Landships II

CharlieC · Legend

Missing tank articles on Landships II

CharlieC · Legend

�

Here is my proposed text for the Medium D article.�

Regards,

Charlie

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TinCanTadpole · Legend

I'll have a look at your text in a moment Charlie, but first I can say that I've read, exactly where I'd need to have a look, that there are very few photos of the D* and all were taken after it was put out to pasture, so it's unlikely you'll find any more than the well-known one often erroneously identified as the D**.

TinCanTadpole · Legend

Okay, generally the text looks good, but I have a few suggestions:

1) change original width from 2.2m to 2.26m

2) more detail about design changes; the D* was not just widened, it also had the turret (citadel) moved forward and longer-pitch tracks. I don't have exact figures for this, but the calculations I did for my unfinished Medium D drawings suggest the original D, D** and DM used a 7.5" pitch, whereas the D* uniquely had a different length of link - somewhere around 10", but I haven't worked out a more precise figure.

3) D** was not just widened from 2.56 to 2.7m, it was also lengthened from 30' (9.144m) to 31'10" (9.7m). I've not seen a photo of the rear of the D*, but either that model or the D** introduced a new flush-plated rear instead of the track-horned rear of the D.

4) the text suggests the D couldn't have crossed a verticle obstacle going forwards (or virtually so), but this is misleading: design specs called for the tank to be able to climb a four-foot obstacle in one direction and a six-footer the other way. The noticeable rake of the track makes it look as though the front is very low, but in fact the top of the track is around five feet above ground at the idler, around seven feet at the sprocket. Assuming the D could indeed meet the four-foot requirement going forwards, it would have had a superior vertical obstacle performance than the majority of modern MBTs, few of which can manage three feet or more, and the top of the track at the idler, at or approaching five feet in height, is little lower than the 5'1" axle height of one of the more rhomboid-like designs (need to check whether it is indeed for rhomboids, or for Medium C).

5) the reason for the lower front ought to be explained - that the modified Whippet, with it's high engine deck, suffered poor visibility, so the design for the D was effectively a reversed version of it, so that the crew could see better. Knowing that, and that the D was designed to cross a four-foot obstacle going forwards, I consider it unfair to look on the lower front as weird.

6) Re the Indian trials, I suggest that more be said. Mention of the asbestos covering given to at least one of the tanks (the Fowler-built one. The other tank sent to India appears to have been one of the Vickers/Wolseley examples). Also that the two tanks were supposed to be demonstrated at Ahmednagar, but both broke down en route from the railway station there to the local army camp, the crippled tanks being towed in and apparently never moving again.

7) whilst I'm obviously interested in the D and want to see it written of as favourably as possible, I would add in that it had a major design flaw in that it would be immobilised by the failure of the wire ropes on one side.

8) more about the decisions behind the production, numbers, and the demise of the design - stating the uncertainty if necessary. My understanding is that it was Churchill who pushed for the design, in competition with others who backed production of the more conventional Medium C (this according to The Devil's Chariots), and that pushing ahead with prototypes of the D came at the expense of Medium C production being halted.
Originally 75 tanks were to have been built, revised down to 20 because of costs, finally reduced to three. There is some uncertainty over whether two or three DMs were built, but if memory serves photographic evidence might support three, based on detail differences. Would need to check that though.
Numbers: Medium D 13.5 tons, 240hp Siddely puma; four built by Fowler, with number two using some recovered components from the fire-damaged first tank. Fowler number four was apparently not completed. Two D s, I think, built by Vickers/Wolseley - you can tell them apart because the Fowler tanks seem to have had a turret roof that curved from side to side, whereas the Wolseleys had a two-piece roof with flat plates joined by a chine. Medium D* 14.5 tons, possible change from three-speed epicyclics for steering to four-speed, possible adoption of hydraulic controls, same engine as D but speed on flat increased to 24mph (must be the change in gears); one built by Wolseley.�Medium D** 15 tons, may have used different engines at different stages of trials; definitely an R-R Eagle 370hp, possibly also a 300hp uprated Puma. Apparently tested with hydraulic drive, which increased weight, and managed 31mph at one point, but which engine/transmission gave this performance is unknown; originally built with four-speed primary gearbox and clutch/brake steering instead of the fwds/rev primary 'box and epicyclics of the D and D*; one built by Wolseley.�Medium DM weight up to 18 tons, performance down to 20mph; two, perhaps, built by ROF Woolwich, which I think the text already states.

