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4.2 inch mortar impact

khaba

Member
In my line of work (i'm a archeologist) we occasionally come across some ordnance. This time it was the tail and fuze of a 4.2 inch british mortar. As you can see in the photograph the fuze was found about 15 cm above the tail. My question: why are the fuze and tail found so close together and in this configuration? You would expect the tail to be blown skyhigh and miles away. It isn't just coincidence; they were found like this more than once.

I hope someone has the answer; i just can't figure it out.

greetings,

Alfred
 

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There are a thousand variables involved, all which can affect distribution of fragments. Ordnance R&D people have tried to perfect this since the first rock was thrown, its still far from a perfect science.

Even on a perfect R&D detonation there are many variables that affect fragment distribution, and in the field there is no such thing as a perfect detonation.

Angle of impact, terrain, depth the munition penetrates into the soil before detonation, munition type (HE, smoke, etc), all play a part. Additionally the fact that the tail is not part of the body and the construction features of the 4.2 means that it is less affected by the detonation than the body of the munition, forward momentum still plays a part.

Also, don't forget also that your tail does not necessarily come from this mortar. Mortars are not normally fired as a single unit, dozens, even hundreds may be fired at one time.

In addition you are looking at the site years later, not at a fresh crater. Items frequently roll downhill, are displaced by rain, etc. It's not unusual in steep, hilly areas to find groups of items in gullys at the bottoms of hills. The same goes if there has been activity in the area which has disturbed or displaced the soil like farming or armor activity.
 
Ofcourse, everything you say is true, but i'm pretty sure that fuze and tail belong to the same mortar. First of all, the type fuze is the right one for this mortar. And yes there were lots of these fired in the region (4000 over a frontline of 20 km) but this field (about 16 hectares) has been searched for ordnance and only 20 mortartails have been found (allthough obviously they missed at least one), at least a couple of them accompanied by their fuzes. And that brings me to the most important point; tail and fuze have more then once been found together. Like I said, i don't believe this to be coincidence.
Further, the layer where the items have been found have not been disturbed afterwards, and there are no significant differences in height in the terrain. As an archaeologist I can say that both the tail as the fuze were found in situ.


PS. Is a mortar specifically designed to direct the explosion sideways?
 
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You say that the layer has not been disturbed afterwards, does the layer show any evidence of disturbance from the original detonation?

Normally with a PD fuze about a third of the fragments (projo/mortar) can be found in the immediate vicinity of the crater. With this and the shape of the crater many of the old manuals tried to use the remnants to identify the munitions and the direction from which they were fired (crater/fragment analysis).

The fragments of a mortar are generally designed to go in all directions (360 degrees around the vertical axis), but this is affected somewhat by the thicker body construction at each of the ends and by the angle of impact with the ground.

There has to have been some disturbance since the time of detonation, as there is no evidence of the original crater following the detonation and the components are underground. IF the fuze and the tail belong together, then the remaining fragments must be nearby. Two isolated fragments do not end up together at that depth of soil with no crater and no other fragments, unless there has been some outside action in addition to the original detonation.

I can see weathering effect erasing some shallow craters, but the depth you have your fragments at is pretty significant for a mortar, especially the tail. You can still see trenches from WWI that have not weathered closed, to find limited pieces of a high explosive munition that deep with no evidence or remnants of a crater seems improbable.

I've included a couple of pages from a typical manual to give you an idea of what I am referring to in regard to the craters. Hope it helps.
 

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I can confirm it is not unusual to find 3 and 4.2 inch mortar remains like this, at work we regulary find tails and fuze close to each other,,most often in the opposite to your photo with the fuze been deepest and the tail on top ,
what i will add is the ones we find most commonly like this are 3inch phosphorous rounds,could this be the answer,phosphorous rounds using less of an explosive force, enough to burst and fragment the casing without spreading it over too large an area ?
 
There is a rule. 'What goes up must come down'. If the tail is blown vertically there must be a chance it could land near the main body. Is that too simple?

John
 
I can confirm it is not unusual to find 3 and 4.2 inch mortar remains like this, at work we regulary find tails and fuze close to each other,,most often in the opposite to your photo with the fuze been deepest and the tail on top ,
what i will add is the ones we find most commonly like this are 3inch phosphorous rounds,could this be the answer,phosphorous rounds using less of an explosive force, enough to burst and fragment the casing without spreading it over too large an area ?


I'd accept this, if you are finding the body nearby as well. For the US WP rounds the body is generally nearly in one piece, split down the side and frequently with the fins still attached. How do you normally find yours?
 
