I hope the chaps in that Sherman don't run into old blood 'n guts... he had something of a distaste for extemporised armour...
Tree trunks or cement might actually provide some protection against shaped charges and magnetic mines, which depend on proximity to the steel armour.
One problem - If not correctly worked out it was found that much extemporised armour could actually make shaped charge effects worse, as well as adding further stress to the suspension, slowing turret traverse etc..
Everyone has seen the photos of the many German Panzer Mark IV's equipped with add-on steel plate side and turret armor. The steel plates were relatively thin, mild steel plates maybe 1/2" thick if that. The intention of it was, of course, an attempt to detonate explosive anti-tank shells before they reached the main armor.
I'm sorry marc, it's a popularly held conception that they were for defence against rocket and shaped charge weapons, but it isn't true.
The Schurzen were introduced, and maintained, to deal with large calibre anti-tank rifles.
Given that they were first used in a theatre where shaped rocket weapons were virtually unknown, it's odd that the belief has carried on, perhaps fed by a US report of December '43 that assumed they were there to deflect hollow charge (the western allies having largely abandoned AT rifles by this point, they don't seem to have considered them seriously enough). Even some reputable authors have repeated the assumption, but have withdrawn from it as more German archive material has been inspected
PTRS/PTRD rifles could still do a great deal of damage right up until war's end, shattering wheels, sights, tracks and other components, particularly when deployed in packs of c.20 guns as the Soviets did. Every German technical reference to Shurzen seems to refer to it as solely about these AT rifle rounds. The effect against hollow charge as briefly considered later in the war was regarded as negligible, and sometimes, again, counter-beneficial as it could improve the stand off weapon's molten jet delivery in some circumstances.
It's also often said that the 'bedstead' wire mesh guards sometimes seen in imitation of the more common boiler plate schurzen was to aid against stand-off weapons - again, not true.
The Mesh was initially tested by Germany at exactly the same trials as the plate schurzen and found to be just as effective against AT rifle rounds, and lighter, the only reason it wasn't deployed at the time was manufacturing shortages of the right gauge of mesh.
Edited by Von Poop, 22 September 2009 - 09:53 PM.