9) Possible smear campaign used to exaggerate problems (according to Military Modelling), presumably in order to give an excuse to abandon an expensive project at a time of postwar financial stringency.

10) more about related designs - even if only brief sentences. Johnson's Light Infantry Tank needs to be mentioned, being an improved version of the concept in a more compact package. Different track design using the same principles (and a length of track surviving, plus two bogies), refined version of wire-rope suspension, using cams to tension the ropes and control movement - to reduce/prevent slack which caused the Medium Ds to sag at one end. Around 21 feet long, 7.5 tons, 100hp, probably same 2.26m width as original D.

Johnson's�Tropical Tank series, built shortly after the Light Infantry, dispensed with the snake track but used wire-rope suspension.

French�Char de Bataille competitors in mid-20s, both the Schneider-Renault SRA and the Saint Chamond FAMH used original-style Medium D snake tracks without wire-rope suspension. Another one, the FCM 21, didn't have proper snake tracks, but appears to have had non-functional lookalikes.

11) just to make sure people realise that this design deserves fair mention in tank history, I would point out that it was the first fast tank to be designed as such, and that it was designed for, in effect, Blitzkrieg - long before the Germans put that theory into practice.

That's a lot, I know, but as it stands I think the article concentrates a bit much on background and lacks detail about a tank that is too-much neglected and deserves to be written about.

CharlieC · Legend

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Thank you very much TCT - just what I wanted.

It's quite hard to find information on the Medium D - most authors just wave the tank away as an oddity which was flawed rather than examining its strengths.

I think the Ordnance Dept evaluation of the track/suspension system was more even handed I guess because the M1922 hull was much the same as the more

conventional M1921. At least the M1922 had the driver in the centre at the front which seems to have been a point that authors focus on when criticising the�

Medium D.

I'm not sure I want to get into detail about the derivative Johnson designs - perhaps these should be in a separate article - but a quick mention sounds like a good

idea.

I'll revise the article with your suggestions thanks again,

Regards,

Charlie

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CharlieC · Legend

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I didn't know about the Schneider/Renault and FAMH prototypes. The SRA prototype looks as though it has a ball jointed snake track

rather than the cable track used on the Medium D.

I think a separate article on these tanks, with a link from the Medium D article, is the best way to handle them since the French prototypes are important because they are

in the line of development which lead to the WW2 Char B1.

Regards,

Charlie�

�

TinCanTadpole · Legend

Glad you're pleased with that, Charlie, I wondered if it was a bit much.

Re SRA tracks, if it had ball-jointed links it would need to have had a hybrid track, using the original cast shoes and wooden sabots of the Medium D mounted on the ball-jointed cable of the Light Infantry track. I'm not totally sure that the SRA used cable links identical to those of the D, but having recently seen a bigger version of the side view featured on the Chars-Francais site, I can say that the cast shoes pivoted on the links in the same manner as those on the D - ie, the cable did not twist, the shoes rocked on hinges.

As far as I see, this is not so on the ball-jointed track of the Light Infantry tank, which appears to have had the cast/pressed metal track shoes fixed firmly to the tubular links - relying on the ball joints to allow individual links to twist. According to Army and Navy Modelworld magazine, the Light Infantry tank's tracks had problems with their lubricating oil, which sloshed around inside the links; Thinner oils leaked out and thicker ones collected dirt, so perhaps it was not as practical as the original design - the French would have had a few years to learn how British trials went before the completion of their own designs, so they may have chosen the safer route.

