[LouisianaMan]

44,
Very good post! I was in a TDA assignment from '02 to retirement in '05, so learned something from your discussion of the M-1's troubles.

And yes, the decision to stick with the Shermans was a very close-run thing indeed. We had similar problems with the infantry, as our entire personnel management system was predicated upon an estimate that something like 85-88% of total casualties would be infantrymen, IIRC. When the actual percentage turned out to be something like 95%, we pretty quickly found that we were completely out of infantry replacements in the ETO by fall 1944, yet we had whole units of anti-aircraft artillery that stood idly by, unused. (At which point a lot of anti-aircraft guys suddenly became infantrymen, with or without any training!)

Regardless of how scientific an estimate may appear to be, it's no better than an educated guess that allows you to make some decisions and get rolling. Just like tactical plans, which are a commander's best shot at an immediate solution to an immediate problem, NOT a blueprint. Anyone who understands what a football team's "game plan" is will understand the concept almost perfectly.

IMO, both logistics and tactics are more art than science--definitely more than just crunching numbers, and definitely not foolproof. Despite the OVERLORD planners' detailed work and best efforts, everybody missed the fundamental importance of the doggoned hedgerows! (More recently, we apparently invaded a country and changed its regime without accurately assessing what would come next. Thus, a lightning thrust into Iraq became--surprise, surprise!--a protracted war and occupation.)