Ram Mark II manual

[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.

[Matthew Noonan]

Files came today, some lovely photos.

No actual thickness values are given for the turret front in the test other then the depth of the impressions left by the rounds that struck. Which is still useful as it can tell us some information.

Deepest indentation into the plate was 69.85 mm

The only area that they do give an outright value to is the horseshoe around the gun, which was 44.45 mm as a round struck that penetrated and then was stopped by the mantlet proper.


http://i.imgur.com/wTkNbVP.png

http://i.imgur.com/y9ST8zU.png

[Matthew Noonan]

Australian archives delivered the item I requested today.

Once you pay for something and they scan it, they add it to the website so anyone is free to view them in the future.

http://recordsearch.naa.gov.au/Searc...aspx?B=1664990

[Matthew Noonan]

Originally Posted by Matthew Noonan

Australian archives delivered the item I requested today.

Once you pay for something and they scan it, they add it to the website so anyone is free to view them in the future.

http://recordsearch.naa.gov.au/Searc...aspx?B=1664990

Paid to have the other files checked with the hope they had more, but it's basically the same as the other.

http://recordsearch.naa.gov.au/Searc...aspx?B=4938371

The CWM's copy of the 1942 manual has gone missing unfortunately. But the tank restorer had a copy of the 1943 one which they were able to copy.

Nothing on the Armour values in it as others had said. The general description included "The armour of the tank consists both of armour steel plate and cast armour steel. The lower hull is of armour steel plate riveted to suitable structural steel members. The top hull and turret are entirely of cast armour steel of varying thickness."

Except for one blurb in the turret section which seems to contradict any other source for thickness.

"The turret is a one-piece casting of two-inch armour"

Manual Lists the Gun as being able to elevate to +20 and depress to -7.5

In Canada's pride, Roger Lucy talks about the pilot Ram II tested in November 1941 on page 39 and 40 and some of the issues they had with it such as location of elevation gear, turret basket problems and such. He states they had concerns with the limited gun depression of the main gun being -10 to the front and -7.5 to sides and rear. Fixing it would have required redesign of both turret and rear deck. Joint committee on tank development agreed on December 11 1941 that -10 was acceptable.

Then on page 66 he lists the gun as being able to do +20 and -7.5.


I know the turret front plate changed at a later date and the inner mantlet had some tweaks at various times as well, but was the change so large that they lost 2.5 degrees of depression to the front from the pilot?

The Ram I with the 2 pdr is another ? on gun depression, I am guessing it was roughly in line with say what the valentine could do -15. Hunnicutt lists -10 but I believe this is incorrect. There are documents listing depression over the engine deck being limited to -12 or so after fitting intake protection plates for example.


The manual has some lovely diagrams and semi decent pictures of the tank.

I edited one and removed all the arrows crisscrossing it pointing out components to try and make a cleaner image for fun.

h6bFQCh.jpg
i.imgur.com/h6bFQCh.png

[Lynn Eades]

Mathew, as this is such an " in depth " discussion, have you considered the difference between the legally adopted British inch and the inch adopted by the USA.?
The 1922 comparison gave the British inch as being slightly less than 25.4mm and the U.S inch as being slightly more than 25.4mm.
Technically the U.S.is metricated in that its measurements are conversions of the metric SI system.


Apparently there has been between 5 and 8 different inches throughout the history of our planet.

And yes! I am just sh_ _ stirring.

The difference between the two above inches is 1 ten thousanth of an inch over 27 inches. (zip!)

[Matthew Noonan]

Originally Posted by Lynn Eades

Mathew, as this is such an " in depth " discussion, have you considered the difference between the legally adopted British inch and the inch adopted by the USA.?
The 1922 comparison gave the British inch as being slightly less than 25.4mm and the U.S inch as being slightly more than 25.4mm.
Technically the U.S.is metricated in that its measurements are conversions of the metric SI system.


Apparently there has been between 5 and 8 different inches throughout the history of our planet.

And yes! I am just sh_ _ stirring.

The difference between the two above inches is 1 ten thousanth of an inch over 27 inches. (zip!)

They do like to switch between imperial and metric at random it seems at times in archive material.

Weights are another annoying area. Is this imperial tons? US short tons? or metric. It's nice when they toss in a cwt in the figure so you know exactly what it is at times.