Ringstand/Tobruk - a question about construction elements

[Eugenius]

Hi guys, I'm a novice here, so I'm sorry if my question was already replied earlier. Here are some pictures of Ringstand located at 59.77091, 30.22428 - a part of field fortifications built most likely in 1942 - 43 south of Leningrad/St. Petersburg:

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A question: what is the purpose of rectangular openings/niches under the roof? They are ca. 30 - 40 cm deep, partly filled with concrete crumbs, no any traces of wood was found inside. Openings are located in the upper part of only shelter, not fighting casemate. Generally it looks like the roof is placed on rectangular columns. You may see through the openings on corners:

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The same openings are on another Ringstand in that area (59.78214, 30.22277):

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Was it just a result of concrete deficit? Or an attempt to create a kind of shock-absorbing layer of wood or sand inside roof slab for better protection of the pillbox? Any other options?

Many thanks in advance for your comments.

[Private Drew]

Those definitely don't look like they were a construction "accident", but rather look planned. Perhaps a window?

[TH]

I don't know, perhaps slits for observation or signaling? If the openings cut through the entire wall, that is.

[herring]

Looks like observation slots made in purpose.In Kreta I've seen a Tobruk with similar window (Platanias hill).
A ceiling is weakened definitelly - which anyway looks very thin. I doubt if it makes a sense.

Have you been inside, to check if it's possible to make observation?

Leningrad Tobruks seem to be an early ones, interesting if it was a free interpretation of the instruction, or strict following of unknown instruction.

[Eugenius]

"Perhaps a window?" - definitely not as those openings lie between roof and ceiling, there are no any "windows" inside the pillbox. Here are the pictures - shelter seen from the entrance:

Shelter seen from combat casemate:

Combat casemate:

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Note that this is no any anti-chipping protection (or what is the correct term for that?) of the ceiling.

We discuss this in our local forum either and the main suggestion is it was an attempt to increase pillbox protection against mortar mines - to arrange a layer of wood or sand inside concrete roof for that layer to act as a kind of shock-absorber. But the strange thing is those openings are only 30 - 40 cm deep, which is more or less equal to wall thickness, so wood- or sand-filled niches did not protect the most of the roof. it looks like the roof was placed on columns/poles. Another notable thing is there are no such openings on combat casemate, only on shelter part.

"Leningrad Tobruks seem to be an early ones, interesting if it was a free interpretation of the instruction, or strict following of unknown instruction" - those Tobruks were built in 1942 - 43, when the Wehrmacht ceased trying to assault Leningrad and focused on the siege instead, so a kind of trench warfare began. Those are examples of field fortification built with limited resources and in severe environment, so they are not "ideally modelled Ringstand", but rather something "looking like Ringstand" bunkers widely modified depending on available resources, landscape, builders' skills etc. I saw quite a number of German bunkers around St. Petersburg, but I can't recall any other built with such openings except on those two I saw recently.

[jopaerya]

Could it be a extra concrete protection for the Tobruk from hits on the top, like on the U boots bunkers ???

[Eugenius]

"Could it be a extra concrete protection for the Tobruk from hits on the top, like on the U boots bunkers ???" - actually this is the last idea came to my mind. Probably initial roof protection was considered to be too weak, so it was decided to add additional protection in the form of additional roof on poles.

I hope I will make another trip to that Ringstand before winter to explore those openings/niches in detail.

[dirk Peeters]

this seems very interesting
do you have a plan with measurements of that bunker ?
or could you measure a few things
is it a VF 8 or a BF 58c
the difference between them is next to the door to the gunpit it is 30 cm or 45 cm ?
also thickness of the roof before the strange openings
the roof is 40 cm or 65 cm for a reinforced one but here it seems 40 cm in one picture plus another layer of concrete
a thought could it be wood installed that has rotted and so fell out of the holes ?

[Eugenius]

"do you have a plan with measurements of that bunker ?" - not yet, but I will take a tape-measure with me when I go there again.

"is it a VF 8 or a BF 58c" - I do not think it is any exact Regelbau model. It is a classic piece of field fortification built quite roughly if to compare with similar objects in Europe.

"next to the door to the gunpit it is 30 cm or 45 cm ?" - could you please make it more clear? Actually there are no any doors there.

"could it be wood installed that has rotted and so fell out of the holes ?" - theoretically it could be, but I found no any trace of wood there.

The object is located on the outer side of anti-tank ditch spanning the area between two small rivers, the entrance is from south-west side:

A couple of more pictures from outside:

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[dirk Peeters]

next the door or dooropening
see the red circle please
VF8 30 cm

Bf 58c 45 cm

it would be a big help that you ll try to measure them
Thanks a lot in advance
Dirk

[Eugenius]

"see the red circle please" - OK, now it's clear, thanks. I would say the object we discuss is much similar to your drawing of VF 8 - generally rectangular shape and only one step between shelter and combat casemate. However, I do not think it might be attributed to any exact Bauform. But I will anyway measure the part you asked.

[dirk Peeters]

thanks a lot

[forttravel]

Hello Eugenius,
that strange detail in construction of Tobruk style bunker was noted by Soviet Engineers.
See my post #28 here: viewtopic.php?f=70&t=93178&hilit=armament&start=15

[Eugenius]

Hi forttravel, and many thanks for your valuable info. It is marked on the drawing you referred to that those niches were filled with "sand" (Песок). However, there was no any trace of armoured cover (бронекрышка) supports shown below on the same drawing with regard to the bunker we discuss, but I think that's because every pillbox was different from other similar objects - Soviet military engineers just marked most specific features of bunkers they explored. Another difference is that the niches on your drawing are shown also on the side of combat casemate, which is not the case with bunker I saw. I thought this - niches were made only in shelter, not in fighting casemate - was made on purpose, but probably not.

So It got clear with what those niches were filled with, but at least two things are still unclear: 1) what was the purpose of those niches and 2) how the builders managed to keep sand inside the niches? Were they covered with thin layer of concrete outside or what?

May I ask you about the source of your drawing? May I post it in our local fortification fans forum?

[forttravel]

Source of that drawing is: Альбом чертежей фортификационных сооружений немецкой обороны to download here: https://reibert.info/media/albums/albom ... 38/?page=2
Go ahead!