The Medium D track was confusing to me for quite a while, and I still don't know the exact shape of the links that form the chain, but I'm fairly confident that the track is not a cable as such. I've read of it described as a cable or as rope tracks, which tends to suggest a continuous metal rope rather than a chain of separate links, but a chain of links is what the D had. Each link seems to have a half-tubular back, forming the rail along which the road wheels run; at each end are chunky loops for track pins - twinned loops at one end and a single one at the other: these loops are not flush with the top of the link, so the back of the track chain appears knobbly at each joint; in the middle of each link is the pivot for the track shoe, which is a u-shaped section running sideways across the link; the track shoe has a tongue running side-to-side, which slots into the channel of the U-section - I assume there is a longitudinal pivot pin joining the two; apart from that there are some webs reinforcing the U-section, which overhangs the link at each side - I now believe the sprocket has two sets of teeth, straddling the link and engaging with the ends of the U-channel and, possibly, with the ends of the track pins, which on the D also overhang the link at each side. I'm not sure the track pins do this on the SRA, it looks to have smoother tracks than the bumpy form of the D's, but otherwise I think them similar.

One more thing - for the M1922 rather than the Medium D - I think there may have been more than one example built. No idea where, but I think I read somewhere online that there were as many as six prototypes; even if that's wrong, there is certainly reason to think there were at least two, as the surviving (or, hopefully still surviving) example has T-section angle irons rivetted down each side amidships, but there are photos online of an M1922 that lacks these.

CharlieC · Legend

�

Hunnicutt in his book on the US medium tanks says only one M1922 was produced. There is also a manual of US tanks produced about 1940 that says only one M1921 and M1922.

The financial constraints placed on the US Army and the internal political fighting between different branches of the army meant that the only new tanks authorised were experimental

vehicles for most of the 1920s and early 1930s. �Only a very few promising types were produced in tiny numbers for troop trials.�

The M1922 was used as a test bed for various tank components after the initial trials so additional pieces may be related to the trials rather than representing a different

vehicle. I've got requests out to a couple of contacts in the US to try to find out where the M1922 is located now.

Regards,

Charlie

TinCanTadpole · Legend

Just checked the sectional drawings on Wikipedia to see what the idler axle heights are, in regards to what I wrote earlier about climbing performance:

1) Mk VII, therefore also Mks IV, V - 5'1" (1.55m)

2) Medium C - 4'4" (1.32m)

3) Medium B - 3'8.5" (1.13m)

For comparison I can give only a vague figure for the Medium D, as the sagging effect I mentioned often means that in the few photos around you can see some squat at the back and consequent rise at the front - which makes calculations difficult. Nonetheless, the figure in memory is around (maybe just below) the one metre mark - probably about 0.97m when level, rising to about 1.06m when the tank squats. This is lower than the B, the C and the heavy tanks, but probably better than the Whippet - which didn't have the option of climbing tall obstacles in reverse!

CharlieC · Legend

�

I've finished the first version of the Medium D article so I'll put it on Landships II today. If nothing else the article may provide a small

amusement.

A point on the Medium DM - I don't think it had return rollers - on one of the images it seems as if the track slides through a guide rather�

than rolling over a wheel. Certainly the US M1922 had return rollers.

Regards,

Charlie

�

-- Edited by CharlieC on Friday 8th of November 2013 05:18:42 AM

TinCanTadpole · Legend

I did some work on my Medium D drawings tonight for the first time in ages; overlaid a side drawing of a Whippet out of interest, and found that the rise of the lower track run going forwards is more or less identical for the two tanks, really only differing once the track curves around the idler as the Medium D has a larger diameter radius of curve and consequently higher axle height.

More relevant to this thread, I've decided to try to draw a four-view of the Medium D(M) rather than the original Medium D: I cannot currently complete drawings on the early tank because of uncertainty about the shape of the transmission casing between the rear track horns, but the D(M) should be easier to work on, even if it will still be a case of doing an approximate drawing rather than a really exacting one. Nonetheless, if I can complete such a drawing (some weeks in the future, I expect, not immediately), I hope it would be a useful addition to the article.

CharlieC · Legend

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I think you'll have to accept that we speak different dialects of English and it leaks through into writing. I do try not to use Australian modes of expression (e.g. no irony) when I'm

writing for Landships II but inevitably some will leak through.

I'll fix the factual problems with the text - no worries.

I'm not sure I want to go any further with the tropical tank, I think a fuller discussion of this vehicle should be in its own article.

�

I did wonder about the use of aero-engines in the Medium D. There is a long article in Russian on tank transmissions on the web (can't remember where I saw it).

