to current US fuzes:

Click Here (search page for "Variable" or "Proximity") The relevant bit is from Slide 77 onwards.

Or Here Pretty pics of fuzes. M728 is the VT fuze. M563, M564, and M565 are the Mechanical Time fuzes - if you look closely you can see the time divisions around the nose of the fuze. You set it much like setting an egg timer.

Regards

JonS

[ June 17, 2002, 10:23 PM: Message edited by: JonS ]

[JasonC]

I have only two quibbles to Jons excellent and entertaining history of the subject. One, shrapnel is rather older than the late 1800s. 100 years older. The term comes from the name of a colonel in the royal artillery, colonel Shrapnel, who came up with the balls inside the shell idea.

But that isn't quite right either, because they already had balls inside cannons, they just used them as canister fired level, like a shotgun. Howitzers fired exploding shells (the term "shell" stems from it being hollow to contain explosive, instead of solid roundshot) at long range instead.

These had fuses hanging out of them like Yosemite Sam uses on the crazy rabbit. The fuse was cut to the right length to burn for the right length of time, for the howitzer shell to explode in the air over the troops it was aimed at. Above all, you didn't want the shell to hit the ground and bounce or have the fuse go out or fall out etc - before it exploded. It was keystone cops stuff, and not very effective.

What Shrapnel did was combine the idea of canister with the idea of howitzers, producing a hollow shell containing the same sort of assorted musket-ball sized projectiles as in caseshot. He actually called the thing "spherical case". But everybody else just called it Shrapnel after the guy who came up with it. Eventually the capitalization of the "S" disappeared. All of that is quibble one.

Quibble two is the idea that shrapnel went out of fashion in WW I because it was harder to make and use. Jons mentioned the real main reason - because it simply was not effective against dug in troops. Shrapnel was used extensively in WW I, especially by lighter guns, and it had dismal results.

It was much more effective to put a heavy HE shell well into the ground with a delay fuse. That sent out a powerful horizontal shock wave, which could cave in the side of trenches without direct hits. It also cut wire much better, blowing up the stakes holding it in. HE was not preferred for simplicity, and by the end of WW I the gunners of all the major powers used far more sophisticated methods, more effectively, than colonial era armies had.

The rule still today is that delayed fusing is preferred whenever the target is dug in. Air bursts or ICM bomblets are preferred for targets in the open, above ground. The real thing that led to a comeback for airbursts was simple the more mobile nature of WW II, which meant there were more occasions for catching the enemy out of any sort of hole.

For what it is worth.

[ June 18, 2002, 05:20 AM: Message edited by: JasonC ]

[John D Salt]

Originally posted by JasonC:

I have only two quibbles to Jons excellent and entertaining history of the subject. One, shrapnel is rather older than the late 1800s. 100 years older. The term comes from the name of a colonel in the royal artillery, colonel Shrapnel, who came up with the balls inside the shell idea.

[snips]

Indeed he was a Major when he first thought of the idea -- when in Napoleonic mood, some of my wargaming circle can still be heard mumbling about "Major Shrapnel's spherical case".

If I may raise a quibble of my own -- although the tradition that "VT" stands for "Variable Time" is now so soundly entrenched that there is no hope of moving it, it is not the origin of the designation; "VT" was merely the arbitrary (US Navy, I believe) identifier assigned as a project code.

I can't at the moment put my hand on a source for this, so disbelieve me if you like, but common sense should tell you that a proximity fuze does not measure time in any way, so calling it a time fuze is a bit daft (does anyone call mechanical time fuzes "variable proximity"?)

The "VT = Variable Time" convention was first told to me by no less an authority than a Petty Officer Gunnery Instructor at HMS Excellent, Whale Island, when it was still the RN's school of gunnery. Mind you, he also told me that "HE" stood for "High Effect", which it may well have done for the 4.5" Mk 6, but doesn't usually.

Other famous "entrenched" back-formations that seem to have gained official sanction are the idea that "CS" (as in CS gas) stands for "Composition, Smoke" (which I've heard from a battalion NBC officer), and that "Jeep" is derived from the letters "GP", signifying "General Purpose" (a story that gets the approval of so august an authority as the Oxford English Dictionary). There are probably lots of others.

All the best,

John.

[edward_n_kelly]

Originally posted by JasonC:

(Edited for brevity)

Quibble two is the idea that shrapnel went out of fashion in WW I because it was harder to make and use. Jons mentioned the real main reason - because it simply was not effective against dug in troops. Shrapnel was used extensively in WW I, especially by lighter guns, and it had dismal results.

