@ Calbear & CS:
It may've been
possible for the US to mobilize faster for WWII, but many folks still had the experiences of WWI misinforming them of how WWII would go- the US wouldn't have three years sitting on the sidelines before deciding to mobilize pretty much from scratch.
While the time to spin up from 1939-1942 was nearly identical but the US ramped up a lot quicker in raw production and knew it had to build up a capable military from 1940 on.
Did they make some bad decisions in what to build when and what to emphasize? See above. War is ruthless about showing whether your assumptions are correct or not.
1942 was brutal for the US Navy as it went up against both the KM and IJN with gusto and had to learn its lessons about what carrier a/c, Long Lance torpedoes and subs could do to ruin their day and how to counter them.
N. Africa was a godawful mess going up against good but weary, undersupplied troops in the Afrika Korps even with overwhelming air and artillery and logistical superiority.
We know now what gear and tactics worked best and adopting them a lot quicker would've been nice ceteris paribus.
The US Army had a major weakness that dogged it throughout WWII and afterward- a rather hostile indifference to properly equipping and training infantry (b/c they were disposable shock troops to filled by draftees, not capable professionals).
OTOH specialty units (Rangers) got everything they wanted in training and gear and were considerably to somewhat more effective than the usual grunts.
We have plenty of folks on the board wanking the German ideas about cultivating prowess in small-unit tactics and officer initiative that would've made the US Army's performance even more awesome.
IF the US Army treated their infantry as the basis for all other branches,
then a proper portable LMG wouldn't have been such an afterthought, nor would the bazooka been such a bust vs the Panzershreckt.
I guarantee you more M3 greaseguns (better, PPsh-44's, or better yet, reworked Stg-44's


) would've been available per platoon.
The US grunts fought hard, and if they survived, used a lot of tricks to make the enemy feel it, but paid a high toll in blood when they couldn't get artillery or CAS to take out enemy hardpoints.
As mentioned earlier, more US military observers learning from the Brits and Soviets what worked and what didn't against the Germans would've saved a bit of fumbling in N Africa and later.
Sure, having the stuff (gear, tactics, and strategy) we know now worked great in 1943 ready in 1941 would've helped.
However, there's a certain amount of fumbling around ANY organization does until it gets the institutional memory and general competence to deal with present threats.
If it has any savvy about what technical, economic, and political trends are in motion, it can deal with anticipated threats.
If it has a decent grounding in history, the repertoire of tactical and strategic possibilities they can develop is remarkable.
Sometimes, as the French found out in 1940, no matter how good a learning curve you have, elan and creativity don't mean shit if you can't move and hit the enemy hard enough in the right places for the situation to change.