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Post Info TOPIC: Mark IV - Periscope blocks or drilled plates?
MRG


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Mark IV - Periscope blocks or drilled plates?
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Maybe you are right and the blocks were replaced for plates at a later time because maybe they also ran full of water and dirt?

Of course glass splinters from shattered mirrors could also have been an issue - but still I would not like my eyes pressed against simple holes whith all sorts of stuff flying around.

Hmm, "Cynic" is still my favourite for making. It would also give me justification for work on a functioning mechanism for throwing off that fascine. smile

Sadly there's only that picture from the front which I found so far, but that shows the style of the name quite clearly. It was number 2731, call sign changed from C23 to C22 for the last deployment. On the picture where it sits on the rail carriage, with the fascine on top, it was probably C22.

No idea who the manufacturer was, though.

Luckily there's a lot of other pictures of tanks from C battalion, so I believe it would have had the ace-of-spades card on the sponsons and rear armour, together with the call sign on roof, sides and petrol tank armour plate, like Conqueror, Chaperon, Coquettell and Cherubim had.

Please someone correct me if I am wrong with sporting that card..



-- Edited by MRG on Tuesday 19th of February 2013 10:34:48 PM

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MRG


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Hello,

here I am again with another odd question. (Oh no!) It's about the viewing slits in the Mark IV's. I came to notice this while looking at the various pictures of the rear "door"above the petrol tank.

The APG tank, Grit and Lodestar have a thick steel plate with small drilled holes to look through.

Flirt has a periscope block in its place (if that's what you can call it, which seems to me the safer choice to look through, especially now I know that the enemy aimed at those viewing slits).

With Deborah, I could not make it out exactly - but the depth of the slit speaks for a periscope block.

Looking at the front compartment, all the survivors seem to have periscope blocks fitted.

The sponsons on APG, Grit and Lodestar are fitted with plates, Flirt and Deborah have blocks in their place.

I guess this could be a question for Gwyn, as maybe this depended on the manufacturer of the tanks? confuse

Or did they just probably use what came in, as both variants have the same bolt dimensions so that both can be used according to preference? Also, I guess that the drilled plate was cheaper to make...

With best regards

Martin



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Legend

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Definitely one for Gwyn, I think. I didn't understand at first what you meant by "thick steel plate...", but having looked at some pics I see the difference; although it might have been safer (only 'might') with vision blocks, I suspect vision would have been superior through the small holes in the steel plates - a sort of pinhole camera/camera obscura effect.

As far as I recall, you were thinking of painting the tank as 'Cxx (C22?) Cynic' - I don't suppose any period photos would show enough detail to tell which vision device is appropriate.

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PDA


Legend

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I'm fairly sure they started with periscopes but too many crew members were blinded, so they switched to drilled holes. So both are correct for modelmaking, but the drilled holes ones were later production.



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Legend

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Gwyn probably knows who built 2731, he may well know whether it was early or late in production. Hopefully he'll see this thread.

Regarding periscopes, the mirrors were not glass, AFAIK, but rather polished metal strips; safer, but I wouldn't be surprised if you couldn't see much from them - especially when the tank was moving.

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Legend

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It has always struck me as a bit strange that armoured glass vision blocks weren't used in early tanks. Capt. V.A. Mgebrov used armoured

glass blocks in the viewports of the commander's cupola on his 1915 armoured card designs.

Regards,

Charlie



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Legend

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Oh dear - such a build up in previous posts and I have to say I don't know all the answers you're looking for. I don't think that this is a point where a different manufacturer would have adopted a different design. There are actually very few differences between Mark IVs built by different manufacturers, and most of these seem to arise from the time they were built more than the manufacturer per se.

So, I'm not going to answer this tonight but will take a while to mull over other's comments and look at photos and then, maybe, hopefully, say something enlightening over the weekend.

As regards 2731 "Cynic", this was built by Metropolitan CWF. Between 13 July and 22 August 1917 it was C23, but by 15 November it had become C22.

Gwyn



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MRG


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Hello Gwyn,

thank you very much, that's very helpful already!

So, if Deborah was also by Metropolitan, then I could go for her configuration of vision slits.

As for the playing card sign, I am not so sure anymore as all tanks with the ace-of-spades (as far as pictures known to me go) came from 9 company - Cynic was 8.

The topic of insignia was discussed already in another old thread, so I will leave it at that.

With best regards,

Martin



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Speaking of glass viewers : Not so sure that "laminated" glass was already in current use during WW1.

The French manufacturer of laminated glass was TRIPLEX. They were using at first "Collodion" and later acetate sheets as an interlayer. British Triplex mfr was established later. Gemsco

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Legend

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Martin, from what Gwyn said, I would advise waiting, rather than copying the vision slits of Deborah - I understand him to say that time is more of a factor than manufacturer, so it's better to wait and see how close the two tanks were in construction, time-wise.