Or like this :tinysmile_hmm_t:
 

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@US-subs: The lack of a visible crater is another riddle. You can see a slight dip in the topsoil but that's all. I can imagine though that the lower part of a crater fills in fairly quickly by erosion of the surrounding soil which would possibly leave little traces. It makes you wonder how many of the older features (which we are actually looking for) are still visible. As there is no mixing between the topsoil and the underlaying layers, the crater or any later disturbance has filled in very quickly before any topsoil has flowed in with the rain (this being Holland in winter).
By the way, thanks for introducing me to the wonderful world of crater-analysis, I had no idea. Definitely something i will look into further.

The other replies make clear that we can rule out coincidence. Unfortunately i haven't looked for any other (body)fragments.
Is there a difference in the shape of the tail between smoke and HE rounds? The mortars in the image in this thread http://www.bocn.co.uk/vbforum/4-2-in...22.html?t=4022
seem to lack a small protruding bit on the outside of the fins, which HE mortars seem to have (and my mortartail has as well).
 
Most of the mortar remains we find on tasks are 3inch mortars,i have attatched some pics,the small poor quality pic shows how we normally find the remains of them,the circled areas are definately from phos rounds they tend to have a small nugget of the body still attatched where the tail screws on,with remains of phos trapped in the threads and on the nugget,again we tend to find the fuze about 12inches below the tail remains.we occasionally get ones as per MBs previous picture with a large proportion of the body still remaining ,The 4.2 again usually we have found tails only but again occasionally we get a fair sized chunk of the body,(this is when we find other bits of the fragmented body in the hole).
Sometimes we get a complete body split open as per the attatched photos.The average depth we find the them is 3 feet (36inches) but they have been found much deeper (see attached photo).The type of ground we work on finding these in the UK can be very soft (moorland) often showing no signs of cratering
 

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@US-subs: The lack of a visible crater is another riddle. You can see a slight dip in the topsoil but that's all. I can imagine though that the lower part of a crater fills in fairly quickly by erosion of the surrounding soil which would possibly leave little traces. It makes you wonder how many of the older features (which we are actually looking for) are still visible. As there is no mixing between the topsoil and the underlaying layers, the crater or any later disturbance has filled in very quickly before any topsoil has flowed in with the rain (this being Holland in winter).
By the way, thanks for introducing me to the wonderful world of crater-analysis, I had no idea. Definitely something i will look into further.

The other replies make clear that we can rule out coincidence. Unfortunately i haven't looked for any other (body)fragments.
Is there a difference in the shape of the tail between smoke and HE rounds? The mortars in the image in this thread http://www.bocn.co.uk/vbforum/4-2-in...22.html?t=4022
seem to lack a small protruding bit on the outside of the fins, which HE mortars seem to have (and my mortartail has as well).

For the UK 4.2-inch there is a hex nut at the junction of the body and the tail for the smoke and CW rounds. For the HE round the nut is absent.
 
Here is the best picture I can find at the moment. This is one that was intended for fill with CW agent, the WP smoke is the same body.
 

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Found another. These were CW filled, found at the same site identified in another thread currently running. You can see the hex nut in the example on the left.
 
And here they are with a picture this time.
 

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Mortar bomb tail units

Interesting thread. The 4.2 inch bombs I find are generally in one (body ruptured) or two (top half ripped from lower half) pieces. Those I find have the hexagon nut below the body, as explained by US-Subs. usually the tail unit is still attached.
 

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Attached a few shots showing impact of empty rounds that were fired since it will give you an idea of what a live round would have looked like at point of impact. The depth of penetration would be a factor of ground density so wet sandy soil or an area that had already been brewed up would likely have placed the rounds completely underground when they went off.

Two each showing 2-inch and 4.2-inch are attached. Can't find any shots of the 3-inch for comparison but found one where we had set up the tube so not sure where they went. My spotter seen in the photo was responsible for locating rounds and taking photos of interest. :egg:

Both types of 2-inch tail unit are shown and the ones on the 4.2-inch rounds are the postwar pattern.
 

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I can tell you from my experiences overseas with the military that it is normal to find the fins close to the point of impact and sometimes laying in the splash mark even on hard ground (ie: impact on an asphalt road). We did some basic training on how to determine the location from where a mortar was fired based on the splash mark left on the ground. We were taught that mortar bombs will leave a splash mark that is larger on the side that faces the direction that the bomb was fired from and that artillery splashes are larger in the direction of travel. Also, when a mortar explodes the force of the explosion is predominately sideways and not towards the fuze and tail which explains why the tail is free to simply fall to the ground after the body explodes rather than being thrown back into the air. I've been in buildings that have had mortar impacts to the roofs and most of the time we would find the fins directly below the hole in the roof.
 
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Thanks everybody for your reactions. Something that on first sight seemed to be very improbable is apparently more a rule than a exception.
 
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