It was much more effective to put a heavy HE shell well into the ground with a delay fuse. That sent out a powerful horizontal shock wave, which could cave in the side of trenches without direct hits. It also cut wire much better, blowing up the stakes holding it in. HE was not preferred for simplicity, and by the end of WW I the gunners of all the major powers used far more sophisticated methods, more effectively, than colonial era armies had.

Actually one of the biggest problems for any of the protagonists in World War One was the cutting of wire.....

Shrapnel shell was tried first but without much success, while initial fusing of HE was too unreliable. While it could be set for instantaneous effect in reality it was not - burying itself for a few feet before it exploded and lessening its effect by many orders of magnitude.

Until sufficient shells with reliable fuses (of the SQ or Super Quick) variety were available (in about 1917) results were extremely variable.

The Germans did not really have this problem - the West Front they were on the defensive in the main (or attacked in lightly defended areas like 5th Army in 1918) while on the Eastern Fronts the density of wire was just not there (and similarly the Turks and Austro-Hungarians)...

As to the use of Heavy HE shell - again the guns, ammunition and relaible fuses were in short supply until 1917.

Else why would there be so many dangerous objects unearthed each year in France.

[Redwolf]

Originally posted by redwolf:

It is not variable-time, VT is the stuff ...

I was posting with my brain switched off. What I meant to point out is that VT was not the only technology that achived airbursts in WW2, as pure timing, either triggered by shot or ground contact was common as well, although the VT as in CMBO was much fancier.

[Agua Perdido]

Originally posted by JasonC:

...Shrapnel was used extensively in WW I, especially by lighter guns, and it had dismal results...

I recall reading about the pre-war testing of shrapnel shells, I believe in Germany (no, I don't recall the source and for all I know this is a grog urban legend). The measure of effectiveness for the shells was the ability of the fragments to penetrate 1/2" pine boards during tests, which was assumed to be sufficient to kill or incapacitate a person. A post-war accidental detonation had fewer that the expected casualties, and further study demonstrated that humans were evidently tougher than 1/2" pine boards. Operational test and evaluation is tough.

(Especially if you're one of the "pine board proxies".)

Originally posted by John D Salt:

...I can't at the moment put my hand on a source for this, so disbelieve me if you like, but common sense should tell you that a proximity fuze does not measure time in any way, so calling it a time fuze is a bit daft...

A prox fuse does measure time, albeit indirectly. If you set the fuze to go off 40m above the ground, it effectively measures the time from when it is fired until it gets to 40m above the ground on the way down, at which time it goes bang. Since this time varies, based on the dispersion of the gun or variations between powder charges, the fuze is effectively "variable time."

(does anyone call mechanical time fuzes "variable proximity"?)

No one calls them that, but it's effectively what they are. They go off at a fixed time from leaving the muzzle, but variations in muzzle velocity/wind/whatever cause that detonation to happen at variable proximities to the ground.

That said, I'm willing to believe that "VT" began life as an arbitrary designator, especially given its US Navy origin.

Anchors aweigh,

Agua Perdido

[tar]

Re: Pine board story.

IIRC, I read about this in one of the information briefings in S&T Magazine back in the 1970s when SPI published it.

Re: VT = Variable Time

I also recall hearing that the use of the term variable time was chosen so that they wouldn't have the word "radar" in the description. Since radar technology was closely guarded, the powers that were didn't want any information about its use disseminated.

Digression: During WWII, MIT had a "radiation lab" set up in the physics department. The lab did research on radar, but the name chosen for the lab was designed to mislead casual spies into thinking the physicists were working on something impractical (like atomic weapons) instead of really useful (like radar).

[Michael Emrys]

Double post. [sigh]

Michael

[ June 19, 2002, 01:13 AM: Message edited by: Michael emrys ]

[Michael Emrys]

Originally posted by JonS:

...an new type of fuze, and had it ready in 1943 or 1944 (I forget which). This one had a radar thingamy in the nose, which sent out regular pulses

There was a long discussion of this in one of the military newsgoups last year, the upshot of which was that it was not actually a radar at all. But the discussion was sufficiently esoteric that I can't recall with precision what the exact principle is that it did operate on.

However, with a little digging I did come up with this:

Another method that was more logical and became the accepted means, was to develop a fuze which was capable of obtaining its own intelligence and of using it to ignite the shell. When assembled this fuze consisted of four major parts: A miniature radio transceiver, complete with amplifier and capacitor; a battery; an explosive train; and the necessary safety devices. The theory was that the fuze transmitter, alone, would not produce sufficient signal intensity, to trigger a thyratron tube switch. However, as the projectile approached a target the radio waves reflected by the target would gradually increase and come more and more into phase with the fuze-generated signal. Once the signal level was high enough, the fuze would know that the shell could do a maximum amount of damage, and the thyratron tube switch would be triggered releasing the energy in a charged capacitor and thus igniting the shell.

