Ram Mark II manual

[45jim]

You are creating a problem by converting from Imperial to Metric. If you are trying to determine the correct thickness of armour plate you need to remember the different methods of production and the inherent tolerance related to each. Only then can you convert. RHA (rolled homogeneous armour) has a much tighter tolerance than cast sections or face hardened plate. I believe you must select the correct source (original manuals) and then examine the relevant specification on manufacture. A common modern material MIL-A-46100 has a nice standard and is widely available and will demonstrate the methodology used in armour production and grading. It shows the variability in dimension and composition that was acceptable. Is this for wargaming?

[Matthew Noonan]

Originally Posted by 45jim

You are creating a problem by converting from Imperial to Metric. If you are trying to determine the correct thickness of armour plate you need to remember the different methods of production and the inherent tolerance related to each. Only then can you convert. RHA (rolled homogeneous armour) has a much tighter tolerance than cast sections or face hardened plate. I believe you must select the correct source (original manuals) and then examine the relevant specification on manufacture. A common modern material MIL-A-46100 has a nice standard and is widely available and will demonstrate the methodology used in armour production and grading. It shows the variability in dimension and composition that was acceptable. Is this for wargaming?

Tolerance thickness varied by date or nation, no idea what Canada was using. 0-5% is a good rule of thumb. With cast in the states I have seen spec sheets that will call for say 2 inches total thickness on a section, but then they will sate "equivalent to RHA plate" so they wanted cast armour that would act the same as if it was 2 inches of RHA, so slightly more then 2 inches in terms of cast armour total.

The spec sheet seems to be the most reliable unless someone in the future finds late manufacturers drawing plans, but was the tank constructed using an armour basis curve? it does not say, so again more confusion.

And if it is using a armour basis curve, what nations? the US? British? or did Canada have it's own? They evolved over time as well.

Example of a US curve from 1943.

http://i.imgur.com/IPU5D3F.jpg

Brig. Worthington had this to say in the summer of 1941 after talking to the British.

On cast armour

"In discussing plate thickness the opinion given was that working on a basic thickness for upright surfaces and then thinning down on the slopes was definitely bad practice. It was felt the sloping surfaces of a tank will be very often presented to normal impact and that therefore to depend on thin plates due to slope is asking for trouble. Whereas in the case of upright sides the resistance to normal impact is known at any angle beyond normal impact, the resisting power of the plate will simply be increased."

"I discussed the question of streamlining the top cast hull as on the Canadian M3 Cruiser. Opinions rendered indicate that so long as the basic thickness was maintained up to the gentler slopes, it could be thinned down with immunity where the surface is more horizontal. This point should be looked into"

[Marc van Aalderen]

Hello,

I can recommend this company for their fine reproduction manuals. Unfortunately no Ram manual at this time but you can email and ask if they have one?

http://www.afvhandbooks.com/index.html

Cheers,

[Matthew Noonan]

Thanks for the suggestion Marc.

I see the CWM (Canadian war museum) library does contain the earlier Ram I and II manual from 1942, but not the 1943 version for the II.

I think I saw that they have the parts list book as well.

They also have the full? report on the firing tests done on a Ram II turret front plate.

I have a short write up on it from the archives, but nothing detailed. so the full report, one would hope would list armour values for locations.

http://i.imgur.com/QRfuH1h.jpg
http://i.imgur.com/XiTXgjQ.jpg
http://i.imgur.com/y8T1vFZ.jpg
http://i.imgur.com/6PK6YUB.jpg

I'll see if they can make scanned copies and what they charge per page, If they get back to me I'll let everyone know.

(US national archives for example charge .80 cents a page for documents)

[Lauren Child]

Check before you pay for a copy.

The report may well gave useful info, but the service instruction books are large and don't usually cover the information you're after. You could pay a lot and not get what you're after. Same with the parts lists.

I've seen armour values on separate diagrams but I doubt these were provided into the field for obvious reasons, so they're not common.

Have you tried asking the archives folk at the tank museum in Bovington, UK?

[45jim]

Tolerance in cross section is not a function of location of manufacture but one of process control. Arbitrarily selection of a tolerance of 0-5% and calling it a "rule of thumb" isn't even rational as tolerance changes as surface area increases. Current thickness tolerances are about 2.5% for off the shelf rolled armour (up to 60" width) and most vehicle companies require tolerances closer to 1% (e.g. CMS 21). The standards exist for a reason, ballistic performance can be compromised by stacking tolerance in the wrong direction. Cast standards are also good, examine a cast iron engine block for example.

