Ram Mark II manual

[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"