Reply To: Modelling the effects of HE on armour

[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.