I wonder if you have misunderstood the notations on the cast US armour spec you elude to. Anyone who manufactures anything to a drawing makes it to the drawing (as close as possible within the confines of the process) so if it says 2" on the drawing then the final product will be 2". If there is a notation on the drawing that states "equivalent to 2" RHA" it most likely relates to the ballistic standard that that section must achieve as RHA is the standard by which all other metallic armours are compared.

The basis curve you attached has nothing to do with armour protection, it is a graphical representation of a simple mathematical calculation of cross section at various angles of attack. This is useful in calculating the reduction of weight achievable by using thinner sloped armour. You can tell this by the nice slope, penetration performance does not generate such a nice predictable curve. It quickly changes to ricochet at high angles of attack. If you were using this curve to predict armour performance you have a problem because as you approach 90 deg the thickness becomes the height of the armour sample.

Worthington knew what he was talking about regarding armour and that using NATO angles (normal angle to zero) is nice but it fails to take into account potential engagement angles in combat.

[Lauren Child]

Originally Posted by 45jim

Anyone who manufactures anything to a drawing makes it to the drawing (as close as possible within the confines of the process) so if it says 2" on the drawing then the final product will be 2".

Ah, that'll be MIL-TF-D41 compliance.

[Matthew Noonan]

Originally Posted by 45jim

Tolerance in cross section is not a function of location of manufacture but one of process control. Arbitrarily selection of a tolerance of 0-5% and calling it a "rule of thumb" isn't even rational as tolerance changes as surface area increases. Current thickness tolerances are about 2.5% for off the shelf rolled armour (up to 60" width) and most vehicle companies require tolerances closer to 1% (e.g. CMS 21). The standards exist for a reason, ballistic performance can be compromised by stacking tolerance in the wrong direction. Cast standards are also good, examine a cast iron engine block for example.

I wonder if you have misunderstood the notations on the cast US armour spec you elude to. Anyone who manufactures anything to a drawing makes it to the drawing (as close as possible within the confines of the process) so if it says 2" on the drawing then the final product will be 2". If there is a notation on the drawing that states "equivalent to 2" RHA" it most likely relates to the ballistic standard that that section must achieve as RHA is the standard by which all other metallic armours are compared.

The basis curve you attached has nothing to do with armour protection, it is a graphical representation of a simple mathematical calculation of cross section at various angles of attack. This is useful in calculating the reduction of weight achievable by using thinner sloped armour. You can tell this by the nice slope, penetration performance does not generate such a nice predictable curve. It quickly changes to ricochet at high angles of attack. If you were using this curve to predict armour performance you have a problem because as you approach 90 deg the thickness becomes the height of the armour sample.

Worthington knew what he was talking about regarding armour and that using NATO angles (normal angle to zero) is nice but it fails to take into account potential engagement angles in combat.

Many spec sheets from the period will list "Armour basis" you use the basis curve to find out actual, or in reverse if you know the angle of the plate and the actual thickness you could find out what it's basis would be.

The T14 assault tank for example, early spec sheets call for a (125-127 mm) frontal armour basis. The armour basis curve shows us how to find actual from that, which ends up being 50mm @ 60 deg. The actual front plate on the T14 in construction was 50mm at 60 deg. It's upper hull sides called for a 62.5 mm basis, which we know are sloped at 30 deg. Actual thickness was 50 mm. 50 mm @ 30 deg in the armour basis curve is 62.5 mm ( have seen 125 listed and 127 as basis, probably down to whoever was converting the value at the time either as 50 mm or 2 inches)

M6 heavy tank is another example of a vehicle who's exact specs are hard to find, but we do have the called for armour basis which was 127 mm frontal. So the vertical and near vertical surfaces would have to be physically at or near 127 mm, and the upper hull which was sloped at 30 deg would have to be around 101 mm to meet the called for spec.

There's a British AFV situation report update where they state the front of the Hull is 101.6 mm "Actual" as they don't list upper or lower front as location I assume it's for the majorty of the upper hull.

The Americans applied the basis curve to German vehicles as well at times. They knew the actual values, and they wanted to see the basis under their own curve.

http://i.imgur.com/9XPTyC6.jpg


The War Museum replied back to me, they are having trouble locating the files but are going to continue to look, prices are quite decent $6 for the first 20 pages, .30 cents per page after.

The National archives of Australia have some possibly interesting reports as well on the mounting of the 6 pdr in the Ram turret, along with drawings. Could be a possible source with dimension drawings at least for the mantlet and mabye the turret.