Regelbau 671, HKB Thyborøn (4/HKAR 180)

[Lars Bertelsen]

Hello
The gun sight of a Sockellafette IV was placed at the right side of the gun, and a normal Regelbau 671 therefore has an aiming slit in the right side of the embrasure.
But the four R671s in HKB Thyborøn has got aiming slits in both sides of the embrasure. Anybody who knows the reason for this?
(photo: yesterdaysfoto.dk)
Lars

[jopaerya]

Don't have a reason but in the Sector Gironde , you can see this also . Sometimes these bunker are called 671 d .

[kstdk]

Hello

The bunkers are buildt in the spring 1944, and the guns there were from the start in 1940 - 4 pcs. 10,5 cm le.FH 18 and later in june 1941 it was 4 pcs. 10,5 cm. K331 (f).

Maybe - at the time the bunkers was buildt in the spring of 1944 - there were plans for some new guns, but not confirmed at the time - therefore they were buildt so they could be used with different types of guns? Just a thought

Regards
Kurt
kstdk

[Lars Bertelsen]

Hello
@ Jos: yes you are right about the R671d, but AFAIK this type was used for naval guns only, not for SKL-IV.
@ Kurt: I have thought of that too, but on the other hand, the gun sight of the SKL-IV is always placed at the right side of the Sockellafette, regardless of the type of gun installed.
First, I thought that the extra slits in the R671 at Thyborøn were made “by mistake” (but in that case, one might expect that the slits in the left side of the embrasures would have been filled with concrete afterwards). But then in Chazette’s book “Batteries de cote serie 600” I found a couple of photos of other R671s with slits in both sides of the embrasure (3./1252, 1./1254, 4./1254, and one unknown battery). It seems unlikely, that so many “twin slits” were made by mistake.
Maybe the extra slits in these R671s were made to obtain an extended arc of fire for direct shooting at short ranges at a low elevation??
Greetings Lars

[kstdk]

Hello

I just notised that the BFM mentions for the 671 at Thyborøn 1 pcs. 671 Gesch. Sch. Std. - but the other 3 is called 671 Gesch.Sch.Std. 120 grad.

Does all 4 have slits on both sides, or could it have to do with extended width of fire (80 - 120 degrees)??

Regards
Kurt
kstdk

[TH]

All four have slits on both sides.

Increased horizontal range was also my first idea. Assuming that is a reasonable explanation, it raises the question of why the extra range was necessary at Thyborøn and not at other places as well.

[Lars Bertelsen]

Hello TH
Hard to say. Seems to be some kind of ad-hoc solution, since the “twin slits” were not part of the standard layout of the R671 for a Sockellafette IV.
The attached photo (from Chazette’s “Batteries de cote serie 600”) shows two R671s in HKB Sainte-Adresse. The left bunker has got two slits and the right one only one.
Lars

[der bunkermann]

Hi, i was told it was to put the barrel when the gun is in "rest".
So it wont be sticking out, and be in the way for the camouflage nets or panels..

But i cant confirm that with any document.

[jopaerya]

I know I have a document about this but where ????????????

@ Lars also H.K.B. 3./1282 at Gironde had these "twin slits" see the drawing of Dirk

Beside the ones showed also the naval 671 at Raversijde has two slits .

[Natter]

This question was discussed in the norwegian kystfort-forum in 2008. According to JEF, the purpose of the slits were to allow the use of the gun's horisontal optical sight within the full fire sector (sights may have been mounted on either/both sides, hence the variation).

[Lars Bertelsen]

Thanks all for the answers.
Interesting case. Until last week I thought that the gunbunkers in Thyborøn were unique
Lars

[Natter]

This question was discussed in the norwegian kystfort-forum in 2008. According to JEF, the purpose of the slits were to allow the use of the gun's horisontal optical sight within the full fire sector (sights may have been mounted on either/both sides, hence the variation).

Same principle illustrated on a post-WW2 norwegian casematte:

[dirk Peeters]

that s nice natter
Dirk

[Lars Bertelsen]

Same principle illustrated on a post-WW2 norwegian casematte:

yes that slit is for sure for the gun sight only, not for the barrel.
It looks quite different than the cut-out in the right side of the embrasure of a normal R671. Maybe the cut-out in the R671 was a dual-purpose one?? Otherwise it seems strange that the cut-out is so high and always present to the right.
In the booklet “Die Regelbauten des Heeres im Atlantikwall” by Harry Lippmann (DAWA/IBA-Sonderheft 10) there is a copy of an original German drawing of a gun bunker with the text “Optikschlitz” beside the cut-out in the side of the embrasure.
I cannot find my copy of that booklet. Could anybody please post a copy of this particular drawing?
greetings Lars

[S_haule]

Dear Lars,

I think it's drawing extracted from a booklet with Regelbauten drawings published by Inspekteur der Landesbefestigung beim Oberbefehlshaber West.
Here the drawing of Regelbauten 670 and 671 from Nederlands Instituut voor Militaire Historie (NIMH) archives (Bureau Inlichtingen/ Duitse verdedigingswerken : 575-serie).

Best regards from Normandy,

Sébastien Haule