What would be the effects of earlier U.S. entry in WW II?

There has lately been some questions about the U.S. getting into WW II earlier but the only way that I can see that it if Hitler and Germany engage in Absolutely Stupid Behavior. As I see it if Germany act aggressively at the outbreak of war by sinking U.S. flagged ships in International Waters, demanding that the U.S. cease trade with any countries that are at war with Germany, THEN if the U.S. refuses, Germany declares war against the U.S. From my limited understanding of the state of the U.S. Military at the time, the first thing is the U.S. would do is mobilize reserves and NG forces. The U.S. industry would go on war footing. The first effect I could see is that the U.S. would be sending is Trucks, trucks, and more trucks to France as soon as they roll out the factory doors. I did not realize how much France depended on horse drawn carriages to transport supplies, so if we stick the with OTL timeline, France and the BEF should be fully motorized by March 1940. I have learned on this site that France over mobilized at the start of the war and it hurt the production of weapons, so with the U.S. in the war, France and Great Britain do not have to mobilize as fast. I believe that the B-17 just became operational and with deployment to France, it would force Germany to keep more of it's fighters in reserve for defense. So when would the first U.S. troops be arriving to France, and would that force Germany to act faster? What about Belgium and the Netherlands, would they be more inclined to Allies side if the U.S. was involved?
 

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The US won't declare war on Germany without Germany declaring war on the US prior to 1942 at the earliest. They didn't even declare war on Japan in 1937 despite the Panay Incident. Germany has her hand's full trying to fight the Allies until the Battle of Britain and has no reason to DoW the US and isn't stupid enough to do so prior to 1941. The US military isn't ready for war and knows it, so isn't going to support super aggressive action, FDR and Congress knows the public won't stand for a DoW without direct attacks on US soil (already there was a major spy ring broken in the US in 1941, US merchants ships were being sunk, and even a USN destroyer was attacked but the public wasn't interested in declaring war), while Germany has too much else to focus on to worry about the US until Pearl Harbor. Without radically changing Germany or the US it is tough to come up with a scenario IOTL that could get the US into the war early and it even got in as early as it did due to Japanese stupidity.

Hypothetically though assuming the US got in in 1940 or so they aren't remotely ready for war and will have to actually deny the Allies war materials they got IOTL to build up the US military earlier than IOTL. Even going to a full war time footing will take time, as IOTL by the time of Pearl Harbor a lot of work had already been done to prepare the US military for war that started in 1939; all that would have to be done before there could be significant expansion of US forces or ability to supply the Allies significantly. Much of the industrial expansion that turned into the flood of material happened in 1940-42 and was going to happen with or without war and needed to happen first, so IMHO probably not much changes overall in terms of how quickly the US military can get into the fight. If there is no Pacific theater and the US just gets into Europe, then they will be able to invade in 1943 and the war ends sooner, but the question is whether Japan sits still while that is happening given the embargo or the US DoWs them first. So the war in Europe probably ends sooner all things considered, but with greater US losses due to being ready to rush into France earlier if there is no Pacific theater.
 
Interesting idea.

I cannot comment on the potential on the grand scheme of things, but I could see an earlier involvment of the US looking something like this:

In the air US pilots, then US aircraft in very small numbers, and gradually increasing over time. One thing I have often wondered about, is what would have been possible with the US getting RAF instructors over on our side of the pond, looking over our training facilities/programs, and making improvements to better prepare our guys for the realities of war, before leaving the USA. It would hurt the RAF in the meantime, short term, by sending experienced pilots away from the fighting front, but if the hard won lesons during the BOB can be brought home to the USA war effort, then in the mid and long term, it would pay off with much better prepared pilots arriving, with aircraft already brought up to standards, and improved assembly lines churning out better/earlier aircraft than OTL.

On the ground, I would not look for anything of any real worth, mainly guys that would be able to see the lessons the French and British learned and being able to provide that information to out training and doctrine command (assuming we had TRADOC back then), so that the units that arrive are better prepared when they eventually get there.

At sea, we could see naval forces deployed within months of the Polish campaign breaking out, and with enough forces, perhaps the Norwegian campaign works, and Germany is kept out of Narvik. On the down side, does this mean the Japanese decide the time is ripe?
 
Interesting idea.

I cannot comment on the potential on the grand scheme of things, but I could see an earlier involvment of the US looking something like this:

... mainly guys that would be able to see the lessons the French and British learned and being able to provide that information to out training and doctrine command (assuming we had TRADOC back then), so that the units that arrive are better prepared when they eventually get there.

