HE Effectiveness

[RexMan]

British Army Operational Research Sections during WWII (summarized in WO 291/180)

Probability of a hit on first round, hull down static Tiger Ie sized target, assumed no error in line or range by crew.

Versus a Hull-Up static Target

6 pdr @ 500yrds…..100 percent chance of a First Round Hit (FRH: first round hit)

6 pdr @ 1000yrds…100 percent FRH

6 pdr @ 1500yrds…96 percent FRH

6 pdr @ 2000yrds…87 percent FRH

Versus a Hull-down static Target

6 pdr @ 500yrds…..85 percent FRH

6 pdr @ 1000yrds…43 percent FRH

6 pdr @ 1500yrds…22 percent FRH

6 pdr @ 2000yrds…14 percent FRH

This data is very revealing (even though it is more than likely for solid shot type AP rounds). It shows that height is a very strong factor in obtaining hits on 'vertical' targets.

The reader show note that this is for a known range. A major concern in battling antitank guns is knowing the range. They are very small and not only hard to spot, but very difficult to guage in size and exact position. Many times, especially when they are backdropped against woods/towns, they are nearly impossible to fix on.

[ July 07, 2005, 10:52 AM: Message edited by: RexMan ]

[JonS]

Back already lewis?

[RexMan]

Originally posted by jacobs_ladder2:

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

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

Many tank guns specifically designed for WWII (in the later years) purposely designed the HE rounds to have lower velocity than the AP round. In other words, they may not be expected to have as much accuracy as the Tiger I.

Accuracy is relative. Low velocity adds some advantages - particularly in terms of adjusting and terminal ballistics. </font>

[RexMan]

The US Army made quite a practice of using HE at long range from tanks in a indirect mode. They mention it at length in training manuals and German reports speak of great quantities of HE being used against them at maximum ranges.

Terrain, of course, could rule this out but given the opportunity, shermans would bombard ATG at great ranges.

The US tanks had gunner's quadrants it seems.

[flamingknives]

So?

In any case, JonS is right. Accuracy is not a function of velocity in any way shape or form.

Higher velocity helps to reduce ranging errors and cross wind effects, but does not improve the inherent dispersion of the gun.

Oh yes, hello Lewis. Stopping long?

[MikeyD]

I recall a report that a 75mm Sherman gun tanker hit a Panther square under the bow from 600m+ with a SMOKE shell! Those puppies just have 12% the muzzle energy of a AP round. That's an amazing bit of shooting.

A lot of the high velocity accuracy stats are skewed due to the use of sabot rounds which - if the pot separates badly in flight - can have horrible accuracy. Also high velocity guns tend to wear out their barrels faster, which ruins the rifling and increases dispersion, plus a HV weapon might lave a long tube gun which increases the likelyhood of barrel jump where the barrel literally flexes on firing. On the other side some of those smaller howitzers had VERY tight rifling, giving a round a hefty stabilizing spin on firing, despite the low velocity. But all things being equal, a flat fast trajectory *should* decrease round drop and dispersion.

[jacobs_ladder2]

Sorry if this is a little off topic, but the point concerning accuracy fits in with something I have been working on.

So, as the distance travelled increases the shell inevitably follows a flat trajectory. Just a few questions about this.

In longer range firing, are HE shells less effective against defensive works? Do you want a high-trajectory when hitting prepared defenses? If so, when firing at near minimum range, how much choice do gunners have over trajectory? Would you be able to choose a high or low trajectory depending on the type of target?

Cheers

Paul

[RexMan]

The US 75mm armed shermans did not fire a smoke round with 12% of the muzzle energy (do you mean velocity?) of any AP round they fired.

It is not quite the amazing feat that you imagine. I can get the actual muzzle velocities for all the US 75mm rounds if you like.

[MikeyD]

A couple years ago I looked up the 'muzzle energy' of particular 75mm/76mm gun rounds in Hunnicutt's Sherman. Usually measured in foot/tons. The HE (supercharge) was up there - some thing like 1 1/2 million (a VERY round number, I don't have my references at hand) foot/pounds. The much lighter HC smoke shell was a small fraction, something like 12%, if memory serves.

Yup, muzzle energy not muzzle velocity.

[RexMan]

Originally posted by flamingknives:

So?

In any case, JonS is right. Accuracy is not a function of velocity in any way shape or form.

Higher velocity helps to reduce ranging errors and cross wind effects, but does not improve the inherent dispersion of the gun.

Oh yes, hello Lewis. Stopping long?

You are probably confusing accuracy with something else as well as confusing the accuracy of hitting vertical targets vs. horizontal targets.

And as far as 'so?'. Can you care to expand on that? Or what you are 'soing' about?

