The issue with this kind of take on the situation is that while America has a lot of potential, they are not actually 1945 America yet. When America entered WW2, they didn't have functioning torpedoes. The Mk.14 literally clonked on ships and failed to detonate.
That was an issue deriving from budget cuts in the Great Depression, I believe. The problem was that they couldn't afford large-scale realistic practice, and the technical glitch didn't reveal itself under conventional testing.
Was America an industrial power to be feared? Yes, absolutely. Does America have the capability, in 1915, to beat the Royal Navy with the US Navy? No. In 1915, the Royal Navy outnumbered them by 2-1 in Dreadnoughts, and more than that in modern cruisers.
It bears keeping in mind that a good part of this navy is spread across the world protecting the largest empire in history, and most of the rest of it is currently patrolling the English Channel seeing as the Krauts just became their worst nightmare: a mainland European hegemon.
Against Britain alone, maybe it would be possible to be enough of a menace that the Royal Navy couldn't effectively concentrate their forces to raid and destroy US naval bases and dock yards, which would eventually lead to a US capable of slowly, after a long and costly war, force Britain to sue for peace.
That attitude largely depends upon who declared war and why. Seeing as both nations are democracies, whoever'd win would largely correlate with whoever's capable of keeping their citizens' war support up.
When Britain has the assistance of Japan, whose navy is approximately 80% (I think) of America's in dreadnoughts, they can now force concentrate on either coast and just flat out win any naval engagement, meaning that they get free reign on shore bombarding dockyards, which aren't exactly rebuilt in an afternoon. And here's the thing: you can't get a dreadnought down a river, so you can't build the ships inland. You also can't get it on a train. Sure, Japan might need 6 months to a year or so to get to the U.S. west coast, but there's a limit to how fast you can build and commission ships that displace tens of thousands of tons.
The critical answer here is force concentration, I believe. Japan would probably concentrate on taking the Philippines, and if they're
super successful, trying to occupy Hawaii. The US would probably decide to focus on the more immediately threatening foe, Britain, and thus concentrate their navy on the eastern coast. The English know they need to knock out the US very quickly, and decisively enough that they have enough freedom to destroy naval infrastructure through coastal bombardment (harder than it sounds) because otherwise the war effort is doomed. Assuming they
can pull this off, presumably by forcing the Americans to battle through indiscriminate bombardment of urban areas, they'd then not only have to win, but win strongly enough that they can then enact a blockade and grueling campaign to dismantle the east coast's naval infrastructure. It just seems like proposing scenarios where the Nazis could win WWII - somewhat fantastical if technically
possible propositions where a multitude of factors have to align and luck repeatedly work out in their favor.
Remember guys, this isn't WW2, this isn't FDR's well-oiled warmachine. This is 1915 America, where the standing army is frontiers men and the navy is a prestige project pushed by Teddy Roosevelt as a means s to project power.
I'd point out America has
always gone into these kinds of wars with a pathetic military, and repeatedly proven their ability to rapidly mobilize and modernize. Using terms like "FDR's well-oiled machine" and "Teddy's prestige project" are also just
blatantly incorrect. Considering the great depth of research and effort that has clearly gone into other nations in this quest, it's somewhat bizzaire that the United States is getting the half-assed pop-culture history treatment, to be perfectly honest.
But here's the thing, you can't interdict trade when your entire coastline blockaded, you haven't built new cruisers in almost ten years and your only modern ships are dreadnoughts. It doesn't work. The U.S. needs time to get going, and in 1915, it doesn't have that if it goes to war with Britain and Japan at the same time.
... But it does. The scenarios you are describing are absurd.
Every bit of this scenario is absurd, when you get down to it.
The U.S. wasn't exactly the only country gripped by the great depression - the reading Japan's economic history from 1920 to 1936 is basically one market crash after another, and the U.K. as mentioned, never recovered from WW1. America might necessarily "lose" said war in the sense that it could very well be status quo ante bellum, but it certainly won't win it either. Especially on the naval side of things.
While Japan's economy repeatedly crashed, stuff like annexing Manchuria did wonders to help industrialized, and the militaries supremacy did mean that a great deal was spent on furnishing, well, the military. I think it's a fair statement to make that Japan would benefit from two decades of time more than the US.
I continue to maintain the stance that what you're describing, both in the USA's conduct and the hypothetical war, are erroneous, and hope this makes you reconsider some of these opinions.
It is now 02:35 and I am going to sleep.
Good night.
It's important to remember that the USA was exceptional in its racism for the time period even when compared to other Western nations. Not saying that Britain and France were little angels, but they didn't have formal apartheid and the sort of monomaniacal devotion to white supremacy that is at the bedrock of American thought and belief in the time period (...and other time periods). Racism isn't an, "and also this!" in this time period, but "freedom, liberty, and the subjugation of the [censored], [censored], and [censored]".
Oh no, of course not. Why implement apartheid in your own lands when you can just do it in your
vast colonies.
So...yeah. I'm not sure how wise it is to be an envoy to a nation whose interests are diametrically opposed to ours and whose people see us as something between apes and aliens. I think the wiser course is to thwart American Pacific ambitions by allying with the British. Raise the costs of hostile action to the point where the Americans relent.
I'd hardly describe the current situation as the nations being 'diametrically opposed,' nor racist prejudice (of which the Japanese were hardly clean of) interfering in Realpolitik to a meaningful extent.