Modelling the effects of HE on armour

[Whirlwind]

This question was inspired by reading an argument on Twitter about Boxer: whether the benefits it brought were so important as to require their use on command and ambulance vehicles as well as IFVs designed to be in the direct fire zone.  Anyway, ignoring the real life procurement issues, that got me thinking about how different rules model the effects of different sizes of barrage and shells on a range of armoured vehicles.  I’m not thinking of direct hits with HE weapons, but the effects of blast and fragmentation.

[Jim Webster]

I think the question has to be how much HE and how thick is the armour. At one extreme you get the account of tanks rolled over by naval gun fire in the fighting during the breakout from the Normandy beaches. On the other hand you had tank crews who would call down artillery on their own position if they were in danger of being overrun by enemy infantry

https://jimssfnovelsandwargamerules.wordpress.com/

[Not Connard Sage]

Jim Webster wrote:

On the other hand you had tank crews who would call down artillery on their own position if they were in danger of being overrun by enemy infantry

Did that ever happen? Besides the chances of a direct hit spoiling someone’s day, a mobility kill was a probability. Withdraw firing would be my choice, (bounding overwatch).

Obvious contrarian and passive aggressive old prat, who is taken far too seriously by some and not seriously enough by others.

[Jim Webster]

I was never there so cannot vouch for it 🙂

In Caen, Anvil of Victory there is an account of tank crews calling down artillery, assuming they’d get 25pds but getting heavier instead which was a bit unnerving.

But even troops who weren’t in tanks could do it. To quote from https://www.nam.ac.uk/explore/battle-imjin

By now the entire Chinese 63rd Corps was across the river and threatening to entrap the other battalions. But still the Fusiliers, Glosters and Ulster Riflemen clung on, repelling attack after attack. When the weight of the enemy assaults seemed overwhelming, they even directed their own artillery fire on to their positions.

Also in Korea
Yet again the Centurions had proven themselves to be
effective in combat, and were demonstrably resistant to almost
any munitions the enemy could bring to bear against them. This
was true even all the way up to 155 millimetre artillery
shells, which Centurions reportedly took direct hits from
without suffering any more than ‘superficial damage’. In
fact, the level of resistance to artillery boasted by the
Centurion was so high that when swarmed by the Chinese, as
well as spraying machine-gun fire over each-other’s hulls,
Centurion crews would sometimes even call in artillery fire on
their own positions

https://www.sahr.org.uk/docs/kingsleyfilshie_schools_winner_sahrs1043.pdf

I suspect that it was something done when you couldn’t go backwards and the alternative was far worse

https://jimssfnovelsandwargamerules.wordpress.com/

[MartinR]

For WW2 type artillery, I think the general rule of thumb was for light artillery (75mm or less) fully enclosed AFVs had little to worry about apart from incidental damage from shell splinters.

For field guns, (25pdr, 105mm and up) there was a chance of vehicles being disabled due to tracks damage. Direct hits would demolish lightly armoured vehicles.

Medium guns (150mm and up) were quite dangerous, even for heavily armoured vehicles, with a significant chance of disabling them if they hung around in the beaten zone. Direct hits from 150mm HE will destroy almost anything except heavily concreted fortifications , which is why even modern artillery crews aren’t issued AP rounds.

I’m sure there are exceptions of course, and it depends on the velocity of the rounds which may explain the Centurion example above. Not sure I’d want to be in an armoured box with a 155mm shell going off on it. They have a Lot of explosive in them. I did read of a Churchill which took a direct hit from an 81mm mortar, the tank was undamaged, but eas disabled for a while as the crew were blinded by all the dust blown out the cracks inside the tank.

I always liked the approach in the old WRG rules to area fire, very simple, but effective.

"Mistakes in the initial deployment cannot be rectified" - Helmuth von Moltke

[deephorse]

Jim Webster wrote:

In Caen, Anvil of Victory there is an account of tank crews calling down artillery, assuming they’d get 25pds but getting heavier instead which was a bit unnerving.

Did this happen?  Could this happen?  There’s a little thing called ‘radio nets’ which makes me think that this is highly unlikely.  If individual tank crews could call in their own artillery, why did they bother putting FOOs in specially equipped tanks in order to do just the same job?

It is just conceivable that a fire request was sent up the chain by an individual tank crew, or that a FOO was close enough to the action to request it himself, but an individual tank is not going to be part of the artillery’s radio net.

