How real was the threat of invasion of the continental US - particularly the East Coast - in the 1942-43 time frame?

The English Channel was too much of an obstacle to invade Britain; Germany never had the surface naval power to mount a credible invasion of the USA. Which is not to say that it could not have been developed, but logistics argue strongly against it.

One of the primary reasons to invade the USSR in 1941 was to acquire the oil fields around the Black Sea. In fact, that might have been achieved had the political desire to take over Stalingrad and Moscow not been equally compelling to Hitler. Had Hitler taken the oil, then there’s no telling how the rest of the war might have played out.

There was an attack on the East Coast, and it was very successful. It was never followed up.

My dad served on board a US Navy destroyer in WWII. Those ships were designed to chase subs, and he used to tell us about the U-boats in the Atlantic. I remember him talking about the one they sank right off the coast. Up until recently, I could never confirm the incident, until someone did a FOIA request, and it was then that I discovered this wasn’t a fluke.

The oceans would not have been any obstacle I would have worried about had I been the one to consider invading The United States! It would have been ALL THOSE Americans and their GUNS! EVERYBODY and his/dog would have been shooting at the invaders!!! Pure suicide!

Even under pressure from millions of Allied troops on the continent, the German advanced weapons programs were making huge progress.

If they had taken Britain and there was no Allied invasion, the Germans might have developed missiles and/or bombers to hit the US.

Even then I don’t think there would have been a danger of invasion. But they could have forced an end to the war on terms very favorable to Germany.

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An invasion of the US in 1942–1943 by Nazi Germany was entirely out of the question. Even if Britain had surrendered right after France did, the Germans were not prepared to mount a trans-Atlantic invasion, and had no plans to do so.

I guess if you posit a miraculous timeline it might be possible in 1943, if it looked a bit like this:

1940: France and Britain surrender.
1941: Germany invades Russia earlier in the year than it did, weather cooperates much more than it did historically. Germany captures Moscow and Stalin, Russia surrenders.
1942: Germany builds up infrastructure and equipment, and takes over the entirety of the French and British navies. Japan does not start war with the USA, who do not start war mobilization.
1943: Japan and Germany both attack the USA. With no other fronts to worry about, and all the military and civilian ships from France, England, Germany and Italy, they actually have some way of conducting an invasion and supplying it.

That last detail is one of the main reasons why not. With only German ships, there was no way to conduct an invasion and keep it supplied. Even so, I’m not sure it would be logistically possible because of the enormous sea distance. The only way the USA was able to invade Nazi-occupied France was by stockpiling men and supplies at logistics bases in Britain for months before the invasion.