What does "VT" mean

[chiavarm]

In the artillery section some of the unit have "vt" after the description. What does it mean and what impact does it play in the game?

[Kingfish]

Variable timed. Basically, it is an artillery shell with a special fuze which causes the shell to explode at a preset height above the ground. This is highly effective against troops caught in the open or in fortifications without any overhead cover.

[YankeeDog]

Well. . . wrong forum (AFAIK, no VT in CMBB, since it's an American/Brit only weapon), but:

VT stands for "Variable Time", which is actually a bit of a misnomer.

It's actually artillery that has a small radar trasnciever set in the nose fuse. This transceiver sends out a regular signal, and when it detects that it is a certain distance from a large object (say, the ground, or an airplane), it detonates.

It was originally developed as an anti-aircraft fuse, but they discovered is also worked very well against ground targets, since you could set the fuse to, say, 10m, and get a perfect airburst every time.

This is absolutely DEADLY to troops without overhead cover, both in-game and IRL.

So most of the time, VT is dramatically superior to conventional-fused artillery. There are at least two places where VT isn't as effective, though. It doesn't work so well against troops in buildings (the buldings provide overhead cover, and it's also less effective against troops in trees -- the tops of the trees create a radar return that detonates the VT shells at too high an altitude, while regular HE quick fuse will often detonate in the tree branches, creating large numbers of secondary projectiles.

Cheers,

YD

[chiavarm]

Thank You!

[Other Means]

Originally posted by YankeeDog:

{snip}

it's also less effective against troops in trees -- the tops of the trees create a radar return that detonates the VT shells at too high an altitude, while regular HE quick fuse will often detonate in the tree branches, creating large numbers of secondary projectiles.

Cheers,

YD

Are you sure? I've used it with *great* success against troops in trees. I assumed the wavelength would be too long to get a consistent return off the foliage and with the shell guaranteed to blow at altitude it's assured a treeburst.

Willing to be proved wrong but that's the way it seemed to me.

[YankeeDog]

Come to think of it, I've never actually tested the tree thing CM.

However, I have it on good authority (Viet Nam Vet who was an FO for a 105mm howitzer battery) that this is true IRL.

It may be partially dependent on the density of the foliage -- IOW, a dense jungle canopy might be more likely to set off VT fuses than the more dispersed canopy of a temperate climate deciduous forest. I don't know.

Cheers,

YD

[flamingknives]

Actually, AIUI, VT doesn't actually mean anything. It's the code letters for the project, and someone called it Variable Timed and that stuck.

Calling it that is useful because is misleads the enemy into thinking that it is some form of improved timed shell, which it isn't

[Guest Mike]

Yep - I read that somewhere too - VT was nothing to do with "variable time" originally, but it fitted well & was good camouflage.

Damned if I can find the reference now!

Edit - here's a good description of hte development: http://www.history.navy.mil/faqs/faq96-1.htm

Note that US development was undertaken by Section T, NDRC, at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington - I think that's where the "T" comes from.

Edited again:

"The USN was interested in the idea and took over the responsibility for development. Section "V" of the Bureau of Ordnance was in charge of the programme and they allocated it the code-letter "T", which led to it being called the VT fuze. "

- from http://www.j-aircraft.com/faq/navy_misc_info_pt2.htm#VT%20Fuses%20etc

and attributed to Hogg's "British and American Artillery of WW2" - which I have and which may be where I remember seeing it originally.

[ February 15, 2005, 04:33 PM: Message edited by: Mike ]

[flamingknives]

Yes, I'm pretty sure that Hogg's book was where I read that tidbit.

[JonS]

Heh. Waddya know. That's my new thing for the day.

As it happens, 'Variable Time' does make sense in terms of the fuze. Normal timed fuzes are set to a specific length, and will go off that many seconds after the shock of firing, regarless of the height they are at that point in time. So the gunners need to figure the trajectory, then back track along it to get the desired HOB (Height of Burst), then convert that distance to a time, then apply that as a fuze setting. And every shell fired on that mission will use the same setting 'fixed time' setting. With VT, the fuze itself works out how long to run for to get the exactly desired HOB, thus each shell will run for a slightly different, or vairable, amount of time.

Here's something I wrote on VT back in CMBO daze

[flamingknives]

Except the fuse isn't running - it's not timing anything so the length of time is irrelevant. The time of detonation may vary, but the fuse does not 'work out' how long to run for. It just goes off when it receives the correct signal.

You could call it a remote impact fuse and be just as accurate

[JonS]

Originally posted by flamingknives:

Except the fuse isn't running - it's not timing anything so the length of time is irrelevant. The time of detonation may vary, but the fuse does not 'work out' how long to run for. It just goes off when it receives the correct signal.

Yes, I know that.

