Appleknocker wrote - Pre-war strength combat losses represent a qualitative decline in personnel and difficult to replace equipment, which has a direct effect on combat effectiveness
i think it is pertinent to say that from 1939-June 1941 - The losses incurred by the Heer numerically and qualitatively did not incur a decline in personnel or performance. (although the Luftwaffe suffered in this way following the Battle of Britain)
Once you reach 1941 and beyond then i think Appleknocker is quite correct... But declining quality of personnel and training is due to more than just the pre-war strength of any army being equalled then overtaken by the losses it incurs. But simply put you use the best first and a large number die quickly... the longer a conflict goes the more causalties you incur and it becomes inevitable that quality suffers.(depending on how many losses you incur, and the size of your manpool)
If your army and its operations are based on the quality of combat soldiers (the combat arm being a small percentage) it will always have an effect.
i firmly believe that for Germany
heavy casualites combined with the loss of its better trained soldiers over time led to a shortening of training and simplification of its methods, leading to its combat arm becoming less effective
Ljadw wrote -(!)The US lost almost their total pre war manpower during the war, but this did not prevent the US to win the war . It was the same for Britain .
(2)German infantry losses from Barbarossa are not the same as the loss of the German prewar strength .Germany lost 800000 men in Barbarossa which was the equivalent of their pre war strength, but only a small number of them belonged to the prewar WM .
(!) The US losing its pre-war manpower is totally different in its effect than from when it happened to Germany. (this is where overall losses become important)
(2) Some of the losses in Barbarossa would have been from the pre-war Heer........ who had fought through 1939-1941
None of it is irrelevent ... That the Soviet union could lose its whole pre-war strength but mount sucessfull operations in late 1942 only points to the available pool of manpower introduced after 1941....
And the structure of soviet training and its profligate use of its manpower...
If you base your methodology around simple training for all then you can survive with your combat arm having less quality.
And there are so many other factors which mediate these ideas that it is very hard to draw sufficient comparisons between different armies.