Cloche observatoire par éléments type 1 ou 2

Dernière modification par jolasjm le 20/01/2021.
Hello Michal

Thanks for your message and question which will allow us to improve on the precision and clarity of this page. The figures given initially in this page are targets that were given as specification for the cloche development and not actual possibilities for this cuirassement. The actual firing angles and observation are not mentioned in the documents that I've been able to read about them, ... and probably a bit random !

The factual things : the creneaux were using adaptations of the standard GFM creneau cylinder so as to allow use of the Mo50mm mortar and GFM creneaux optics. The FM was forbidden because of lack of space (mentioned in the page).

Now a bit of extrapolation
- When it is about firing :
FM being prohibited because of the lack of room space inside, this was of course making its specific ball joint totally useless in such a cloche. The idea was in fact to use - with a widely opened creneau - either a simple handgun, rifle or a "pistolet mitrailleur" (submachine gun or PM), which is a much compacter weapon. Pistolet-mitrailleurs were in use in the french army since 1924 and - for information although out of subject - the GFM cloches were in fact initially meant to use "pistolet mitrailleurs" and not FM in their early stages of developments in the late 20's. In the same idea, I did read a few documents saying that PM could actually be used in VDP cloches.

For more information on PM that were used at that time :
http://armesfrancaises.free.fr/PM%20STA%201924.html
A new PM model was developed in 1935 and produced starting in 1938, but I'm not sure about its use in the Maginot line.

This is of course totally sub-optimal compared to the CORF standards, but probably acceptable in high mountain works, which were in essence of suboptimal CORF standard built by MOM. This kind of ad-hoc firing method is maybe the reason why the maximum negative firing angle was not mentioned in the documents, because this was depending on the weapon used in the créneau. A simple pistol or a rifle or a PM would give a rather variable maximum angle depending on the guy behind the weapon... and in this case much more limited by the top angle of the block concrete slab and terrain than by the creneau itself.

- Observation :
The "type S" GFM créneau do allow -70% observation although its firing range is limited to -50% (confirmed by SMF in a 1935 note to the Alps military engineering directions). This was actually implemented here or there : the la Dea cloche was designed with two "B" creneaux (modified "S") and the concrete slope of the block slab was calculated to allow -70% (-35°) observation . This was possible because of the specific machining of the lower surface of the "S" creneau. Here, with a much thiner armor than a GFM cloche, I would expect that this is possible as well. Just bear in mind that the external vision slit and mirror of the episcope is slightly above and in front of the horizontal axis of the episcope, allowing a good negative angle, probably higher than the one shown on your cloche slice.

Would you allow the reproduction of your two documents in the "Cloche Observatoire par éléments" page ?

Best regards
Jean-Michel

Hello Jean-Michel

Thank you for your notices and explanations. I’ll send you new versions of the documents.

And what about producers / factories? We have 8 bells of type 2, it’s a quite little number. But I see two or three producers I think:
Factory N° 1 – Arrondaz, Plate Lombarde, Serre la Plate, Col du Fort, Sainte Agnes
Factory N° 2 – Col de Granon, Col d’Agnon
And maybe factory N° 3 – les Rochilles (very thin pins)

Other possible allocation: Les Rochilles and Col de Granon have a trace along the welding between cylinder and cap.

And a question for number of parts of the bell. I can see: cap, cylinder, ring, inner coat (doublage). Second possibility: cap with cylinder (1 part), ring, inner coat. But only the cylinder without cap has weight about 3200 kg (raw calculation). Or are there another joints on the cylinder?

Best regards
Michal

Dernière modification par jolasjm le 21/01/2021.
Hello Michal,

Your question about producers/factories is a very good one :-). This is a point that could be added on this cloche page. I did check in my records if there are some indications. This is what I've found :

- There is in fact only one unique company that did supply these cloches : les Usines et Aciéries de Feignies (north of France).
- But there are two contracts to this company, fairly split in dates :
* the first one, dated 14/03/1935, covers 11 cloches.
* the second one, dated early 1939 is covering 3 cloches planned for the Col de Granon, Buffère and Col de Vallette ouvrages (the last one's construction was only barely started in 1940). Ganon was installed but Buffère (B3) and Vallette not.
* Documents do mention the existence in this contract of two prototypes - probably one for both "cloche par éléments" types (1 and 2).
* and last but not least, it appears that the mounting method has been changed in between. The initial method was based on aluminothermic welding, replaced at a later stage by threading and conventional welding (aluminothermy is a rather technical and complex method although giving incredibly good results. Difficult to apply in a MOM context, lack of specialists and high altitude). Drawings for the new "screwing" method are dated March 1937, which gives an ordre of idea for the date of change.
* there might have been sub-contracting which could explain other differences, but I don't believe much in this hypothesis : its a very small contract which do not deserve subcontracting...

So, there is only one supplier, but two contracts, a couple of prototypes (one type 2 and the unique type 1 at Pic de Garuche), and two mounting methods. The very thin pins at Rochilles are not relevant to me, as these pins may have been also existing on the other ones (except Granon and Agnon) but simply cut and grinded after installation.

Out of these 14 ordered cloches, only 10 were installed (1 type 1, 9 type 2) and two were planned to be installed. This means that in the first contract, 2 cloches were not having any destination : maybe the prototypes, or test cloches stored somewhere ? Of course there are still unknowns in this particular story, which are requiring a deeper investigation.

There are 6 main pieces in a type 2 cloche (4 slices for the main part, the casing as for the other cloches, and the doublage). The 4 pieces of the main part are : Upper dome (cap), upper part of the cyclinder (where the creneaux are) and two lower sections of this same cylinder, hidden in the concrete and behind the doubling. The 3 cylindric sections are more or less 500 mm high.

I have somewhere an interim drawing of this cloche done by SMF during project phase. I'll try to put it on line.
For the rest, we need to go back to the relevant archives ;-)

Best regards
Jean-Michel