This article was very critical of the use of aero-engines in tanks. The argument, as I remember it, said that there's a mismatch between the rev/torque requirements

of an aircraft compared to a tank. Back it the 1920s and 30s it would be a rare aero-engine which could rev past 1800-2000 rpm, to match this to a tank would require a massive

transmission to handle the torque delivered at low rpm. An ideal tank engine would deliver max. torque between 2000-3000 rpm which resulted in a much smaller

transmission with lighter loads. There may have been some self-congratulation going on here since the Russian V2 diesel fits this spec exactly.

Another issue with aero-engines is that they aren't designed to be throttled up and down dependent on ground conditions.

�

Do you have a scan of the article in�Army and Navy Modelworld? I won't include a reference unless I've read it and it adds to the general argument.

�

I'll take the demise of the Medium D away and think about it - I agree the idea could be expanded.

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Sorry - the book didn't have the dimensions of the M1922 - I guess you could approximate it from the turret diameter since the turrets were the same between the M1921 and M1922.

My eyeball says the M1922 was longer than the M1921.

Regards,

Charlie

-- Edited by CharlieC on Saturday 9th of November 2013 05:56:33 AM

-- Edited by CharlieC on Saturday 9th of November 2013 05:57:38 AM

TinCanTadpole · Legend

You've done a good job on the article, Charlie. There are one or two minor things I would have put differently myself, but the balance is much better than the original draft and the machine receives a fairer press.

I can point out a couple of errors though:

1) the D** introduced the cam-operated clutch/brake steering, not the D*, which retained (epicyclic) geared steering - but with an extra speed compared with the D.

2) the first photo under the D** section needs to be moved up the page, because it is actually the D*. This particular picture is often identified wrongly, as the forward position of the turret/citadel, the chine roof and absence of a cupola all make it look like the wider, longer vehicle - which was built by the same manufacturer. If you look at the track return guides you'll see the supports are different, which is the quick way to tell the two apart; further confirmation can be found for anyone who can be bothered to count track links (!), as the number along the flat section of the track return (roughly speaking from the top of the idler to the top of the sprocket) is only about 37 links on the D*, whereas the D has about 43 in the same length because of the shorter track pitch, and the D** has about 46 because of the extra length.

Regarding Tropical tanks, there were four in total, one of which was, as you wrote, turreted; I think some of these machines were sent to India for tropical trials in 1923, but proved troublesome because the water-cooled engine had been marginal on cooling in Britain! Although they were abandoned as an idea, they did form the basis of the Dragon Mk 1 arty tractor, which ditched the wire rope suspension for conventional means.

On Medium D reliability, I get the impression from Army and Navy Modelworld mag (which may be worth adding to the sources list) that this may have been because of the amount of power available - I think the transmissions couldn't really cope with it, a problem which might have been averted if they had stuck to the trusty old Ricardo. Perhaps they thought it too slow-revving.

Would you consider writing a little more about the demise of the project? It's the one area of the article that could do with a bit more - not a lot, just enough to mention that postwar stringency meant that any vehicle would be scrutinised extra-well when decisions were made whether to adopt or not, and that the problems of the D may have been exaggerated in order to cancel the project and save further expenditure. Churchill moved to a different department around 1921, so after that he was no longer around to back the project.

On a different note, thanks for the pointer about the return rollers, I'll have a close look to see if it had any.

Also, does your source on the M1922 give any dimensions? Based on the dimensions for the M1921 on the old "Tanks!" website, and on my own estimations using the assumption that the pitch is likely the same as the Medium D at 7.5", I guess the length to be about 24 feet, plus/minus six inches. Can you confirm?

CharlieC · Legend

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I've just pushed an article on the Medium Mark C onto Landships II.�

The Medium Mark D article has been updated.

Regards,

Charlie

CharlieC · Legend

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I've been researching the French "Char de Bataille" project. Three of the four prototype tanks produced in 1924, the Schneider-Renault SRA, FAMH and FCM 21 had snake tracks.

None of them used Johnson's sprung cable suspension. The SRA had leaf spring suspension, the Schneider SRB had a hydraulic suspension (no idea how that worked),

the FAMH (Saint-Chamond) had a hydropneumatic suspension and the FCM 21 used a variant of small wheel sprung bogies used on the FCM 2C.

