Somewhere I read that the planners thought we would need around 250 division. I think this was closer to 1939 or 1940. This was reduced as time passed and we ended up with around 100 divisions but NO reserves in the final stages of the war. We were not prepared for surprises at the end of the war. Thus another explanzation for the use of the atomic bomb.
George Marshall originally planned an army of 300 divisions, which we could have mobilized from the manpower available. However, there would have been corresponding cuts in manpower available for the air forces, navy and industry. Marshall did scale back to about 100 divisions (not counting the five Marine divisions). The main reason was for scaling back the army size was our commitment to coalition warfare. It was decided that we would provide material support to all our allies, and therefore manpower was diverted from the army build up to work in the industrial sector. Factories were not nearly so automated in the 1940s, and required huge amounts of labor. And when we think of Lend-Lease, we normally think of weapons shipped, but finished weapons were only a small part of the shipments.
Here’s a good website that illustrates the point in regards to lend-lease shipments to the USSR:
http://www.ordersofbattle.darkscape.net/site/sturmvogel/SovLendLease.html
The key line from this article is the idea that we were going to send all the support equipment so the USSR could concentrate on weapons production. Yes, the USSR produced massive quantities of tanks, guns and artillery pieces. On the other hand, they produced few trucks, little communications equipment, not much processed foods, etc....
All of that had to be produced somewhere, and it was produced in the USA with lots of American workers.
It was part of the strategic decision in coalition warfare that we would provide all the materials we could to our allies. The result created one of the great ironies of World War II. Stalin cut his deal with Hitler in 1939 because he thought that the allies wanted to “use” his army to fight Hitler w/o carrying their own weight (probably some truth to that). So in order to not let the Brits and French beat Hitler by spending copious amounts of Russian blood, Stalin signed the Non-Aggression Pact. He believed that the Hitler & the allies would exhaust each other and he would clean up. However, Hitler blitzkrieged the French, and then turned on the USSR. With the allies off the continent, they were in a position to offer Stalin much material aid and not take the heavy casualties. Instead, the allies defeated Hitler by spending copious amounts of Russian blood. Stalin wound up being forced to do exactly what he thought he had cleverly avoided.