This was found here.

The difference being as I understand it (and I may not; as far as I'm concerned we are verturing deep into boffinland here) is that radar sends out a pulsed signal and the VT uses a simple unpulsed radio signal.

HTH

Michael

[ June 19, 2002, 01:17 AM: Message edited by: Michael emrys ]

[Ozzy]

hmm.... IMO would not work with pulses, as you must bring together two different signals (impulse and echo) with correct phase and amplitude to release the trigger. This could make the shell burst earlier, later, or never. So I assume you are right.

The other huge difference is that radar transceivers use pulses to detect direction and range from object by measuring wave travel time (distance) and electromagnetial field (vector), which is a completely different principle

[John D Salt]

Originally posted by Michael emrys:

[big snips]

The difference being as I understand it (and I may not; as far as I'm concerned we are verturing deep into boffinland here) is that radar sends out a pulsed signal and the VT uses a simple unpulsed radio signal.

Pulse radars use a pulsed signal. Continuous-wave radars, however, do not.

I wonder if anyone would object to calling the boffinish gubbins in the head of a VT shell a "CW range-only radar"? Or will they insist on giving full value to the logical conjunction in Radio Detection And Ranging?

All the best,

John.

[Agua Perdido]

Originally posted by Michael emrys:

There was a long discussion of this in one of the military newsgoups last year, the upshot of which was that it was not actually a radar at all...

It was not a "radar" in the sense that it didn't have the round screen with the lighted sweep going 'round and little "blips" lighting up that we've all come to know from TV and movies. Of course, neither did many early radars, which had all sorts of user-hostile display schemes before some bright bulb came up with the "Plan-Position Indicator" (PPI) display.

Note, the method you describe in your quote is quite legitimately a CW ranging radar. It sends out a continuous beam of RAdio waves, achieves a Detection when it receives a signal bouncing off something reflective, And Ranges it by going "pop" when the signal achieves a certain strength (via the assumption of the target's reflectivity to radio waves producing a return of a certain strength at a certain distance). Now, I'll grant that the VT fuze isn't as clever as to say, "there's a bogey bearing 260 true at 10 kiloyards," it only says "hey, there's something 10 yards away! bang!" But that still qualifies.

Originally posted by John D Salt:

...boffinish gubbins...

Save that kind of talk for the Peng Thread!

Agua Perdido

[JonS]

LOL - well, I was trying to keep it simple and easy to read. If you go through you will find any number of minor falsehoods and gross simplifications

Thanks anyway to all for the clarifications and corrections

I'm reluctant to bring the following up, as it might seem churlish, but Jason's comment:

Quibble two is the idea that shrapnel went out of fashion in WW I because it was harder to make and use.

got me wondering. I know shrapnel wasn't much chop against dug in troops, just as MTSQ or VT isn't recommended against troops with OHP now, but what I wondered was why I put in the comment about difficult to manufacture and train. So, I did some digging, and came up with the following:

Bidwell, S. (1970), Gunners at war, Arms and Armour Press, London. p.21

...[shrapnel] [a]s an artillery weapon for killing men it has never been surpassed. (It was only eventually abandoned in favour of the noisier but far less effective high explosive shell because it was difficult to manufacture and difficult to use, and becauseas a bullet-producer the machine-gun was proving more cost-effective)...

and on p.35

... Moreover, the larger part of the artillery consisted of shrapnel-firing 18-pounders, which were effective for killing men in the open at short range or in shallow trenches, but as siege weapons were poor and too difficult for the mass-produuced officers of the new armies to use. (A report of 1918 recommended a total conversion to H.E. as fifty per cent. of the shrapnel were bursting uselessly on the ground.)...

In addition, there was Jasons' (IIRC) contention, in a thread on WWI, that the new armies used at the Somme weren't given in depth training because it was felt that they wouldn't be able to comprehend it (again, IIRC).

So, that's part of the reason I put what I put, FWIW But, note that it doesn't contradict what Jason said either about being ineffective

Regards

JonS

P.S. regarding the 'never been surpassed' bit in the first quote from Bidwell ... remember the book is 30+ years old

Edited to add a link: Development of shrapnel

[ June 20, 2002, 08:49 PM: Message edited by: JonS ]