[RexMan]

Originally posted by MikeyD:

A couple years ago I looked up the 'muzzle energy' of particular 75mm/76mm gun rounds in Hunnicutt's Sherman. Usually measured in foot/tons. The HE (supercharge) was up there - some thing like 1 1/2 million (a VERY round number, I don't have my references at hand) foot/pounds. The much lighter HC smoke shell was a small fraction, something like 12%, if memory serves.

Yup, muzzle energy not muzzle velocity.

Muzzle energy is easily calculated as 1/2*mass*velocity^2.

The sherman smoke shell is actually a HE shell filled with some type of smoke producing chemical and a small HE core. The mass is not that much different than a HE shell.

You are also incorrect regarding twist and spin. A higher velocity gun does not need an agressive twist to get the same amount of spin.

[ July 07, 2005, 03:04 PM: Message edited by: RexMan ]

[JonS]

Originally posted by jacobs_ladder2:

So, as the distance travelled increases the shell inevitably follows a flat trajectory.

Not necessarily, but anyway …

In longer range firing, are HE shells less effective against defensive works?

Less effective than some other kind of proj, or less effective than HE at short range? If you mean HE at short range the answer is ‘not really’. The HE round carries its own stored energy with it in the HE filling, and that energy isn’t released until the round explodes, be it at long or short range. Sort of like a HEAT rounds having the same armour penetration regardless of range.

The splinter pattern of the HE round is dramatically affected by its orientation on detonation, with vertical providing a more even, more circular, dispersion than horizontal. At longer ranges the round will tend to be coming in more vertically than at shorter (think of a parabola truncated by air-resistance – the first half of the traj is nearly the same as a parabola in a vacuum, as is the max height, but the distance travelled in the ‘downward’ half is much shorter, leading to a steeper impact), giving a better dispersion.

However, against defensive works that kind-of doesn’t matter. The dispersion really only matters against troops in the open, since a surprisingly small amount of cover is proof against artillery fragments. Fire against dug in troops requires direct hits (or very very close misses) to have any casualty-causing effect. Suppression still works fine against them though – so suppress the heck out of them, then send the grunts in

Do you want a high-trajectory when hitting prepared defenses?

It helps. The chances of penetrating the overhead cover are increased, as is the chance of getting lucky and dropping one in a pit, but as above the better dispersion pattern makes little difference against prepared defences.

Sidebar: in a moment of blonde-ness I read the previous question as ‘high-velocity’ rather than ‘high-trajectory’. As such, the following isn’t really relevant, but it may answer some other questions:

It depends what mechanism you’re trying to exploit. If you are trying to pierce the defences then yes HV is important, just like HV is crucial to KE A-Tk rounds. If you are relying on blast or fragmentation then it doesn’t matter as much.

Although, having said that … against ‘soft’ defences like earth berms or sand bags, you might use an HE round with the fuze set to ‘delay’. That means that the detonation chain won’t start until approx ?0.25? seconds after impact. That gives the HE round a chance to burrow in a bit before it explodes, increasing it’s effectiveness against dug in troops. Obviously the faster the round is going when it impacts, the further it will burrow before exploding.

If so, when firing at near minimum range, how much choice do gunners have over trajectory?

For any given range and MV there is a high angle and a low angle which can be used to reach a target. So that still gives us two trajectories. With guns or hows that use a variable charge bag system there is generally an overlap in the ranges at which each charge is to be used. For example, C1 might be for 0 – 2000m, C2 from 1000 – 3000m, C3 from 2000 to 4000m, etc. In that case, you might be able to use two, or more, different charges to achieve the given range, each of which will have a different traj (because of different MVs), and each of which can still use high or low angle.

Would you be able to choose a high or low trajectory depending on the type of target?

Yes.

Note that all of the above is kind-of theoretical. In practice most of the choices are made for the FO in the drills he uses, and the type of mission he engages in. To take one example; for any given range there is an optimum charge that will be used. Also, low angle is used by default so as to make the job of an enemy using locating radar harder. An FO could over-ride those, and order a particular charge or a different trajectory, but generally wouldn’t.

Finally, if you know what you are doing it is possible to take advantage of anything. So, the uneven dispersion of fragments from a round coming in at an angle can be taken advantage of by placing the rounds in a particular location, or high angle and a low charge might be used to ‘lob’ a round over an obstruction (like a hill or ridge) that would block a lower, faster round. Etc.

Regards

JonS

P.s. Oh, bear in mind I’m largely talking about indirect fire using artillery. Most of it still applies to other weapons though, particularly tanks firing HE indirect ‘in battery’. Except, of course, that they don’t have a variable charge bag system.

[RexMan]

And tanks generally do not have the elevation required to use upper register.

[JonS]

piss off lewis.

[RexMan]

..and much of that has nothing to do with hitting a vertical target like an antitank gun shield.

