Finally, if anyone feels really adventurous, how long before America's full intervention (post Pearl Harbor) were we training troops? Did we start militarization when Hitler invaded Poland or was it not till Churchill asked for assistance that we began really mobilizing?

Ostensibly, and due to the enormous strains of certain Senators and, of course, President FDR, the American military was preparing for war against a German enemy as early as 1933 or 1936. On the surface, the US were holding grand maneuvers in Lousiana and the Carolinas that would help develop a war-fighting doctrine, evaluate the newly formed Armored and Parachute units, and instill confidence into a rapidly expanding Armed Forces.

While there are definitely seeds of US success being sown during these 1940 maneuvers, such as the full integration between air reconnaissance and advancing ground forces, or the embryonic 'time-on-target' artillery tactic - we must largely consider these preparations farcical. The meteoric expansion of the US Armed Forces meant that quartermasters simply could not keep up; many troops were training with wooden AT guns and drilling with wooden rifles, practicing theory even when they should've been learning practical application. Further, there's even doubt on how connected the Top Brass were to the theoretical. Due to a disconnected, de-centralized system of branch expansion and training during the 20s and early 30s, the US Army simply had stupendous and often backwards understandings of modern equipment in action. At Carolina, a frustrated General Patton, commanding the 2nd Armored at the time, was shocked to hear that an enemy .50 cal emplacement had just destroyed the lead units of his armored columns! (Huston, Ed; The 2nd Armored Division: A History). There were undoubtedly visionaries, but quite a few 'evil geniuses' greatly hampered an intelligent expansion and modernization of the US Army prior to 1941 out of misguided branch loyalties. General Herr, the chief of Cavalry, was one such evil genius, and greatly hampered the mechanization of the US mounted forces; to a point where the 'Armored' and 'Cavalry' branches of services remained distinctly (and quite inefficiently) separate until the 1950s! Likewise, Infantry - considered the main combat arm in US "Open Warfare" doctrine was hampered by a WWI-esque tradition. The infantry remained convinced that they would be storming a series of static defenses rather than fighting a dynamic enemy; and put too great an importance on the accuracy of the rifleman and his co-ordination with the heaviest of artillery support. This, even at a time when the Germans were declaring the Machinegun the chief weapon of the infantry and developing a flexible, mobile squad-level machinegun, and using intelligent squad-level infiltration and night-fighting tactics. Where as, even by 1939, the US were relying on older 'massed platoon' movements that robbed NCOs of the ability to think for themselves.

Here's a few eye-opening snippets:

To deal with the impending crisis, maneuvers were held in Lousiana in the spring of 1940. One author wrote in the Cavalry Journal, "Our cavalry leaders, too, are seriously handicapped by too infrequent opportunities for combined training with infantry, divisions and higher echelons...."

The [maneuvers] was the first corps-versus-corps maneuver and the largest held in peacetime, involving seventy thousand soldiers. The maneuvers were designed to experiment with doctrine, leadership, organization and new equipment. Previously, when funds were available, each branch usually conducted its own training...independent of other combat arms. (My emphasis).

As we can see, it took until 1940 to fully kill this compartmentalization; this meant that the US arrived late to a party that their European counterparts had been experimenting in for almost 20 years; combined arms warfare. The discounting of armor by General McNair also severely hampered armor and crew training, consider...

General McNair was impressed with the deployment of tank destroyers during the maneuvers. He believed these new mobile self-propelled weapons would increase the pace of battle. More so, he still was convinced that combined arms meant the traditional infantry-artillery team."

Training was happening, on a massive, but slipshod scale - and the biggest obstacles to a large training regimen based in reality came from a number of sources;an outdated theoretical doctrine, lack of funds, lack of equipment - both exacerbated by isolationism - and the ghost of earlier branch rivalries from the early 1930s. The US was expanding at such a dizzying rate that training in all aspects was somewhat backwards, with perhaps the exception of Artillery and Airpower, in which the US had the luxury of drawing on some of America's greatest technical minds. Infantry was not glamorous, and often drew the 'dregs' who failed to make the USAAF or Armored forces, and were often subpar in quality.

The test of battle however, post-1942, began the US Army's doctrinal domination of true open, mobile warfare. Until the 'cold-water shock' of Kasserine Pass however, its safe to conclude that the US was woefully unprepared for war with a skilled foe.

Source: Through Mobility we Conquer... Hofmann, George F. 2006, Kentucky University Press