[flamingknives]

And I was just being picky. It's not like I'm not known for that.

[Guest Mike]

Actually the fuze is running - it's sending out its little radio signals and waiting for a strong enough return to tell it to go boom!

So in a very real sense "variable time" is quite accurate - the fuse has only 1 action setting - "on" - but the point at which that setting operates is at a variable time - the variable being how long until it gets an appropriate response.

One good picky deserves another I say!!

[chiavarm]

Originally posted by JonS:

Heh. Waddya know. That's my new thing for the day.

Here's something I wrote on VT back in CMBO daze

Do you kow if CM uses/simulates the timed fuse mentioned in your article for normal HE or would that still be condsidered VT?

[VTARNGPB]

and i thought this was just another joke to pick on us vermonters...

[Dandelion]

How did the running fuze make it superior to the fairly commonly used bouncing charges? I mean the various types that were set to go off after a violent collision, bouncing from the ground and creating a post-bounce airburst. Still in use, as they are.

Asking out of genuine curiosity.

Cheers

Dandelion

[flamingknives]

How exactly do you propose to make a 12kg shell falling at a fairly steep angle bounce?

Furthermore, the timing in such shells cannot be clockwork (and hence accurate) as the bounce would destroy the delicate mechanisms. This meant powder trains (burning fuse) which were inherently less accurate.

[Dandelion]

I believe it is all in the absorption of energy at the impact. Depending entirely on ground condition (capacity to absorb energy), everything bounces regardless of weight (real or relative) to some extent, at any angle of drop. One can try this out oneself by hurling rocks at the earth.

Never looked into the fuze mechanism of bouncing shells, I'm not an artilleryman (which explains why I am asking in the first place). I seem to recall that a tube of some kind was used in these things? Isn't there always a tube of some kind.

Anyway I hadn't imagined the existence of these shells to be a controversial issue. The three basic modes of detonation - penetration burst, surface burst and airburst (by timer or sensor or by bounce) were introduced at a very early stage of my military career. If I am not mistaken the only way to achieve penetration burst and bounced airburst is by delayed fuze.

So I just wanted to know the qualitative difference.

Why would a burning fuze be inherently inaccuarate? As I recall it the burning time of any material can be predicted with extreme accuracy - why not the same accuracy as the progression of a mechanical clockwork?

Yours

Dandelion

[JonS]

Originally posted by chiavarm:

</font><blockquote>quote:</font><hr />Originally posted by JonS:

Heh. Waddya know. That's my new thing for the day.

Here's something I wrote on VT back in CMBO daze

Do you kow if CM uses/simulates the timed fuse mentioned in your article for normal HE or would that still be condsidered VT? </font>

[JonS]

Originally posted by Dandelion:

I believe it is all in the absorption of energy at the impact. Depending entirely on ground condition (capacity to absorb energy), everything bounces regardless of weight (real or relative) to some extent, at any angle of drop. One can try this out oneself by hurling rocks at the earth.

I thought it was only the German mortar rounds that had this bouncing capability? Artillery comes in at too low an angle, I should think, to be able to get reliable results. Also, adjusting it would be a complete bitch.

Why would a burning fuze be inherently inaccuarate? As I recall it the burning time of any material can be predicted with extreme accuracy - why not the same accuracy as the progression of a mechanical clockwork?

In a theoretical sense you're probably right, but powder train fuzes have been out of fashion for the better part of 100 years now. There must be a reason for that. It could be due to practical limitations in setting a powder fuze compared to a MT fuze. It could also be a reliability issue - a powder fuze being more likely to fail than an MT fuze.

It should probably be borne in mind that MT fuzes aren't that great. Even now an ideal adjustment with MT fuzes has one bursting on the ground (i.e., the PD element trips before the MT bit does) to every two in the air. Mostly they get used for 'payload' rounds that don't require extreme accuracy - smoke, illum, and the like. Especially given the advantages of using VT fuzes for an airburst HE mission.

Jon

Edit: getting back to powder fuzes - one of the reasons the RA dropped shrapnel in WWI was that it was felt that learning the intricacies of the powder fuze then in use would be too costly and time consuming for the rapidly expanding number of new gunner officers to pick up. That may be indicative of another advamtage of MT over powder.

[ March 03, 2005, 07:27 PM: Message edited by: JonS ]

[flamingknives]

Originally posted by Dandelion:

I believe it is all in the absorption of energy at the impact. Depending entirely on ground condition (capacity to absorb energy), everything bounces regardless of weight (real or relative) to some extent, at any angle of drop. One can try this out oneself by hurling rocks at the earth.

Maybe, but try hurling aerodynamic, 12kg plus rocks at the earth or, failing that, ordinary rocks at mud. They don't bounce. Now try throwing rocks at hard surfaces. How often do they break?