Regards,

Charlie

�

-- Edited by CharlieC on Sunday 10th of November 2013 09:14:00 AM

TinCanTadpole · Legend

Interesting about the Char de Bataille - as far as I knew, the FCM 21 was unsprung, but I think that did come from the Wikipedia article on the Char B, so it depends how good the source material was. As for it having snake tracks, I'm not sure; it has something looking like a snake track, but the links below look wider and chunkier and the shoes don't look as though they'll pivot.

I agree that M1922 looks longer than M1921; thanks for looking and suggesting the turret comparison.

On the use of aero engines in tanks, I take your point about the variation of running speeds: the Siddeley Puma used in the earlier Medium Ds is said to have been known for unreliabilty - presumably in aircraft. I imagine it would have been chosen because in 1918 and the next few years, 2000rpm would be high revving for a tank - we have to remember not to look at it with hindsight and the knowledge that later tank engines would rev higher, but instead consider that contemporary tank engines revved around 1500rpm, and the rhomboids had been even slower: 1000rpm for Mk I and 1200rpm for Mk IV. By such standards, the 2000rpm an aero engine could provide at the time WAS high-revving and would likely seem more flexible than the 1600rpm or so the Ricardo could offer. I suppose that, although not designed to be revved up and down regularly, aero engines are designed to be started up and quickly run at high revs.

CharlieC · Legend

�

The FCM 21 is referred to as a scaled down FCM 2C - the suspension on the 2C was lots of small wheels and leaf springs. The 2C suspension system was regarded as

ineffective and no better than a rigid system. I found a large version of one of the FCM 21 images (detail attached) - the track looks like a variant of Johnson's ideas but the track plates

certainly couldn't have swung around.

The Puma engine fitted to the Medium D was a total dog - it was only fitted in numbers to one aircraft - the D.H 9 and the engine was found to give poorer performance than the engine

in an earlier version of the D.H 9. It was replaced by a Liberty engine - another engine which had major problems - but the Liberty engine improved the performance of the D.H 9.

It seems as if there was a view in the British hierarchy that - "We've produced all these aero engines that aren't fit to be put into an aircraft, here's an idea, let's put them in tanks".

They were still doing this into WW2.

I had a reply that the M1922 may be at Fort Lee, Virginia with the rest of the Aberdeen collection. The informant thinks he'll be at Fort Lee in early Dec and will have a look for it.

Regards,

Charlie

TinCanTadpole · Legend

If your chap does get the chance to see the M1922, do you think you could ask if he would take a few close-up photos of the track links, from various angles? I think the design is either identical to or at least very similar to that of the Medium D, and whilst I now have a better idea what shape the links were, it would be useful to see the underside of the joint between links, and the joint between link and track shoe.

Re aero engines, well - I suppose a tank won't fall out of the sky if the engine stops...

MK1 Nut · Hero

Hiya,

I've been having a poke around and came up with the patent for the Clark Track I think it's the American version.� confuse

On the same page it mentions it is an improvement on the Johnson system. They give numbers but I haven't found anything.�

�Patents 1,329,769 granted Feb. 3, 1920 and 1,330,119 granted Feb. 10, 1920 of Philip Henry Johnson.

Hope that helps

Helen x

Clark suspension

Johnson Suspension

-- Edited by MK1 Nut on Friday 15th of November 2013 10:12:08 PM

-- Edited by MK1 Nut on Friday 15th of November 2013 10:17:09 PM

CharlieC · Legend

�

I had a reply from the Ordnance Museum people - the M1922 is located in the�Army Storage Depot in Anniston, Alabama.

I think it's unlikely that it will be restored in the forseeable future. Anyone have contacts at Bovington? - I would think they would be interested

since the M1922 has the Johnson track and cable suspension. The US Army doesn't seem much interested in it.

Regards,

Charlie

CharlieC · Legend

�

Helen,

It certainly does.�

I'll have to do some deep study on the patents but I think the patents relate to the track/suspension on the Medium Mark D and the Light Infantry Tank.