Play is what makes life bearable - Michael Rosen

[Jim Webster]

As I said, I wasn’t there, but the author I quoted, Alexander McKee. served with the London Scottish and the Gordon Highlanders regiments during World War II. He served as part of the British Army of the Rhine (BAOR) during the occupation from 1945.

 

I’m happy enough to follow him in this

https://jimssfnovelsandwargamerules.wordpress.com/

[John D Salt]

Off the top of my shiny head, I think there are three mechanisms one can usefully distinguish of how HE shell will damage AFVs.

The first is penetration of the armour by an intact shell, similarly to AP shot. This obviously can only happen if the fuze has a delay long enough to permit penetration to happen. A method used by 25-pounder gunners before proper AP shot became available was not to fit a fuze at all, but fire HE with the travel plug in the fuze well. Probably this would be less effective than proper AP because the filling space makes the shell weaker, but I have never seen any information quantifying the difference.

The second penetration of the armour by shell fragments. Some WW2 OR documents I have seen show the “vulnerable area” (what we would now call mean area of effect) of different shell against thin mild steel plate from a quarter of an inch upward. The annoying thing for wargamers is that the most effective fragmentation pattern against personnel — lots and lots of teensy tiny fragments, such as produced by Soviet 82mm cast iron mortar bombs — is pretty worthless against armour, and fewer, bigger fragments are wanted. I understand that its big-chunk fragmentation pattern was one reason (along with a couple of thousand yards more range) for retaining the 4.5-inch gun for counter-battery work when the 5.5-inch with 80lb shell would otherwise have been a better bet.

The third mechanism is blast, and, as usual, air blast is a disappointingly ineffective method of damaging people or things, and is not at all likely to hurt armour plate. What it is more likely to do is to damage or destroy fastenings between plates, fracturing bolts or rivets or opening up weld seams. Sufficient blast — the sort of thing from aerial bombs rather than field artillery — might be sufficent to knock turrets off, flip vehicles over, or from subterranean detonations excavate craters vehicles can fall in to (fougasse effect). WW2 OR docs I have seen suggest that incendiary effects from aerial bombs play a greater-than-expected part in damaging AFV.

A lot of wargames rules only distinguish alive and dead states for AFV, but for a more detailed treatment one might include external systems damage, quite likely to be produced by blast or fragments — antennas stripped off, vision blocks fractured, and for the modern period externally-mounted missile or sensor systems getting bent.

Patton’s battle notes include the assertion that medium tanks can advance safely under friendly time fire (that is, airbursts), and in this regard it is perhaps worth mentioning that the Sherman had better roof armour than most other tanks. I’ve also seen OR docs reporting a live fire experiment in which a Churchill squadron drove through a live fire concentration of 25-pounder airburst (twice). Direct hits were recorded as being not at all uncomfortable; the exercise resulted in one crew casualty, which sounds as if it might have been quite nasty from the remark that it would not have occurred with the new kind of direct-vision optic. IIRC one vehicle was immobilised.

There is one incident I recall from some tank commander’s memoirs — 64 Days of a Normandy Summer, By Tank Into Normandy? — where a Cromwell survives a direct hit from a 15cm Nebelwerfer. In principle that’s a big enough calibre to be effective, but AIUI the only fuze option available was superquick (US instantaneous), so the thing bursts ineffectively before it has a chance to penetrate. A good idea not to have your head out of the turret at the time, though.

IIRC the US Army rule of thumb for a long time was that tanks should expect 1% casualties per salvo of 155mm HE, but Gulf War experience has suggested to some redlegs that the rate is rather higher.

Finally, there’s the “try to be incredibly lucky” method, exemplified by the Israeli para in the 1967 Sinai campaign who knocked out an IS-3 by posting a rifle grenade through an open turret hatch.

All the best,

John.

[Thuseld]

This thread has been full of fascinating information. Thank you all.

Experiments here: http://inexperiencedmodelmaker.blogspot.co.uk/

Tranquil Stars updates: https://tranquilstars.wordpress.com

[MartinR]

We mustn’t forget the Tiger II knocked out in Oosterbeek by a 3″ mortar bomb which landed on the engine deck and set the thing on fire.

"Mistakes in the initial deployment cannot be rectified" - Helmuth von Moltke

[Whirlwind]

Many thanks for all the interesting replies.