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Legend

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TinCanTadpole wrote:

Martin, from what Gwyn said, I would advise waiting, rather than copying the vision slits of Deborah - I understand him to say that time is more of a factor than manufacturer, so it's better to wait and see how close the two tanks were in construction, time-wise.


PDA wrote:

I'm fairly sure they started with periscopes but too many crew members were blinded, so they switched to drilled holes. So both are correct for modelmaking, but the drilled holes ones were later production.




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Legend

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What I meant was, "nobody has yet said whether 2731 Cynic was an early tank or a late one, so until that is established, it is best to wait". It may have a 2xxx serial number rather than 4xxx, but I don't know if that necessarily means it was an early build.

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MRG


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Hello all,

thank you for the feedback!

I guess that it will be wise waiting, but some time will pass before I get to the sponsons - and periscope blocks seem to have been fitted in the drivers tower all along. (3 in the front plate, 1 left, 1 right)

If there's one thing I cannot complain of, it's boredom - there's still loads to do in the mean time. Time is no problem.

As blocks and plates can be easily exchanged for another, maybe there even is no standard answer - as these could have been fitted according to the crew's preferences.

It is fun anyway, you trip over a detail and interesting things come up!

I never new that glass block periscopes as such were known in 1915, I would have guessed at that time they would all have been a simple two-mirror construction.

Best regards!



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Prisms were widely used in many military and civil applications from well before WW1, being generally more robust and with less deterioration in rugged use of the refractive components by comparison with reflective surfaces but more expensive and heavier. Binoculars, (some) theodolites, a considerable/bewildering variety of range-finders, field compasses and yes - periscopes - were some of the applications. The straight-through armoured/"ballistic" vision blocks are different and indeed stand on the shoulders of much (and continuing) research and development.

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Legend

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Deborah was 2620, also a Metropolitan build - earlier, but not that much earlier, than Cynic given the rate that Metropolitan worked. I'd expect them to be pretty similar if not identical. Complicating factor here is field repairs and modifications. Bits taken from scrapped tanks to repair others etc, but nevertheless...

Gwyn

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MRG


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Thank you very much for the information! I will go for Deborah's layout.

With best regards,

Martin



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Is this what's meant in the first post in this thread by the periscope block in the rear door? Does anyone have a photo of the interior of the rear door of any other preserved Mark IV to show whether this block is present, please?

Gwyn



-- Edited by Gwyn Evans on Sunday 24th of February 2013 09:31:22 PM

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Legend

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Actually I think this shows both types of visor:

Now I might be barking up the wrong tree here (or just barking) but is it the case that the periscope block is associated with a Lewis gun port (as in the rear doorphoto of Flirt II and the Male sponson internal photos I've just posted) and the thicker plate's where there'ssimply a vision slitthat isn't intended for use to aim a gun?

Gwyn
-- Edited by Gwyn Evans on Sunday 24th of February 2013 09:33:51 PM



-- Edited by Gwyn Evans on Sunday 24th of February 2013 09:41:00 PM

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Legend

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Still looking at this, and I note that in the side of the Female sponson there are both types, but that here I'd want to use the periscope in conjunction with the pistol port.

Gwyn



-- Edited by Gwyn Evans on Sunday 24th of February 2013 09:49:32 PM

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Legend

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There is a reference in the New Vanguard Osprey on the Mark I to the effect that the slits were covered on the inside by castings that held glass prisms but that these "invariably shattered under fire", as well as failing to provide very good visibility. If they were that bad then I can't imagine the same technology was used in the Mark IV when an alternative was available.

Gwyn

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Just found an internal photo of Lodestar III's rear door and yes, that has the thick plate instead of the periscope block. Very interesting - well spotted. This tank wasn't built by Metropolitan and is a very late production (one of the last Mark IVs ever built in fact). Nevertheless it does have some peculiar features and this is another one.

Gwyn

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MRG


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Hello Gwyn,

thank you very much!

looking at the rear doors on the APG tank and Grit, they seem to have the drilled plates and the opening under the lid is intended for a Lewis gun, guessing by the shape of it:

rearbracket.jpg

 

You can see the little holes of the drilled plates. Of course there was no gun put through there by default (the arrows are from my previous post and do not fit the subject here).

On Deborah, however, the depth of the opening speaks for a periscope block. It is hard to make out - but there is something behind that slit and the shadow is rather big for just a plate:

Deborah-Tail.jpg

The internal photo you attached with the periscope block on the rear door is of Flirt (I believe), and I have no idea who made that when.