[flamingknives]

The US Army made quite a practice of using HE at long range from tanks in a indirect mode. They mention it at length in training manuals and German reports speak of great quantities of HE being used against them at maximum ranges.

Terrain, of course, could rule this out but given the opportunity, shermans would bombard ATG at great ranges.

The US tanks had gunner's quadrants it seems.

And your point regarding this being? It seems poorly placed with regards to the rest of the thread.

You are probably confusing accuracy with something else as well as confusing the accuracy of hitting vertical targets vs. horizontal targets.

No, I'm not. Accuracy is a measure of dispersion. There is no reason why a lower velocity gun cannot have less dispersion than a higher velocity one. What high velocity does is mitigate gunner errors and variable atmospheric effects.

Given data supplied in the US Ordnance catalogue, 1944, I get the M.E. of the 75mm smoke shell, the M64, as 25-40% of that of the AP shell. The AP shell will burn energy off faster, but it will also get to the target faster. As I don't have the variable drag coefficients to hand, I can't calculate energy at target.

[RexMan]

Poorly placed? Worse than your FlaK contribution?

[flamingknives]

At least that followed on from the previous post. The link was the attacking of exposed turret crew. It wasn't the latest thing I found off Google.

[RexMan]

Except you were assuming an exposed turret crew?

Could you also explain what this is about?

Given data supplied in the US Ordnance catalogue, 1944, I get the M.E. of the 75mm smoke shell, the M64, as 25-40% of that of the AP shell. The AP shell will burn energy off faster, but it will also get to the target faster. As I don't have the variable drag coefficients to hand, I can't calculate energy at target.

You just finished saying there is no correlation between accuracy and velocity (hah!) and now you want to calculate energy at target? Why?

[ July 07, 2005, 04:45 PM: Message edited by: RexMan ]

[RexMan]

Until people here can grasp the difference in vertical dispersion and horizontal dispersion, there is no point about discussing accuracy.

[jacobs_ladder2]

Originally posted by JonS:

</font><blockquote>quote:</font><hr />Originally posted by jacobs_ladder2:

So, as the distance travelled increases the shell inevitably follows a flat trajectory.

Not necessarily, but anyway …</font>

[flamingknives]

Originally posted by RexMan:

Except you were assuming an exposed turret crew?

Well, the preceeding post by Emrys was:

Unlikely that a detonation underneath the tank would kill men in the turret, even if you could get a riccochet fired from a lower elevation to pass beneath—which is itself a highly unlikely eventuality. Much more likely he is speaking of causing casualties to turret crew who have their hatches open and are exposed.

so it seemed germane.

Could you also explain what this is about?

</font><blockquote>quote:</font><hr /> Given data supplied in the US Ordnance catalogue, 1944, I get the M.E. of the 75mm smoke shell, the M64, as 25-40% of that of the AP shell. The AP shell will burn energy off faster, but it will also get to the target faster. As I don't have the variable drag coefficients to hand, I can't calculate energy at target.

You just finished saying there is no correlation between accuracy and velocity (hah!) and now you want to calculate energy at target? Why? </font>

[Michael Emrys]

Originally posted by jacobs_ladder2:

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

</font><blockquote>quote:</font><hr />Originally posted by jacobs_ladder2:

So, as the distance travelled increases the shell inevitably follows a flat trajectory.

Not necessarily, but anyway …</font>

[RexMan]

Do feel free to explain how a guns inherent accuracy is dependent on velocity (with higher velocity being more accurate). I'd like to see how you reason that.

Again, Unless a person understands that there is vertical dispersion and horizontal dispersion, there is no need to discuss accuracy.

You are throwing the word accuracy around without recognizing one of the most fundamntal aspects of this discussion.

As food for thought (for those that can eat) try to understand this..

An antitank gun is accurate when attacking tanks yet inaccurate when attacking a trench. Tank and trench are both at 500 meters.

[RexMan]

US tank gunnery indirect fire:

The reason I bring up the US tank gunnery emphasis on indirect fire techniques is because it may actually reveal something about the gun system itself.

If you have a small target like a 1 meter by 1 meter antitank gun at 3500 meters, thats a sub-mil target. It may actually be at the limit of aiming of the weapon. The actual fine corrections that can be dialed in is what I am speaking about. In technical terms this is called resolution. You actually must have even better resolution to adjust aim after initial aiming. Typically a factor of 10 would be good and a factor 0f 5 maybe acceptable.

In addition:

US tank gunnery policy for the 75mm ordered HE against tanks at ranges over 2000 meters. I am not so sure this is due to failure to penetrate as much as failure to actually hit the target. Surely a 75mm AP round can destroy many vehicles with a side hit at this range?

It is a branch off the discussion but still within cherry tree.