There was, tho each arms corps (later Branch) had its own staff for this. After the Jan 1942 reorganization into AGF, AAF, & ASF each of those monitored the systems for turning After Action Reports and similar reports into doctrine and training improvements. As with every like system in every army of every era the interpretation of the reports was uneven & influenced by the thinking of the individuals actually making the decisions on what improvements to make. Sometimes the 'improvements' were more of a step sideways than forward.

Still there would be some overall improvement. ie: the pair of Armor Corps engineers who were sent to Africa in early 1942 came back with the data that led to the specs for the T20 - T26 series tanks, and for at least a quarter of the 30,000 changes to the M4 tank design. If the US gets into the war a year or three years sooner then we get to tanks reflecting combat experience sooner.

At sea, we could see naval forces deployed within months of the Polish campaign breaking out, and with enough forces, perhaps the Norwegian campaign works, and Germany is kept out of Narvik.

Thats more dependant on the leaders at the top making the correct decisions. Still having another carrier, a larger surface fleet, and a combined arms Amphibious Force vs the relatively ad hoc landing force the French & Bris used sounds helpful.

On the down side, does this mean the Japanese decide the time is ripe?

Ripe for what? The Embargos were not yet conceived in 1940, Japan was still receiving loans from US banks, and little hindered in purchasing their needs in the US or elsewhere. Until the occupation of Indo China the warhawks in the US did not have political support to obtain any meaningful action vs Japan. Within Japan there was no clear concensus on moving against the Northern Resource Area or the Southern Resource Area, the short term policy was to focus on settling the China problem, & as long as the US & London banks continued to loan the Japanese government & industry the necessary capitol & material could be purchased there was zero incentive to start another war.
 
A early entry can make a big difference in US industry ouput. Although the US started mobilization in 1940 Congress did not pass the laws necessary to organize industry and resources. Nor was the War Dept (Army) funded to research the resources it needed. It was a open market & no manufactor knew if he could obtain the steel, electric wire, rubber, cotton, or at what price to fill a production contract for the Army. This hindered arms production and general preparation into 1942. Along with the assorted DoW voted on in December 1942 a series of laws were passed giving power to Federal agencies to take control of a wide variety of critical war materials and allocate according to necessary priorities. Along with that was funded a small corps of managers & clerical staff to determine just what resources existed and what the industrial capacity actually was. The various industry associations and existing government agencies actually had no useful data or information on how much of anything would be available & when.

Getting production properly organized in 1941 vs early 1943 makes for a big difference.
 
It takes major POD to start it, but if the US was a lot more paranoid on the build up of Nazi Germany and Japans expansion of hostilities in China, could they have things more in readiness by 1939? I know it is remote, but if the US had started the draft in 1937, added more building of weapons and research for new stuff, might they be able to contribute a lot more if war still begins in 1939?
 
The two key points in preparation of the Army would be: 1. Improving training for the officers and NCOs. Particularly the Reserve officers (60,000+ in 1939), and the National Guard (45,000+). As the 1920s conservative budgets & 1930s Depression shrank the War Dept budget cadre training was increasingly focused on the Regular Army.

2. Preparing a useful plan for industrial mobilization. Again a lack of funds prevented the War Dept from preparing a data base on materials & industrial capacity. Neither was there a worthwhile plan for equiping the Army ground and air corps beyond the existing Regular and National Guard formations. The exisiting thirty odd divisions of ground forces and supporting air corps peaked out at 1.2 million men if fully mobilized. War Plan Black estimated three times that would be needed. Congress never allocated funds for a staff of officers and clerical staff to prepare any useful planning.

The Navy was slightly better in this respect since simply keeping it afloat required robust planning, plus it was maintained at a level of combat readiness, vs the cadre status of the Regular & Reserve Army. Plans for WP Orange were relatively complete & the USN had a fair idea of what it would need to defeat the Japanese Navy and were that would come from.
 
Thanks. Theres a number of books concerning the US industrial mobilization. Currently have two on the shelf, 'A Call to Arms' and 'Freedoms Forge'. Both have some useful background on how the US transitioned from a token arms industry to the largest on the planet in 40 months.

John Ellis 'Brute Force' has several tables that illustrate how some of the production sectors increased twenty fold. ie: aircraft output went from under 5,000 machines in 1939 to 105,000 in 1944.
 
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