Never looked into the fuze mechanism of bouncing shells, I'm not an artilleryman (which explains why I am asking in the first place). I seem to recall that a tube of some kind was used in these things? Isn't there always a tube of some kind.

AIUI, the 'bouncing' mortar bombs used a small point detonating explosive charge to launch the shell back into the air and start a delay fuse.

[qb

Anyway I hadn't imagined the existence of these shells to be a controversial issue. The three basic modes of detonation - penetration burst, surface burst and airburst (by timer or sensor or by bounce) were introduced at a very early stage of my military career. If I am not mistaken the only way to achieve penetration burst and bounced airburst is by delayed fuze.

So I just wanted to know the qualitative difference.

Why would a burning fuze be inherently inaccuarate? As I recall it the burning time of any material can be predicted with extreme accuracy - why not the same accuracy as the progression of a mechanical clockwork?

Yours

Dandelion [/QB]

mmm. Perhaps it was variability. Nonetheless, accurate packing of explosives (which effects the burn rate) can be messed up by bouncing a falling arty shell through 180 degrees. The delay-airbursts used by Sherman gunners were skipping the shell like a stone. The change in direction wasn't very great.

[Foreigner]

I might be wrong, but doesn't speed of burning depend on temperature and humidity, among other things? Plus, mass production processes inevitably introduce variability - in this case, not every fuse is the same even from the start.

[DrD]

And altitude.

[JonS]

Lots of interesting stuff in the quote below, including some corrections to what I wrote above.

The Use of Air Bursts for Moral and Lethal Effect

At El Alamein air burst H.E. had been in considerable demand for use against hostile batteries and troops in trenches or under light cover (see p.148). Now many were convinced of the value of air bursts for moral effect. A psychiatrist's report from the New Zealand Division proved that a large percentage of the men disliked the unheralded air burst, such as that of the high velocity 8.8 cm., more than anything else except perhaps the mortar.(20)

Unfortunately time fuzes were not easy to make and production had lapsed when shrapnel was abolished in 1935 (see p. 11). The gunnery problem presented by the use of a time fuze was considered too difficult to be mastered by citizen armies, and for the sake of simplicity H.E. shell were provided with impact fuzes only. When, therefore, in March, 1940, time fuzes were demanded, by the 1st Canadian Division for use with the 25 pr., some difficulty was experienced in getting production going. After trials at Larkhill in August, 1940, had shown that “any divisional artillery should be able to carry out air burst ranging accurately”, (21) it was decided – in October, 1940 to manufacture both a mechanical and a chemical (powder ring) type of fuze; but the usual difficulties and delays were encountered and it was not until the latter half of 1943 that the supply became really satisfactory. There were indeed still some who argued that H.E. with delay action bounce was better than time burst H.E., and it was not until October, 1943, that an official pronouncement was made in favour of the latter for use against troops in slit trenches.(22)

In the meantime the 3.7 in. H.A.A. gun was there to fill the breach. It was the high velocity and the time fuze of the H.A.A. shell, more than anything else perhaps, that was responsible for the growing popularity of this weapon in the ground role.

Notes:

Page 11: Shrapnel was deleted from the inventory in 1935 because while it’s long beaten zone was capable of inflicting great carnage on deep infantry columns, as infantry formations became more and more extended, and as field fortifications became the norm, it’s usefulness markedly declined.

Page 148: “Another outstanding feature of the El Alamein battles had been the extent of the enemy’s entrenchments, and this had led to a demand for time fuzes for use with air burst H.E. against troops in slit treches and under light cover, and against partly dug in anti-tank guns. Indeed opinion in the Eighth Army was now emphatically in favour of air burst H.E. as a lethal weapon, and a request was made for 15 per cent. Of all field and medium artillery ammunition to be time fuzed. (17)”

(17) War Diary, M.G.R.A., M.E.F., January 1943.

(20) Arty. Lessons, Eighth Army, El Alamein to Sousse, issued by M.G.R.A., M.E.F., on 9th August 1943.

(21) Report by C.R.A., 1 Canadian Div., 29th August 1940.

(22) R.A.T.M. No.9 of October 1943.

Pemberton, A.L. (1950). The development of artillery tactics and equipment. The War Office. Page 170.

There are a number of other references to powder ring time fuzes, nearly all of which refer to it’s inaccuracy of timing and unreliability. But, having said that, bear in mind the quote above. Despite those problems, it was still seen as a vastly superior solution to some tactical problems. The only other reference to mechanical time is with respect to A.A. fuzes. And of course VT solved many the problems when it was released for ground use late in 1944, although it wasn’t a complete panacea.

Jon

Oh, by the way, Pemberton gives the translation of V.T. as Variable Time.