As far as I can tell the track/suspension used on the US M1922 medium tank was much the same as the Medium D track. Hunnicutt says the Ordnance Dept

used British drawings to build the suspension. The rather poor image in "Sherman - US Medium Tanks" seems to show a suspension system like Johnson's

patent rather than the more elaborate Clark system.

Thank you,

Regards,

Charlie

-- Edited by CharlieC on Saturday 16th of November 2013 02:25:08 AM

CharlieC · Legend

�

I was curious about the assigned company on the Johnson/Clark patents - Roadless Traction Ltd.

The company was set up in 1919 by a group of army officers lead by Colonel Philip Johnson with Captain Edward Firth, Captain G. John Rackham, Captain Oscar Styles Penn,

Lts. Shaw and Frederick Lamb. They were all involved in designing tracked systems for the army during the war.

After the Medium Mark D Roadless Traction designed and built 4-wheel drive systems and track conversions for tractors. It seems to have been modestly successful and remained

in business until 1983.

There is another aspect of Johnson's relations with the Army and bureaucrats that I hadn't considered - class prejudice. I found a potted biography up until WW1:

"Johnson was born in 1877, and educated at King Edward VI School Birmingham, before studying engineering at the 'Durham College of�

Science' in Newcastle. He then served an apprenticeship in various ship building and engineering firms. He tried to enlist in�

the Army in 1899 for the Boar war but was rejected for poor eye sight. So he travelled to South Africa and managed to get seconded�

to the 48th Steam transport Corp. of the Royal Engineers for his steam experience. Here he met up with a Lieutenant-Colonel�

Crompton who also had an interest in engineering. The Corp had Forty-Six traction engines (41 being Fowlers). When the War ended�

he was taken on by Fowlers and returned home to Leeds. For Fowlers he worked in R & D and travelled to India as sale representative.�

In 1915 he returned home and was attached to the Ministry of Munitions where he then got involved in tank design and was�

commissioned as second lieutenant in the Army Service Corps."

�

Apparently Johnson wrote a report towards the end of WW1 in which he asserted that the limitations of tanks used in WW1 were due to

deficiencies in design rather than their operational use. I can see that really endearing him to the hierarchies associated with tank

design and production.

Regards,

Charlie

�

-- Edited by CharlieC on Saturday 16th of November 2013 01:54:56 PM

TinCanTadpole · Legend

I had another look at M1922 and Medium DM tracks a couple of days ago, and I came to think my last post was incorrect in suggesting the two had more-or-less identical tracks. There appears to be some form of rail sticking out of the sides of the American track link, to run along the outer rim of the idler and the road wheels in the bogies. The main central rail of the link sticks up between these side rails, into the pulley-groove of the idler or road wheel. This does not seem to be present on the British track, nor the French SRA track, which I now think is closer to the British track than is the American.

The pressings for the M1922 track shoes differ slightly at least, having lips protruding on leading and trailing edges, and I suspect the pivoting mechanisms to be different as well.

Would be good if Bovington could acquire the M1922 and restore it, as it is an interesting vehicle that deserves better than to languish and rust. There are more than enough Shermans in the world, but only one M1922.

CharlieC · Legend

�

I've had confirmation the M1922 is in storage at Anniston Depot. It is possible to get permission for access to the M1922 for research purposes - I've been sent a couple of contacts

- so, if anyone is in Alabama......

I agree the M1922 track seems to be somewhat different to Medium D track - I'm not convinced the M1922 had swivelling track shoes like the Medium D. The French implementation

of the Johnson track seems to have had fixed track shoes.

So - who do we write to at Bovington to try to raise interest in acquiring the M1922?

Regards,

Charlie

MK1 Nut · Hero

Found this �M1922�definitely wobbly track. :) Hx

CharlieC · Legend

�

Absolutely so - I haven't seen those images before, they were taken in 1983, I wonder if they neatened the tank track before the 2008 image was taken.

You can just about make out the swivels under the track shoes.

Regards,

Charlie

TinCanTadpole · Legend

I don't think the French use of the snake track was a dummy (except on the FCM, where the shoes were clearly fixed to the links), there is slight undulation visible in photos if you look closely - I think the SRA and FAMH had functional snake tracks, but were either photographed after driving on a flat enough surface not to have disturbed the shoes, or were neatened up before saying "cheese".