The picture featuring the tail light (with the dog on the petrol tank) also hints at a periscope block.

Then there is the fact that periscope blocks seem the norm for the drivers' compartment in the front and I guess that area would have been prime target for the enemy to fire at. If the prisms were so vulnerable they would have been replaced by a different solution there first - and quality of vision would have been essential to them.

That's what makes me wonder under which reasoning either one or the other solution was placed and used - if there is a reasoning to it.

With best regards and thanks

Martin



-- Edited by MRG on Monday 25th of February 2013 06:16:02 PM



-- Edited by MRG on Monday 25th of February 2013 06:26:45 PM

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MRG


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I notice an interesting feature on the drilled plates, being the "L" shaped holes for the fixing bolts.

Obviously the plates could be shifted so that the holes were not exposed to the outside when not used. All pictures I have seen of plates show the holes aligned with the slit, so maybe the crew was thankful for even that little amount of ventilation this provided - or it did not matter as bullets did not get through those small holes anyway.

Another thing I noticed when I saw the plates on Lodestar III with my own eyes is how badly those little holes are drilled. They do not line up properly, the hole distances to another are rather irregular.

So they seem to have been done by hand without much of any stencil to go by. Also, some have 3 holes for each eye, others 4... But this is heading into nit-picking now. smile



-- Edited by MRG on Monday 25th of February 2013 06:50:19 PM

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Legend

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I've not been fortunate enough to see Deborah close-up, but I'm not convinced that the "depth" seen in the photo indicates a periscope block. Are you sure there's anything there? If the plate was missing then wouldn't it look just like it does? Nor is it obvious to me why you wouldn't be able to use a periscope block with the pinhole cover.

I noticed the three blocks at the driver's & commander's station. One relates to the gun, but the others seem essential, as you say, for the driver and commander to do their jobs so their use in preference to pinholes isn't surprising.

Yes, the cut-out in the rear door is indeed intended for a Lewis, should the need arise. (Another reason for not retro-fitting Mark IVs with Hotchkiss guns, perhaps?)

The sideways posted photo is of (the tank commonly referred to as) Flirt II at Lincoln. The Lincoln tank was built by Metropolitan but as we don't know its serial (the number painted on it is erroneous) when it was built isn't yet known. It is an earlier, rather than a later, machine though.

Yes, the L-shaped holes in the drilled plates are really ingenious.

Number of holes: Lodestar III has two pairs of three as does Flirt II, whereas APG and Grit have four, I think. This may be a manufacturer's variation, possibly.

You're raising interesting questions, and I need to look at this more...

Gwyn



-- Edited by Gwyn Evans on Monday 25th of February 2013 10:04:05 PM

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Legend

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Just found a shot of the inner face of the rear door to Bovington's Mark IV Male, and that has a periscope block.

Gwyn

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MRG


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I am quite sure that there is something behind the vision slit on Deborah's rear door, otherwise it would just be visible as a black hole.

The door is not thick enough to cast such a deep shadow on a drilled plate, therefore my reasoning.

The number of holes in the vision plates already varies on the ones fitted to Lodestar III, but I agree, the rear pleates on APG and Grit feature 4 + 4 cleanly drilled holes.

Another thing I notice is that all prisms on the surviving periscope blocks seem blind, there is no reflection to be seen whatsoever. Maybe the silver layer went black, as is the case with old mirrors.



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Legend

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I am in agreement with Martin that there is something behind the vision slit in that photo of Deborah's back door - and it does look as though it is set further back from the door plate than the vision plates were.

As for periscopes in the cab, I suggest that the plates would be unsuitable in this location because the eyes would probably have to be quite close to the holes in the plates to see properly - which is alright in a sponson, but no good when you're driving the tank and cannot use your hands to brace yourself rather than hit your head on the inside of the plating.

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Legend

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Yes, I agree regarding the positioning of the periscope blocks. They seem to be where someone needs proper vision to allow them to operate guns, driving gear etc. It would clearly be too much to ask someone to hold their face to the armour plate as well as drive, shoot or command. Probably the only ergonomic feature about the Mark IV.

On Deborah's back door I feel the jury's out. We can't see sufficiently well on the few photos we have, and we can't tell if this component is damaged or not.

Gwyn

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MRG


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Hi Gwyn,

I agree, it cannot be made out 100%. Anyway, I have decided for a periscope block - and if better pictures of Deborah turn up, I can still quickly change it for a plate.

As before, research makes results, here is what I did with the information:

MarkIVperiscope07.jpg

And - I could not resist - it "works". I just had to put mirrors in. wink

MarkIVperiscope05.jpg

MarkIVperiscope08.jpg

With best regards and thanks,

Martin



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Truly excellent. Congratulations.

Gwyn

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