[John D Salt]

For what it’s worth, I dusted off my spreadsheet containing the Soviet artillery norms given in Lebedev’s Справочник офицера наземной артиллерии (“Ground artillery officer’s handbook”, Voenizdat, Moscow, 1984).

These are for indirect fire missions. No norms are given for attacking tank targets, so presumably the Sovs felt that such a thing would be fruitless. I imagine this is because the target would move before the norm could be fired — “moving target” is almost as good a way to taunt gunners as “crest restrictions”. I think it was Jim Storr’s “Battlegroup” that offered the insight that artillery makes infantry halt, but makes armour move.

What it does give are the neutralisation (25% casualties) norms for attacking artillery batteries, with separate lines for a battery in the open, a battery dug-in, or an SP battery. Norms are given for tube artillery from 76mm to 203mm calibre, mortars from 76mm to 240mm, and three different kinds of artillery rocket, labelled medium, medium long range, and heavy. My guess would be that these correspond to 140mm, 122mm and 240mm repectively, but it’s not obvious.

Being an SP battery offers better protection than being dug-in. It takes between 2 and 5 times as many rounds to neutralise a dug-in battery than one in the open, an average over all types and calibres of 2.82. Mortars seem more sensitive to dug-in targets than tube arty, and rockets very slightly less. Against an SP battery it needs between 4 and 6 times as many rounds as a towed battery in the open, the average over all types and calibres being 4.18. Again, mortars seem more sensitive than tube arty, and rockets very slightly less.

Contrary to what I would expect, for tube arty and mortars the large calibres seem to be rather more affected than small calibres against dug-in or SP targets. This may be a genuine effect, or it may be working on the assumption that all shells are fuzed superquick (instantaneous), which would be the default fuze for most field artillery work, but would not bring out the advantages of cratering power in the larger calibres.

As a general caveat, all the norms are obviously rough to the extent that numbers are typically rounded off to the nearest 10, so one should not treat any of these numbers as being especially precise. What’s more, no allowance is made for any difference between (in Russian terms) F, OF and O shells. For the sake of single rule-of-thumb multipliers, and reflecting the common calibres of 120mm mortars amd 122m gun-howitzers, it would be a pretty good approximation to say you need 2.5 times as many shells against a dug-in battery, and 5 times as many against an SP battery.

Artillery is, we know from WW2 British OR work, quite a hard target, so I also compared the norms for infantry in the open or dug in. These are, in broad hand-wavy terms, about 10 for tube artillery, 15 for mortars, and 30 for rockets — infantry seem to benefit from being dug-in much more than artillery does. When both are dug-in, it needs on average about 30% more shells to neutralise artillery, if it is fair to compare a battery as a target with a hectare of infantry.

Bearing in mind always the very loose, approximate, imprecise and wibblesome nature of these numbers, if we compare the difference for SP arty and troops in the open, the infanteers are about 20 times more vulnerable than SPs to tube artillery, 35 times to mortars, and 50 times to rockets. Presumably the multiples for tanks should if anything be a bit higher.

All the best,

John.

[Whirlwind]

Thanks for that John.  What initially piqued my interest in the Twitter exchange was wondering about the marginal value of increased armour for vehicles that aren’t expected to get hit by direct fire but might well get hit by indirect HE fire.  The sense from the above data is that armour beats not having armour by tons, and then there is a pretty small incremental value from increased up-armouring after that, (a very different curve to direct fire effects).

John D Salt wrote:

I think it was Jim Storr’s “Battlegroup” that offered the insight that artillery makes infantry halt, but makes armour move.

Quite.

[Brian Handley]

In the book Tank commander the author noted that their approach to tigers was to shoot HE at them and keep poring it in.   As the Shermans were never alone and had a high rate of fire it drove the Tiger off pretty much undamaged but then they would call something up that would get rid of it.

In tigers in combat they list Tigers lost to artillery.  However they were badly used for instance being told to guard a position all night.  Now Tigers do not have big fuel tanks so in the end it will have to stop so making it a good target for very concentrated fire, far more than it would ever meet in a moving battle.

Have we included the first conditions in Maneouvre Group?  No its too specific for the general but it would be easy to make such a rule up for that specific situation, but I would not want to extrapolate it to any other vehicle combination.

 

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